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Cummins/Onan NT855 Engine

Name: Cummins/Onan NT855 Engine
Brand: Cummins/Onan

The Cummins/Onan NT855 is a 8.55 L 6-cylinder turbocharged engine rated at 1800 rpm, producing up to 354 kW. It powers generator sets from Cummins/Onan, including the C350 D5, C350 D6, C400 D5 and C400 D6. It holds 40 L (10.6 gal) of oil and 51 L (13.5 gal) of coolant.

Also known as: Cummins NT855, NT 855

Part of the Cummins/Onan NT855 engine family — 6 variants share parts & fitment.

8.55 L

Displacement

Cylinders

1800 rpm

Rated speed

354 kW

Gross power

On this pageSpecs Generator sets Maintenance FAQ Service intervals Torque & specs Fluids Fault codes Procedures Wiring

Engine specifications

Oil capacity	40.0 L
Coolant capacity	51.0 L
Displacement	8.55 L
Cylinders	6
Aspiration	turbocharged
Rated speed	1800 rpm
Gross power	354 kW

Generator sets powered by this engine

Cummins/Onan C350 D5 Cummins/Onan C350 D6 Cummins/Onan C400 D5 Cummins/Onan C400 D6 Cummins/Onan C440 D5 Cummins/Onan DFBFCummins/Onan NT 855

How to read your Cummins/Onan engine serial & model number →

Common problems

UNDER FREQUENCY 313
Fix: Shutdown
SHORT CIRCUIT 322
Fix: Shutdown
Over Current 1471
No AC output voltage.
Fix: Contact an authorized service center.
LOW OIL PRESSURE 200
Fix: Shutdown
Low Coolant Level 197
LOW AC VOLTAGE 303
Fix: Shutdown
High Coolant Temp 211
Fix: Indicates engine has begun to overheat and coolant temperature has risen to an unacceptable level: (215° F − standby / 207° F − primary).
HIGH AC VOLTAGE 301
Fix: Shutdown
Weak Battery 1442
Warning, Shutdown, and Non-Automatic lamps are not lit. Digital display shows main menu or selected menu.
Cause: Indicates all engine systems are normal. No corrective action required
Warning lamp lights. MESSAGE: WEAK BATTERY 232 - WARNING 232
Fix: Indicates battery voltage drops below 60% of nominal for two seconds, during starting. a. Discharged or defective battery. See Warning message 230, LOW DC VOLTAGE.
Warning lamp lights. MESSAGE: RUPTURE BASIN 262
Warning lamp lights. MESSAGE: OVERLOAD 330
Fix: Indicates that three-phase power output exceeds 105% of standby (or 115% of prime) rating. After five seconds, the Load Dump output is activated. After 60 seconds, the OVERLOAD warning is activated. Contact an authorized service center.
Warning lamp lights. MESSAGE: OVERCURRENT 320
Fix: Indicates that generator output current has exceeded 110% of rated for 60 seconds. Contact an authorized service center.

Compiled from service & troubleshooting documentation across every generator set that uses the Cummins/Onan NT855.

Maintenance schedule

Item	Spec	Capacity	Part #	Interval
Air filter	air cleaner		—	1000 hr
Fuel filter	fuel filter		—	500 hr
Oil filter	engine oil filter		—	1000 hr
Battery	batteries		—	500 hr
Belt	fan belt, water pump belt		—	1000 hr
Coolant	cooling system	80.63 L	—	5000 hr
Coolant filter	Refer to Cummins engine Operation and Maintenance Manual.		—
Oil	engine oil	7.0 U.S. gallons	—	100 hr
Spark plug	spark plugs		—	1000 hr

Pooled from every document that names this exact engine — confirm the interval and part number against your unit's serial number.

Service intervals

Item	Action	Hours	Months	Notes
Genset	Inspect	8 hr		Inspect for oil, fuel, cooling and exhaust system leaks. Check exhaust system audibly and visually with set running (footnote X1).
Air Cleaner	Check	50 hr		Clean if required. Perform more often in dusty conditions (footnote X2).
Battery Charging System	Check	50 hr
Charge Air Piping	Check	50 hr
Coolant Heater	Check	50 hr		Column alignment in source table is ambiguous; interval as printed in schedule columns.
Coolant Level	Check	50 hr
Crankcase oil	Change	50 hr		First service — Break-in: drain and replace crankcase oil after first 50 hours on new generator sets
Fuel Level	Check	50 hr
Oil Level	Check	50 hr
Anti-freeze and DCA Concentration	Check	100 hr		Refer to engine operation and maintenance manual for procedure (footnote X5).
Drive Belt Tension	Check	100 hr		Visually check belt for evidence of wear or slippage; replace if hard or brittle (footnote X3). Refer to engine operation and maintenance manual (footnote X5).
Exhaust Condensate Trap	Drain	100 hr
Fuel Filter(s)	Drain	100 hr		Drain 1 cup or more of fuel to remove water and sediment (footnote X4); refer to engine operation and maintenance manual (footnote X5).
Water and Sediment from Fuel Tank	Drain	100 hr		Drain 1 cup or more of fuel to remove water and sediment (footnote X4).
Air Cleaner Element	Change	250 hr		Perform more often in dusty conditions (footnote X2).
Coolant Filter	Change	250 hr		Refer to engine operation and maintenance manual for procedure (footnote X5).
Crankcase Breather	Clean	250 hr		Refer to engine operation and maintenance manual for procedure (footnote X5).
Crankcase oil and filter	Change	250 hr	12 mo	Table 7-1. If genset used for prime power, change every 6 months or 250 hours. If standby, change every 12 months or 250 hours, whichever comes first.
Starting Batteries	Check	250 hr
Cooling System	Clean	500 hr		Refer to engine operation and maintenance manual for procedure (footnote X5).
Fuel Filters	Change	500 hr		Refer to engine operation and maintenance manual for procedure (footnote X5).
Radiator Hoses for Wear & Cracks	Check	500 hr	12 mo
Rupture basin leak detect switch	Test		12 mo	Some areas may require weekly inspections by safety code.

Extracted from the manufacturer documentation linked to this model. Values are copied as printed; confirm against your unit's manual and serial number.

Service specifications

Type	Item	Value	Unit	Condition
Clearance	Coolant level below radiator cap opening	about two inches (50 mm)	in (mm)	engine cold
Clearance	Float switch assembly float lift clearance below C-clip stop	1/8	inch (3 mm)	use a feeler gauge
Clearance	Generator-to-engine angular alignment (T.I.R.)	.001 in. per inch of radius (center of shaft to indicator axis), maximum	in	750 kW gensets and larger
Clearance	MPU sensor to gear tooth adjustment	back out one quarter turn	turn	after contacting gear tooth
Clearance	Vibration isolator base elevation difference	0.25	inch (6 mm)	all isolator bases within this elevation of each other
Clearance	Vibration isolator clearance between top plate and base	0.25	inch (6 mm)	nominal or greater
Clearance	Vibration isolator top plate to base clearance	0.25	inch (6 mm)	nominal, or greater
Gap	Air cleaner cleaning nozzle distance	1	inch (25 mm)	at least
Gap	Angular alignment total indicator reading (T.I.R.)	0.001	inch per inch of radius	maximum
Gap	Float switch lift to test open	1/8	inch	below C-clip stop
Other	AVR Droop setting	5	% at full load, 0 PF
Other	AVR voltage regulation (load regulation)	approximately ±0.5	% RMS
Other	Angular alignment maximum T.I.R.	.001	inch per inch of radius	center of shaft to indicator axis
Other	Battery electrolyte specific gravity, charge if below	1.215
Other	Battery electrolyte specific gravity, fully charged (corrected)	1.260		corrected; add 0.004 per 10°F above 80°F (27°C)
Other	Battery specific gravity	1.260	specific gravity	at 80 F (27 C)
Other	Battery specific gravity (high ambient, above 95F/35C)	1.225		recommended to reduce electrolyte loss
Other	Battery specific gravity (recharge threshold)	below 1.260
Other	Breather cleaning compressed air	30	psi	maximum (OSHA)
Other	Cool-down at idle timer range	0 to 30	minutes
Other	Cycle cranking option	15-second crank, 15-second rest, 3 cycles
Other	GOV GAIN default value for paralleling applications	70	%
Other	Over/Under Frequency Sensor Module - Over Hz Set, 50 Hz nominal	55	Hz	reset 53 Hz
Other	Over/Under Frequency Sensor Module - Over Hz Set, 60 Hz nominal	65	Hz	reset 63 Hz
Other	Over/Under Frequency Sensor Module - Under Hz Set, 50 Hz nominal	45	Hz	reset 47 Hz
Other	Over/Under Frequency Sensor Module - Under Hz Set, 60 Hz nominal	55	Hz	reset 57 Hz
Other	Over/Under Voltage Sensor Module time delay	typically 25 percent, approximately 2.5	seconds
Other	Overcrank cranking limit	75	seconds	three 15-second cranking cycles with two 15-second rest periods
Other	Overcrank cranking limit (standard control)	75	seconds
Other	REG VHZ (underfrequency roll-off) adjustable range	1 through 50; normal range 7 through 21
Other	Rated To Idle delay range	0 to 10	seconds	default = 0; Beginning Version 2.303
Other	Start Delay setting range	0 to 300	seconds	default = 0
Other	Start delay adjustment range	0 to 300	seconds
Other	Stop Delay setting range	0 to 600	seconds	default = 0
Other	Stop delay adjustment range	0 to 600	seconds
Other	Under Frequency Roll Off (UFRO) knee point, 50 Hz units	48 to 49	Hz
Other	Under Frequency Roll Off (UFRO) knee point, 60 Hz units	58 to 59	Hz
Other	Warm-up at idle time delay range	0-300	seconds
Pressure	Air cleaner cleaning compressed air	30	psi (207 kPa)	maximum
Pressure	Engine oil pressure - K19 normal	50-70	psi (345-482 kPa)	run mode
Pressure	Engine oil pressure - K38 normal	45-65	psi (310-448 kPa)	run mode
Pressure	Engine oil pressure - K50 normal	50-70	psi (345-482 kPa)	run mode
Pressure	Engine oil pressure - L10/M11 normal	30-50	psi (207-345 kPa)	run mode
Pressure	Engine oil pressure - NTA 855 normal	35-50	psi (241-345 kPa)	run mode
Pressure	Engine oil pressure - V28 normal	50-90	psi (345-620 kPa)	run mode
Pressure	Engine oil pressure shutdown limit - L10/M11	20	psi (138 kPa)	run mode value
Pressure	Engine oil pressure shutdown limit - L10/M11	8	psi (55 kPa)	idle mode value
Pressure	Engine oil pressure warning limit - L10/M11	12	psi (83 kPa)	idle mode value
Pressure	Engine oil pressure warning limit - L10/M11	25	psi (172 kPa)	run mode value
Pressure	Idle oil pressure shutdown limit	12	psi (83 kPa)
Pressure	Idle oil pressure shutdown limit (PCC)	12	psi (83 kPa)	idle
Pressure	Idle oil pressure warning limit	15	psi (104 kPa)
Pressure	Idle oil pressure warning limit (PCC)	15	psi (104 kPa)	idle
Pressure	K19 engine idle oil pressure	20	psi (138 kPa)	idle
Pressure	K19 engine normal oil pressure	50-70	psi (345-482 kPa)	normal run
Pressure	K19 oil pressure shutdown/warning limits	shutdown 35 psi (241 kPa) run; warning 40 psi (276 kPa) run; shutdown 10 psi (69 kPa) idle; warning 15 psi (103 kPa) idle	psi (kPa)
Pressure	K38 engine idle oil pressure	20	psi (138 kPa)	idle
Pressure	K38 engine normal oil pressure	45-65	psi (310-448 kPa)	normal run
Pressure	K38 oil pressure shutdown/warning limits	shutdown 35 psi (241 kPa) run; warning 40 psi (276 kPa) run; shutdown 10 psi (69 kPa) idle; warning 15 psi (103 kPa) idle	psi (kPa)
Pressure	K50 engine idle oil pressure	20	psi (138 kPa)	idle

Extracted from the manufacturer documentation linked to this model. Values are copied as printed; confirm against your unit's manual and serial number.

Recommended fluids

Fluid	Grade	Standard	Ambient	Capacity	Notes
Coolant	Water/antifreeze mixture precharged with Diesel Coolant Additive (DCA)	Engine manufacturer's coolant requirements; do not use antifreeze with anti-leak additives		62.0 L	Standard radiator capacity 16.5 gallons (62 L) for 275 DFBF
Coolant	soft water / E.G. / DCA mixture				Cooling system to be filled with soft water/E.G./DCA mixture (on-site review checklist).
Coolant		NFPA 110	above 4°C		NFPA 110 recommends engine jacket water coolant heaters where minimum ambient is above 40°F (4°C); coolant maintained at minimum 90°F (32°C). Cooling system capacity with standard radiator: DFAB/DFAC 13 Gal (49 L); DFBF 13.5 Gal (51 L); DFCC 13.5 Gal (51 L); DFCE 15 Gal (57 L).
Engine oil		API Class CC/CD		42.0 quarts	Oil capacity with filters (all models)
Engine oil	SAE 5W synthetic	API Class CC/CD; pour point 9 F (5 C) below lowest expected temperature; viscosity 10,000 mPa-s max at -31 F (-35 C) and 4.1 mm2/s min at 212 F (100 C)	below -25°C		Extreme cold: consistently below -13 F (-25 C) with no provision to keep engine warm
Engine oil	SAE 10W-30	API Class CC/CD, max 1.85% sulphated ash	-23°C to -10°C		Table 5-2; Specification section lists 10W-30 for -13 F to 95 F (-25 C to 35 C)
Engine oil	SAE 15W-40	API Class CC/CD, max 1.85% sulphated ash	above -10°C		Table 5-2: 14 F (-10 C) and above; Specification section: -14 F (-10 C) and above
Engine oil	SAE 20W-40	API Class CC/CD, max 1.85% sulphated ash	above 0°C		32 F (0 C) and above
Fuel		Diesel fuel			Do not use zinc coated or copper fuel lines with diesel fuel. Fuel connection at the engine should be made with an approved flexible line.
Fuel	ASTM No. 2 diesel	Cummins engine Operation and Maintenance Manual alternate diesel fuels			Cummins engines normally use ASTM No. 2 diesel fuel. Never use galvanized or copper fuel lines, fittings or fuel tanks.
Fuel	ASTM No. 2 diesel fuel	ASTM No. 2			Cummins engines normally use ASTM No. 2 diesel fuel; they will operate on alternate diesel fuels within the specifications shown in the Cummins engine Operation and Maintenance Manual. Never use galvanized or copper fuel lines, fittings or fuel tanks.
Fuel	Diesel				Day tank fuel transfer pump maintains reservoir of diesel fuel in the day tank.
Fuel	No. 2 Diesel Fuel; Bio-Diesel B5-B20 approved with recommendations	ASTM D975 (post-storage purge fuel)			Bio-diesel not recommended for Emergency Standby RV use (low annual hours, critical start nature).
Fuel	No. 2 diesel (No. 1 acceptable)				Filter or strain fuel as tank is filled; keep tanks full to avoid condensation
Grease	Lithium based		-30°C to 120°C	81.0 ml	Mobilux No. 2 or Shell Alvania R3; generator end bearing; temperature range -22 F to +248 F (-30 C to +120 C); grease divided between bearing, bearing cap cavity and cartridge cavity.
Grease	Lithium based grease, Mobilux No. 2 or Shell Alvania R3		-30°C to 120°C	2.74 oz (81 ml)	End bearing lubricant; grease equally divided between bearing, bearing cap cavity and bearing cartridge cavity.

Extracted from the manufacturer documentation linked to this model. Values are copied as printed; confirm against your unit's manual and serial number.

Fault codes

Code	Name	Meaning	Severity	Action
101	IDLE MODE	Indicates that the engine is operating in idle mode. Grounding the engine idle input causes generator build-up to be inhibited and the engine to be governed at 800 RPM.	Warning	Remove ground from engine idle input to return to normal speed and voltage.
102	EMERGENCY STOP	Local or remote Emergency Stop.	Shutdown	Turn the switch clockwise and allow it to pop out (local only). Move the Run/Off/Auto switch to Off. Press the Reset switch. Select Run or Auto, as required.
1122	Rated/Idle Trans
1123	Shutdown After BS	Shutdown fault occurred while Battle Short was enabled and then disabled.	Shutdown	Review Fault History and perform corrective action.
1124	Delayed Shutdown	Shutdown fault became active while Delayed Shutdown feature was enabled.	Warning	Review Fault History and perform corrective action.
1131	Battle Sh Active	Control is in Battle Short mode.	Warning	Bypasses several critical fault shutdowns for emergency operation.
121	Speed Signal Lost	Mag pickup speed indication is not being sensed.	Shutdown	Restart and check RPM on the digital display.
1311	Customer Input #1	The nature of the fault is an optional customer selection. Example inputs: Low Fuel Day Tank, Water In Fuel, Ground Fault, Low Starting Hydraulic Pressure, Low Starting Air Pressure, etc.		Enable/disable input (Default: enable); Status, Warning or Shutdown (Default: #1-None, #2 thru #4-Warning); Active closed or open (Default: closed [ground]); change display name up to 19 characters (Default: #1-Customer Fault 1).
1311, 1312, 1317, 1318	CUSTOMER INPUT #1 - #4	Optional customer-selected fault input is active.	Warning	Check external wiring and active input (closed/open) selection.
1312	Customer Input #2	Default display name: Ground Fault.		Configurable input; defaults #2 thru #4 = Warning.
1317	Customer Input #3	Default display name: Low Fuel.		Configurable input; defaults #2 thru #4 = Warning.
1318	Customer Input #4	Default display name: Rupture Basin Fault.		Configurable input; defaults #2 thru #4 = Warning.
1334	Crit Scaler OR	Incorrect feature or calibration entered into control.	Shutdown	Reload correct calibration.
1335	Noncrit Scaler OR	Incorrect feature or calibration entered into control.	Warning	Reload correct calibration.
1337	No Message
135	Oil Pressure Sensor H	Engine oil pressure sender signal is shorted high.	Warning	Check sender/connectors/wires.
141	Oil Pressure Sensor L	Engine oil pressure sender signal is shorted low.	Warning	Check sender/connectors/wires.
1416	Fail To Shutdown	Genset continues to run after shutdown command.	Warning	Check Battle Short feature enabled condition.
1417	Powr Down Error	Indicates that the controller can not power down because of some unknown condition. Possible drain on battery.	Warning	Contact an authorized service center for service.
143	Pre-Low Oil Pres	Indicates engine oil pressure has dropped to an unacceptable level. If generator is powering critical loads and cannot be shut down, wait until next shutdown period and then follow code 415 procedure.	Warning	If powering critical loads and cannot be shut down, wait until next shutdown period and follow code 415 procedure.
1433	Emergency Stop	Local Emergency Stop.	Shutdown	To reset: pull the button out; move the O/Manual/Auto switch to O; press the front panel Fault Acknowledge/Reset button; select Manual or Auto as required.
1434	Remote E-Stop	Remote Emergency Stop.	Shutdown	See code 1433 to reset.
1435	Low Coolant Temp	Warning occurs when engine coolant temperature is 70°F (21°C) or lower. In applications where the ambient temperature falls below 40°F (4°C), Low Coolant Temp may be indicated even though the coolant heaters are operating.	Warning	Indicates engine coolant heater is not operating or is not circulating coolant. Check that coolant heater is connected to power supply (check for blown fuse or disconnected heater cord). Check for low coolant level and replenish if required; look for possible coolant leakage points and repair as required.
1438	Fail To Crank	Indicates possible fault with control, speed sensing or starting system.	Shutdown	See code 441 for corrective action.
144	Coolant Sensor High	Engine coolant temperature signal is shorted high.	Warning	Check sender/connectors/wires.
1442	Weak Battery	Indicates that during cranking, the battery voltage is at or below the weak battery warning trip point for a time greater than or equal to the weak battery set time.	Warning	See code 441 for corrective action.
1443	Battery Failed	Dead battery - engine will not start.	Shutdown	See code 441 for corrective action.
1444	KW Overload	Generator output power exceeded 105% of genset rating.	Warning	Check load and load lead connections; check CTs.
1445	Short Circuit	Generator output current has exceeded 175% of rated.	Shutdown	Check load and load lead connections.
1446	High AC Voltage	One or more phase voltages exceeded 130% of nominal.	Shutdown	Check fault simulation, load removal, threshold settings, Base board/generator.
1447	Low AC Voltage	Phase voltages dropped below 85% of nominal for 10 seconds.	Shutdown	Check overload, output terminal connections, PMG/field wiring, rectifier diodes.
1448	Under Frequency	Engine speed dropped below 90% of nominal for 10 seconds.	Shutdown	Check fuel supply, intake air supply and load.
1449	Over Frequency	Frequency is 10% above base frequency for 20 seconds.	Warning	Check fuel or air delivery; check connections.
145	Coolant Sensor Low	Engine coolant temperature signal is shorted low.	Warning	Check sender/connectors/wires.
1452	Gen CB Not Close	Genset circuit breaker (S2) failed to close when PTC is enabled.	Warning	Refer to Section 5 troubleshooting charts.
1453	Gen CB Not Open	Genset circuit breaker (S2) failed to open when PTC is enabled.	Warning	Refer to Section 5 troubleshooting charts.
1459	Reverse Power	Improper CT phasing.	Shutdown	Check wiring to voltage sense circuit; refer to CT Installation in Section 6.
146	Pre-High Coolant Temp	Indicates engine has begun to overheat (coolant temperature has risen to an unacceptable level).	Warning	Reduce load; check air inlets/outlets; follow code 151 if engine can be stopped.
1461	Loss Of Field	Loss of field (electric) due to reverse kVAR.	Shutdown	Check excitation circuit.
1466	Modem Failure	Control cannot communicate with the modem.	Warning	Check for open, short to ground and loose connections to the modem.
1468	Network Error	Momentary loss of communication from the LonWorks Network.	Warning	Refer to LonWorks Network publications.
1469	Speed/Hz Match	Measured speed and measured AC output frequency do not agree.	Shutdown	Check calibration file.
1471	Over Current	Generator output current exceeded 110% of rated for 60 seconds.	Warning	Check load and load lead connections.
1472	Over Current	Output current exceeded 110% of rated and time/current calculation initiated shutdown.	Shutdown	Check load and load lead connections.
151	High Coolant Temp	Indicates engine has overheated (coolant temperature has risen above the shutdown trip point). Allow engine to cool down completely before proceeding.	Shutdown	Check coolant level and replenish if low; look for coolant leakage points and repair. Check for obstructions to cooling airflow. Check fan belt and repair or tighten if necessary. Check blower fan and circulation pumps on remote radiator installations. Reset control and restart after correcting problem.
197	Low Coolant Level	Indicates engine coolant level has fallen below the warning trip point (optional).	Warning	If powering critical loads and cannot be shut down, wait until next shutdown period, then follow code 235 procedure. If engine can be stopped, follow code 235 procedure.
200	LOW OIL PRESSURE	Indicates engine oil pressure has dropped to an unacceptable level.	Warning	If powering critical loads, wait until next shutdown period then follow 201 procedure.
201	LOW OIL PRESSURE	Indicates engine oil pressure has dropped below the shutdown trip point.	Shutdown	Check oil level, lines and filters; replenish if low; reset control and restart; contact service center.
204	OIL PRES SENDER	Indicates that the control has sensed that the engine oil pressure sender is out of its working range.	Warning	Check that the engine oil pressure sender is properly connected. Contact service center.
210	LOW COOLANT TEMP	Warning occurs when engine coolant temperature is 70°F (21°C) or lower.	Warning	Warning LED illuminates. Check the coolant heaters for proper operation; if operating properly, other precautions may be necessary to warm the engine before applying a load.
211	HIGH COOLANT TEMP	Indicates the engine coolant temperature is getting close to the recommended maximum temperature limit: 215° F (102° C) − standby or 207° F (97° C) − primary.	Warning	Reduce load; check air inlets/outlets and remove obstructions.
212	Oil Temp Sensor H	Indicates engine has overheated (coolant temperature above 215° F (102° C) − standby or 207° F (97° C) − primary).	Warning	Check sender/connectors/wires.
213	Oil Temp Sensor L	Resistance of the coolant temperature sender is out of range.	Warning	Contact an authorized service center.
214	LOW COOLANT LVL	Indicates engine coolant level has fallen below the trip point.	Warning	Check coolant level in radiator and coolant recovery bottle; replenish if low; look for leaks.
215	LOW COOLANT LVL	Indicates engine coolant level has fallen below the trip point.	Shutdown	Allow engine to cool; check coolant level and replenish; look for leaks and repair; reset and restart. Shutdown will not occur in Idle mode.
220	MAG PICKUP	Mag pickup speed indication not sensed or does not match generator set output frequency.	Shutdown	Restart and check RPM; check PCC model setting; inspect and test MPU.
221	FAIL TO CRANK	Possible fault with control or starting system.	Shutdown	Check fuse F3 on the Engine Interface board. Check for poor battery cable connections; clean battery cable terminals and tighten. Recharge or replace a discharged or defective battery.
222	OVERCRANK	Possible fuel system problem.	Shutdown	Check for empty fuel tank, leaks, plugged fuel lines; replace dirty fuel or air filter; reset and restart.
223	OVERSPEED	Indicates engine has exceeded normal operating speed. (115% ±1% of nominal).	Shutdown	Contact an authorized service center.
224	FAIL TO SYNCHRONIZE	Generator set has not synchronized to the system bus within the allowable time frame.	Warning	Check governor system stability; adjust governing and synchronizer parameters; check fuel system.
226	FAIL TO CLOSE	Paralleling breaker has been given a signal to close, but has not closed properly.	Shutdown	Verify breaker charging mechanism; check close signal; verify auxiliary contact signals.
230	LOW DC VOLTAGE	Indicates battery voltage is below 10 VDC.	Warning	Recharge or replace the battery; check the battery charger fuse. Clean and tighten battery cable connections. Check engine DC alternator; replace if normal charging voltage is not obtained. Check float level if applicable.
231	HIGH DC VOLTAGE	Indicates battery voltage exceeds 32 VDC.	Warning	Lower battery charger float level if applicable; check engine DC alternator.
232	WEAK BATTERY	Indicates battery voltage drops below 60% of nominal for two seconds, during starting.	Warning	See Warning message 230, LOW DC VOLTAGE.
2327	PTC Fault	PTC module or communication link is not working properly.	Warning	Check PTC module power, ground shield, cycle control power.
2329	Low S1 Frequency	Low utility (S1) frequency.	Warning	Check S1 AC inputs and wiring to PTC at TB5; check sensor set points.
2331	Low S1 Voltage	Low utility (S1) voltage.	Warning	Check S1 AC inputs and wiring to PTC at TB5; check pickup/dropout set points.
2335	Excitation Fault	Loss of all three voltage sense leads or failure in excitation circuit.	Shutdown	Check field wiring (X1 and X2) for shorts or opens.
2336	Memory Error	Control memory error; data corruption of critical operating parameters.	Shutdown	Try reloading calibration file.
2337	Pwr Tran Disabled	PTC module available but PTC feature not enabled.	Warning	Enable PTC feature with InPower; cycle control power.
2338	Pwr Tran Failure	Control could not communicate with the PTC module.	Warning	Check PTC module power and cable ground shield; cycle control power.
2339	Pwr Down Enabled	Power Down (sleep) enabled but PTC module or network board is active.	Warning	None required.
234	Overspeed	Engine has exceeded normal operating speed.	Shutdown	Check for large block load removal, flammable vapors or leaking turbocharger seals.
2341	High Control Temp	Control temperature above 158 F (70 C) for longer than set time.	Warning	Check genset room air flow.
2342	Too Long In Idle (10 min.)	Indicates genset has been in Idle mode too long (10 minutes maximum).	Warning	Exit idle mode.
235	Low Coolant Level	Indicates engine coolant level has fallen below the shutdown trip point (optional). Allow engine to cool down completely before proceeding.	Shutdown	Check coolant level and replenish if low; reset control.
2358	High S1 Voltage	Utility (S1) voltage increased above the over-voltage threshold.	Warning	Measure S1 AC inputs at PTC module; check sensor set points.
2396	S1 CB Not Close	Utility contact (S1) failed to close with PTC enabled.	Warning	Refer to Section 5 troubleshooting charts.
2397	S1 CB Not Open	Utility contact (S1) failed to open with PTC enabled.	Warning	Refer to Section 5 troubleshooting charts.
240	LOW FUEL−DAY	Indicates day tank fuel supply is running low.	Warning	Check fuel supply and replenish as required.

Extracted from the manufacturer documentation linked to this model. Values are copied as printed; confirm against your unit's manual and serial number.

Procedures

Adjust Start/Stop Delays (PCC Adjust Menu) adjustment

⚠ Electrostatic discharge will damage circuit boards. Always wear a grounding wrist strap when working inside control box.

Press the button next to ADJUST in the Main Menu; the VOLTAGE submenu appears.
Press the button next to >> to move through VOLTAGE and FREQUENCY to the START DELAY submenu.
Use the buttons next to the up and down symbols to set the start delay.
Press >> to move to the STOP DELAY submenu and set the stop delay.
Press >> to move to the IDLE SPEED submenu and set idle speed (only in idle mode).
Press >> to move to SAVE/EXIT; select SAVE then EXIT to return to Main menu.

Adjusting Values/Parameters (PCC Adjust Menu) adjustment

Press the button next to the arrow symbol in the display until the + and - symbols are displayed.
If necessary, press the button next to the arrows to move to the numeric character to change.
Press + to increase the value or select the parameter; press - to decrease the value or select the parameter.
Press the save symbol to save changes; changes are not saved if Home or Previous Main Menu is pressed first.

Aligning Generator with Engine (Angular Alignment) adjustment

⚠ Accidental starting of the generator set during this procedure presents the hazard of severe personal injury or death.

Tools: Dial indicator, Shims

Disconnect the negative (-) battery cable(s) before beginning.
Fasten a dial indicator to the generator shaft or cooling fan with the sensing point on the capscrew head or flat surface of the drive disc at the bolt circle diameter.
Bar the engine over in a clockwise rotation as viewed from engine flywheel; do not allow it to roll back on compression.
Determine the total indicator reading (T.I.R.) as the sum of the maximum positive and negative dial indicator readings over one revolution.
Measure the distance from the center of the generator shaft to the indicator measuring point.
Measure the distance from the generator side of the flex discs to the center of the generator mounting bolt.
Compare the distances; multiply this ratio times one half the T.I.R. to approximate the amount of shims to remove or add.

Angular Alignment Procedure (750 kW Gensets and Larger) adjustment

⚠ Accidental starting of the generator set during this procedure presents the hazard of severe personal injury or death. Make sure to disconnect the negative (-) battery cable(s) before beginning.

⚠ Do not bar engine over by prying on fan blade.

Tools: Dial indicator, Shims

Disconnect the negative (-) battery cable(s) before beginning.
Fasten a dial indicator to the generator shaft or cooling fan, with the sensing point on the capscrew head or drive disc flat surface at bolt circle diameter.
Bar the engine over clockwise as viewed from the engine flywheel; do not allow it to roll back on compression.
Total indicator reading (T.I.R.) is the sum of the maximum positive and negative readings as the engine completes one revolution.
To lower the generator, remove equal shims from under both generator mounting feet; approximate shim amount from the distance ratio.

Angular Alignment Procedure (Generator to Engine) adjustment

⚠ Accidental starting during this procedure presents the hazard of severe personal injury or death.

⚠ Do not bar engine over by prying on fan blade.

Tools: dial indicator

Disconnect the negative (-) battery cable(s) before beginning.
Fasten a dial indicator to the generator shaft or cooling fan with sensing point resting on the drive disc capscrew head/flat surface at the bolt circle diameter.
Bar the engine over in a clockwise rotation as viewed from the engine flywheel; do not allow it to roll back on compression at the end of travel of each reading.
Record the total indicator reading (T.I.R.) as the sum of the maximum positive and negative dial indicator readings over one engine revolution.
Compare the measured T.I.R. to the maximum allowed (.001 in. per inch of radius from center of shaft to indicator axis); add or remove shims under the generator mounting feet to correct.

Axial Alignment Procedure adjustment

Tools: Dial indicator, Magnetic base or clamp

Check axial alignment only when an objectionable vibration is present after angular alignment.
Fasten dial indicator holding device to skid base, engine block, or generator shell with a magnetic base or clamp; rest sensor on generator shaft hub.
Bar the engine over clockwise through a couple of rotations; record indicator readings at eight equally spaced points around the shaft diameter.
To correct out-of-tolerance T.I.R., remove the drive disc capscrews, mark discs and flywheel, rotate 180 degrees from original location, retorque, and recheck.
If unchanged, rotate the discs to 30, 60 or 90 degrees from their original location.

Axial Alignment Procedure (Generator to Engine) adjustment

Tools: dial indicator

Fasten a dial indicator holding device to the skid base, engine block, or generator shell with the sensor point resting on the generator shaft hub.
Bar the engine over in a clockwise rotation through a couple of rotations, recording indicator readings at eight equally spaced points around the shaft diameter to obtain axial T.I.R.
Reduce the measured T.I.R. runout by one half if excessive vibration remains after angular alignment.

Electric Governor Preliminary Adjustment adjustment

Turn idle speed potentiometer clockwise 20 turns, then 10 more turns.
Turn run speed potentiometer clockwise 20 turns, then 10 more turns.
Turn gain potentiometer fully counterclockwise.
Turn droop potentiometer fully counterclockwise for isochronous operation.

Governor Gain Adjustment adjustment

Close the main line circuit breaker and apply approximately 1/4 rated load.
Verify engine speed is constant.
Turn GAIN potentiometer clockwise slowly until engine speed is not constant.
Turn potentiometer counterclockwise until constant speed is achieved.
Turn counterclockwise an additional 1/2 division.

Voltage Adjustment adjustment

⚠ Do not adjust the factory-sealed V/HZ break point pot.

⚠ Hazardous voltage inside output box.

Remove the protective cover for access to the voltage adjusting pot and 50/60 Hz selector switch.
Check the position of the 50/60 Hz selector switch and change if necessary.
Adjust no-load voltage as required.
Replace the cover.

Cooling System Test (LAT calculation) diagnostic

Tools: Load bank, Thermocouples (No. 24 AWG or lighter)

Complete a representative installation.
Load the genset to rated full-load using a load bank.
Conduct the test at ambient >= 21 C (70 F).
Measure engine coolant outlet temperature and shielded ambient air temperature with thermocouples.
Expel air from the coolant system before testing; add coolant as necessary.
Run at full-load and record temperatures at 15-minute intervals until stable.
Calculate LAT = T(max) 107C - T(test) + T(amb); goal LAT >= 40 C (104 F).

Generator/Base Board Isolation Procedure diagnostic

⚠ This test involves unregulated excitation of the generator.

⚠ Hazardous voltage; use insulated tools and stand on dry platform.

Tools: Voltmeter, Jumper leads, 12V battery

Throw line circuit breaker OFF and shut down the set.
Disconnect exciter stator leads X and XX from AC harness.
Prepare to measure output voltage across generator terminals.
Bring 12V battery jumpers to X (Field +) and XX (Field -).
Verify polarity is correct before connecting.
Start set; connect battery negative to XX lead.
If rated voltage and balanced phases, generator is OK.
If unbalanced troubleshoot main stator; if low troubleshoot exciter circuits.

Extracted from the manufacturer documentation linked to this model. Values are copied as printed; confirm against your unit's manual and serial number.

Voltage reconnection

Voltage	Phase	Connection	Leads	Notes
		12 lead generator sets	Load wires are routed through the CTs	Reconnectable gensets (12 leads) have dual secondary CTs (3 pins); CT wire 2/3 to pin 2 (high voltage) or pin 3 (low voltage).
		6 lead generator sets	Generator output leads are routed through the CTs	Non-reconnectable gensets (6 leads) have single secondary CTs (2 pins).
		Cummins PowerCommand generic AC Reconnect Wiring Diagram 625-2755 (Rev. D) and 625-3100 (Rev. F)		Applies to models DFAA, DFAB, DFAC, DFBF, DFCB, DFCC, DFEB, DFEC, DFFB, DFGA, DFGB, DFJA, DFJB, DFJC, DFJD, DFLB, DFLC, DFLD, DFMB (625-2755) and models DFAA-DFMB plus DFCE, DFED, DQAA, DQAB, DQBA, DQBB (625-3100).
		Current transformers CT21-U load leads (A phase), CT22-V load leads (B phase), CT23-W load leads (C phase)	CT secondary wire marked 1 to pin 1; wire marked 2/3 to pin 2 for high voltage gensets or pin 3 for low voltage gensets	CT dot must face toward the generator; CTs have dual secondaries (3 pins).
		Generator load terminals stamped U, V, W and N (U=L1, V=L2, W=L3, N=L0)	Stranded load wires bolted to generator reconnection terminal block or circuit breaker lugs	Available generator output voltages and maximum current ratings are specified on the generator set nameplate; line-to-neutral is the lower voltage, line-to-line the higher. Reconnection diagram is located on the upper side cover of the control housing.
	A (U)	CT21	U load leads (A phase)	CT dot must face the generator; CT terminal 1 connects to metering circuit, terminal 2/3 to ground.
	B (V)	CT22	V load leads (B phase)	CT dot must face the generator; terminal 1 to metering circuit, terminal 2/3 to ground.
	C (W)	CT23	W load leads (C phase)	CT dot must face the generator; terminal 1 to metering circuit, terminal 2/3 to ground.
110 V - 120 V L-N	1	Single phase, 2-wire		PTC module jumper locations
190 V - 240 V L-L	3	Three phase		Use PTC module 0300-5382-01; 50/60 Hz
200 V - 240 V L-L	1	Single phase, 3-wire		PTC module jumper locations
380 V - 600 V L-L	3	Three phase		Use PTC module 0300-5382-02; 50/60 Hz

Extracted from the manufacturer documentation linked to this model. Values are copied as printed; confirm against your unit's manual and serial number.

Parts cataloged across the Cummins/Onan NT855 family

133

Part #	Description	Category
140-2389	Cleaner, Air (Includes Element)	air_filter
140-2391	Element - Air Cleaner (Standard)	air_filter
CS-1382c	INLET AIR DAMPER	air_filter
ES-1214-2	FLOAT SWITCH	air_filter
191-1982	Pulley, Alternator	alternator
191-1983-02	Alternator, 24 Volt Spec B-O (Prestolite)	alternator
A956	2-12 VOLT BATTERIES	battery
2110153	Bell, End - Alt, to Exciter	bell
511-0092	Belt, Alternator	belt
805-35	Bolt, Place - Gen. Mtg. support to End Bell	bolt
1S0A713	Bracket, Overspeed Switch	bracket
2348115	Bracket, Mtg. - Volt. Cont. Reactor	bracket
234875	Bracket, Gate Reactor Mtg.	bracket
301A1914	Bracket, Panel Stop	bracket
319-2236	Bracket, Mounting	bracket
234070	Rig Assy., Brush- Incl. Brushes, & Contact Point Band, Gen. - Front Portion(Narrow)	brush
2I4AM	Brush	brush
505-0019	Bushing, Pipe - Reducer 1/2” to 3/8”, DFBF (1/2” to 3/8”) 505-0131 DFCB, DFCC, DFCE (3/4” to 3/8”)	bushing
518-0548-58	Clamp, Hose	clamp
2340116	Cover, Exciter	cover
0300-4623-08	DFBF (600V)	current_transformer
0300-4623-23	DFBF BR (0-480V)	current_transformer
FS1803s	FUEL FILTERS	fuel_filter
FP-KS12622A	NH/NT855 In-Frame Kit w/upper gasket set & oil pan gasket	gasket
FP-KS12622C	NH/NT855 In-Frame Kit w/upper gasket set & oil pan gasket	gasket
FP-KS12622C7	NH/NT855 In-Frame Kit w/upper gasket set & oil pan gasket	gasket
FP-KS12622D	NH/NT855 In-Frame Kit w/upper gasket set & oil pan gasket	gasket
M-4024945	Edge molded rubber head gaskets set	gasket
232A1817	Generator	generator
502-0827	Hose, Barb (1/2–14)	hose
503-0189	Clamp, Hose	hose
503-1634-01	Hose, Rubber (3/4” ID x 4”)	hose
302P465	RESISTOR-STABILIZING	meter
302P466	For 220/380-V, 3-Ph, 60-Cycle (Model H)	meter
302P468	For 120/208-V,120/240-V, & 347/600-V 3PH. 50 Cy!. (825-Ohm, 75-Watt)	meter
302P469	For 220/380-V, 3Ph. 50-Cycle	meter
302P470	For 277/480-V, 3-Ph, 50-Cyclo (5-P!)	meter
309-0641-03	Switch, Low Oil Pressure (S110)	oil_filter
102-1335	Plug, Oil Drain	other_service
102206606	Safety Messages	other_service
130-3588	Cap, Radiator	other_service
130-4355	Radiator (2 Row Core) DFBJ	other_service
130-4355-01	Radiator (3 Row Core) DFCF, DFCG	other_service
130-4369	Radiator DFCH	other_service
155-2409-01	Elbow, Exhaust (5" OD With Threads)	other_service
191-1981	Genset component (SJB series)	other_service
191-2121	Regulator, Voltage	other_service
232A1489	Generator support shim, 0.598 in gauge #6, 3x3	other_service
232A1490	Generator support shim, 0.359 in gauge #20, 3x3	other_service
301021151	Box Only, control	other_service
30118301	Bracket, Cont.Box Mtg. (Repl. 2-Piece Brkts)	other_service
301A2727	Handle , Control Box	other_service
302-213	60-Cycle	other_service
302-234	.Cycle	other_service
3028448	Plate, Mater Face	other_service
302P411	~~ Scale Reads 0-200 (1-Phase Use 2)	other_service
302P412	Scale Reads 0-250	other_service
302P414	Amm, Scale Reads 0-300 - Replaces 302-14.	other_service
302P415	Ammeter Scale Reads 0-500 - Replaces 302-371.	other_service
302P422	Scale Reads 0-600	other_service
302P423	Scale Reads 0-750 on side of Gen	other_service
302P467	For 277/480 Volt,3 Phase, 60 Cycle Plants.	other_service
303-111	Rheostat, Volt. Reg. - 175-Ohm, (Model H)	other_service
303-32	Knob, Rheos	other_service
3040305	45, 000-Ohm, 10-W - For 480-V , 3-Ph, 3-Wire & 277/480-V, 3+ Ph.	other_service
308-22	Switch, Volt. & Current Selector Ammeter	other_service
32082	3-Phase Models	other_service
320B18	Single Phase Models	other_service
333-0639-01	Heater, Coolant (4990 Watt)	other_service
333-0639-02	Heater, Coolant (6420 Watt)	other_service
337A44	Strap, Grd. - Unhoused Plants	other_service
402-78	Rubber, Mtg. - Cont. Box	other_service
503-1575	Clamp, V-Band	other_service
504-0011	Valve, Shutoff (1/2”)	other_service
505-0100	Nipple, Pipe - Close (1/2”)	other_service
526-0219	Washer, Flat (1/2)	other_service
800-0048	Screw, Cap - Hex Head (3/8-16 x 3/4”)	other_service
850-0050	Washer, Lock - Spring (3/8”)	other_service
870-0212	Nut, Locking (1/4-20)	other_service
960-0138		other_service
960-0606		other_service
EXS-1046s	CONDENSATION TRAP	other_service
FP-855PREM	NH/NT855 Premium Cylinder Kits	other_service
FP-855TT	NT855 Premium 3-Ring Cylinder Kits	other_service
FP-855TTDN	NT855 Premium 3-Ring Cylinder Kits Dual-NI Pistons	other_service
FP-855TTP	NT855 Premium Plus 3-Ring Cylinder Kits	other_service
FP-855TTPDN	NT855 Premium Plus 3-Ring Cylinder Kits Dual-NI Pistons	other_service
FP-IFK855NR	NT855 Cylinder Kits w/ no piston rings	other_service
FP-IFK855PREM	NH/NT855 Premium Cylinder Kits	other_service
FP-IFK855TT	NT855 Premium 3-Ring Cylinder Kits	other_service
FP-IFK855TTDN	NT855 Premium 3-Ring Cylinder Kits Dual-NI Pistons	other_service
FP-IFK855TTP	NT855 Premium Plus 3-Ring Cylinder Kits	other_service
FP-IFK855TTPDN	NT855 Premium Plus 3-Ring Cylinder Kits Dual-NI Pistons	other_service
FP-KS12621C	NH/NT855 Cylinder Kit Std Head Gask Grommets	other_service
FP-KS12621C7	NH/NT855 Cylinder Kit .010 Head Gask Grommets	other_service
FS1692s	FUEL SOLENOID VALVE LOCATION	other_service
M-1808	DC CONTROL WIRING	other_service
TB11-29	Engine Monitor Board	other_service
TB11-30	Engine Monitor Board	other_service
TB11-31	Engine Monitor Board	other_service
234C134	3-Phase	phase
234C137	3-Phase	phase
234C140	Single Phase	phase
234C141	Single Phase	phase
305P240	Rectifier, Volt. Cont.Reactor (Incl.in Rect. & Resistor A: 305P218)	reactor
305P233	Rectifier Assy., Power (Incl. two #305P234 wire & hardware)	rectifier
305P234	Rectifier Assy., Power (Field) (Incl. in Rect. #305P218)	rectifier
3ISA78	Rectifier, Voltage Control	rectifier
307-2621-02	Relay, Start Solenoid (K4)	relay
3044125	15,000-Ohm, 25-W - For 220/380-V, 3-Phase, 4-Wire	resistor
304PA76	Resistor, Volt. Cont.Reactor (Incl.in Rect.& Resistor A: 305P218)	resistor
3058227	Resistor Assy., Rect, & Incl. (Incl.in Rect. & Resistor A: 305P218)	resistor
204493	Ring, Collector	ring
800-0092	Screw, Cap - Hex Head (1/2-13 x 1.5)	screw
DM-3010461	Crankshaft Rear Seal - NT855, NTC855	seal
193-0432	Sender, Oil Temperature (S2 Engine Block, E4 Oil Pan)	sensor
193-0447-01	Sender, Water Temperature (E2)	sensor
193-0448	Sender, Oil Pressure	sensor
309-0269	Switch, Low Engine Temperature (S4)	sensor
309-0576	Switch, Thermostat - High Engine Coolant Temperature (S2)	sensor
309-0641-07	Switch, Oil Pressure (Closes at 20 lbs. Descending)	sensor
960-0504	PCC Control Service Manual	service_manual
960-0507	Detector Control Service Manual	service_manual
191-1858	Starter (24VDC)	starter
3320645	Strip, Marker - Volt. Con. Reactor (9305P218)	strip
5208190	Stud, Fixed Resistor Mtg.	stud
23201396	Support, Gen. Mtg.	support
1S0A717	Switch Assy., Overspeed	switch
B-342-3s	PRIMING TURBOCHARGER OIL SUPPLY INLET LINE. DISCONNECT AT THIS POINT TO PRIME	turbocharger
302P421	Scale Reads 0-300	voltmeter
304A15	S Washer, Fixed Resistor Cent. to Alternator End Bell	washer
508-0292	Washer, Sealing - Copper	washer
526-0029	*Washer, Flat (1/2")	washer

Parts cataloged across all variants of this engine family — verify the exact part fits your specific variant and serial number before ordering.

Aftermarket parts that fit this engine

0327-1507 FridayParts $499.99 FP-XP-0041835

Parts listed by aftermarket suppliers as fitting this engine — leads compiled from supplier catalogs; verify the exact part for your serial number.

Common questions

What is the oil capacity of the Cummins/Onan NT855?

The Cummins/Onan NT855 engine has an oil capacity of 40.0 liters.

What is the displacement of the Cummins/Onan NT855?

The Cummins/Onan NT855 has a displacement of 8.55 liters with 6 cylinders.

Which generators use the Cummins/Onan NT855 engine?

The Cummins/Onan NT855 powers 7 generator set(s), including Cummins/Onan C350 D5, Cummins/Onan C350 D6, Cummins/Onan C400 D5, Cummins/Onan C400 D6, Cummins/Onan C440 D5.

How often should you change the oil in the Cummins/Onan NT855?

The Cummins/Onan NT855 oil change interval is every 100 hours.

What is a common problem with the Cummins/Onan NT855 engine?

A commonly reported issue on generators using the Cummins/Onan NT855 is: UNDER FREQUENCY. Fix: Shutdown.