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Cummins/Onan NTA855-G6 Engine

Name: Cummins/Onan NTA855-G6 Engine
Brand: Cummins/Onan

The Cummins/Onan NTA855-G6 is an engine. It powers generator sets from Cummins/Onan, including the 300 DFCB.

Also known as: Cummins NTA855-G6

Part of the Cummins/Onan NTA855 engine family — 9 variants share parts & fitment.

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

Engine specifications

Generator sets powered by this engine

Cummins/Onan 300 DFCB

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

Common problems

The FAULT 1 or FAULT 2 fault lamp lights. Engine shuts down immediately, engine runs for several seconds and then shuts down, or engine continues to run.
Cause: Standard undesignated fault functions are programmed to shut down the set when a fault is sensed. Fault 1 is time delayed while Fault 2 is immediate. The nature of the fault is an optional selection that is determined when the set installation is designed. The undesignated fault functions may also be programmed for non-shutdown or non-time delay.
SWITCH OFF lamp flashes.
Fix: Indicates Run/Stop/Remote switch is in the Stop position which will prevent automatic starting if an automatic transfer switch is used. Move the Run/Stop/Remote switch to the Remote position for automatic starting.
PRE LO OIL PRES lamp lights. Engine continues to operate.
Fix: Indicates engine oil pressure has dropped to 20 psi (138 kPa). If generator is powering critical loads and cannot be shut down, wait until next shutdown period and then follow step 5 procedure. If engine can be stopped, follow procedures in step 5.
PRE HI ENGINE TEMP lamp lights. Engine continues to operate.
Fix: Indicates engine has begun to overheat and engine temperature has risen to approximately 215°F (102°C). If generator is powering non-critical and critical loads and cannot be shut down, use the following: a. Reduce load if possible by turning off non-critical loads. b. Check air inlets and outlets and remove any obstructions to airflow. If engine can be stopped, follow procedure in step 3.
OVERCRANK lamp lights and engine stops cranking.
Fix: Indicates possible fuel system problem. a. Check for empty fuel tank, fuel leaks, or plugged fuel lines and correct as required. b. Check for dirty fuel filter and replace if necessary (see Maintenance section). c. Check for dirty or plugged air filter and replace if necessary (see Maintenance section). d. Reset the control and restart after correcting the problem. Contact an authorized service center for service if none of the above.
No AC output voltage.
Fix: Field breaker is tripped. Reset breaker. Contact an authorized service center if voltage buildup causes breaker to trip.
LO OIL PRES lamp lights. Engine shuts down.
Fix: Indicates engine oil pressure has dropped to 14 psi (97 kPa). Check oil level, lines and filters. If oil system is OK but oil level is low, replenish. Reset control and restart. Contact an authorized service center if oil pressure is not in the range of 25 to 40 psi (172 to 275 kPa).
LO FUEL LAMP lights. Engine shuts down and LO OIL PRES lamp lights.
Fix: Indicates engine has run out of fuel. Check fuel level and replenish as required.
LO FUEL lamp lights. Engine continues to run.
Fix: Indicates diesel fuel supply is running low. Check fuel supply and replenish as required.
LO ENG TEMP lamp lights. Set is in standby mode but is not operating.
Fix: Lamp lights when engine coolant temperature is 70° F (21° C) or lower. Since the lamp goes out after the engine warms up, there should be no cause for alarm even during initial generator set operation.
HI ENG TEMP lamp lights. Engine shuts down.
Fix: Indicates engine has overheated (engine temperature has risen above 222°F/106°C) or coolant level is low (sets with coolant level sensor). Allow engine to cool down completely before proceeding with the following checks: a. Check coolant level and replenish if low. Look for possible coolant leakage points and repair if necessary. b. Check for obstructions to cooling airflow and correct as necessary. c. Check for a slipping fan belt and tighten if loose. d. Reset control and restart after locating and correcting problem. Contact an authorized service center if none of the above.
Green RUN lamp lights following engine startup.
Fix: Indicates all engine systems are normal. No corrective action required.
Green RUN lamp does not light following engine startup.
Cause: Indicates possible Start/Disconnect relay failure.
Fix: Contact an authorized service center for assistance.
Fault lamp lights but no fault exists. Engine gauges show oil pressure, engine temperature, and frequency (speed) are within normal limits.
Fix: The monitor board or a sensor may be at fault. Contact an authorized service center for service.
Engine will not crank.
Cause: Indicates possible fault with control or starting system. Check for the following conditions:
Fix: A. Fault lamp on. Correct fault and reset control. b. Poor battery cable connections. Clean the battery cable terminals and tighten all connections. c. Discharged or defective battery. Recharge or replace the battery. d. Emergency stop button (if equipped) pushed in. To reset, pull switch out and move Run/Stop/Remote switch to Stop position. Then push test switch to Reset/Lamp position. e. Contact an authorized service center if none of the above.

Compiled from service & troubleshooting documentation across every generator set that uses the Cummins/Onan NTA855-G6.

Service intervals

Item	Action	Hours	Months	Notes
Crankcase oil	Change	50 hr		First service — Break-in: drain and replace crankcase oil after first 50 hours on new generator sets

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	Exhaust pipe clearance to combustible wall or partition	12	inches (305 mm)	minimum
Clearance	Exhaust thimble spacing	9	inch (230 mm)	minimum
Clearance	Vibration isolator base elevation variation	0.25	inch (6 mm)	shimmed or grouted
Clearance	Vibration isolator top plate to base clearance	0.25	inch (6 mm)	nominal, or greater
Other	Battery specific gravity	1.260	specific gravity	at 80 F (27 C)
Other	Breather cleaning compressed air	30	psi	maximum (OSHA)
Other	Control circuit wire size, distance 1000 to 2000 ft (305 to 610 m)	16	gauge stranded copper
Other	Control circuit wire size, distance less than 1000 ft (305 m)	18	gauge stranded copper
Other	Cooling air inlet size relative to radiator duct outlet	1-1/2	times larger	radiator cooled models
Other	Cycle cranking option	15-second crank, 15-second rest, 3 cycles
Other	Fuel pump maximum lift	5	ft (1.5 m)
Other	Fuel tank capacity for continuous full load operation	36	hours	minimum
Other	Load balance line current tolerance	10	percent of median value	with loads connected
Other	Mounting base surface above floor	6	inches (152 mm)	minimum for servicing
Other	Mounting bolt size	3/4	inch	anchored to floor
Other	Overcrank cranking limit (standard control)	75	seconds
Pressure	Air cleaner cleaning compressed air	30	psi (207 kPa)	maximum
Pressure	Engine oil pressure	40 to 60	psi (275 to 414 kPa)	at operating temperature
Pressure	Low oil pressure shutdown	14	psi (97 kPa)	below
Pressure	Lubrication system priming pressure	30	psi (207 kPa)	primer pump at filter housing
Pressure	Maximum allowable exhaust back pressure	40.8	in H2O (10.2 kPa)
Pressure	Normal oil pressure range	25 to 40	psi (172 to 275 kPa)
Pressure	Oil priming pressure while cranking	15	psi (103 kPa)	maintained for 15 seconds at filter head priming port
Pressure	Pre-low oil pressure alarm	20	psi (137 kPa)	or less
Speed	Governor droop adjustment range	zero % (isochronous) to 5%	percent speed droop
Speed	No-load governed speed, 50 Hz isochronous	1500	RPM (50.0 Hz)	no load
Speed	No-load governed speed, 50 Hz, 3% droop	1545	RPM (51.5 Hz)	no load
Speed	No-load governed speed, 50 Hz, 5% droop	1575	RPM (52.5 Hz)	no load
Speed	No-load governed speed, 60 Hz isochronous	1800	RPM (60.0 Hz)	no load
Speed	No-load governed speed, 60 Hz, 3% droop	1854	RPM (61.8 Hz)	no load
Speed	No-load governed speed, 60 Hz, 5% droop	1890	RPM (63.0 Hz)	no load
Speed	Overspeed shutdown, 50 Hz units	1850 +50	r/min
Speed	Overspeed shutdown, 60 Hz units	2100 +/- 90	r/min
Speed	Starter disconnect speed	450 to 570	RPM
Temperature	Heat exchanger engine coolant temperature range	165 to 195	°F (74 to 91 °C)	adjust raw water flow while viewing water temperature gauge
Temperature	High engine temperature shutdown	222	F (106 C)	above
Temperature	Low engine temperature (LET) alarm	70	F (21 C)	or lower
Temperature	Pre-high engine temperature alarm	215	F (102 C)
Temperature	Water (coolant) temperature	165 to 195	°F (74 to 91 °C)	depending on load and ambient temperature
Torque	Oil drain plug	60-70	ft-lb (81-95 N-m)
Torque	Oil filter housing plug	15 to 20	ft lb (20 to 27 N•m)
Voltage	AC voltage regulation	+/- 2	percent	no load to full load
Voltage	DC voltmeter reading	24 to 28	volts	while set is running
Voltage	Random voltage variation	+/- 1	percent	constant loads

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	Ethylene glycol base permanent antifreeze				Precharge coolant filter compatible with plain water and ethylene glycol base coolants; refer to engine manufacturer for methoxy propanal base antifreeze.
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
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	ASTM No. 2 Diesel				Alternate diesel fuels allowed within engine manual specifications. Do not use galvanized or copper lines, fittings or fuel tanks.
Fuel	No. 2 diesel (No. 1 acceptable)				Filter or strain fuel as tank is filled; keep tanks full to avoid condensation

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
FAULT 1	FAULT 1 (red) lamp	Undedicated fault; may be field programmed as shutdown or non-shutdown, timed or non-timed (normally timed shutdown)	Shutdown	Determine nature of fault per installation design
FAULT 2	FAULT 2 (red) lamp	Undedicated fault with same features as Fault 1 (normally timed shutdown)	Shutdown	Determine nature of fault per installation design
HI ENG TEMP	HI ENG TEMP (red) lamp	Engine has shut down because of critically high engine temperature (above 222 F/106 C) or low coolant level	Shutdown	Allow to cool; check coolant level, cooling airflow and fan belt; reset and restart
LO FUEL	LO FUEL (yellow) lamp	Fuel supply is marginally low; if set shuts down with LO OIL PRES, engine has run out of fuel	Warning	Check fuel supply and replenish as required
LO OIL PRES	LO OIL PRES (red) lamp	Engine has shut down because of critically low oil pressure (below 14 psi/97 kPa)	Shutdown	Check oil level, lines and filters; replenish oil; reset and restart; verify pressure 25 to 40 psi (172 to 275 kPa)
LOW ENG TEMP	LOW ENG TEMP (yellow) lamp	Engine temperature is marginally low for starting; may indicate inoperative coolant heater (lights at 70 F/21 C or lower)	Warning	Check coolant heater power supply, fuse and cord; check coolant level and leakage
OVERCRANK	OVERCRANK (red) lamp	Engine has failed to start during the cranking period (75-second limit; cycle cranking 3 x 15 seconds)	Shutdown	Place switch in STOP and press Reset; wait two minutes and retry; check fuel supply, fuel filter and air filter
OVERSPEED	OVERSPEED (red) lamp	Engine has shut down because of excessive speed (60 Hz set at 2100 +/- 90 r/min, 50 Hz set at 1850 +50 r/min)	Shutdown	Contact an authorized service center for service
PRE HI ENG TEMP	PRE HI ENG TEMP (yellow) lamp	Engine temperature is marginally high (approximately 215 F/102 C)	Warning	Reduce load; check air inlets/outlets and remove obstructions
PRE LO OIL PRES	PRE LO OIL PRES (yellow) lamp	Engine oil pressure is marginally low (20 psi/137 kPa or less)	Warning	Find and correct cause as soon as possible
RUN	RUN (green) lamp	Comes on when starter circuit opens after set starting; all engine systems normal	Info	No corrective action required
SWITCH OFF	SWITCH OFF (flashing red) lamp	Generator set is not in automatic start mode (Run/Stop/Remote switch in Stop position)	Info	Move Run/Stop/Remote switch to Remote position for automatic starting

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

Procedures

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.

Battery Connections installation

⚠ Ignition of explosive battery gases can cause severe personal injury; always connect battery negative last.

⚠ Do not smoke while servicing the batteries.

Use two, 12 volt (Type 8D) batteries for a normal installation.
Connect batteries in series: negative post of first battery to positive post of second.
Connect the negative (–) battery cable last to prevent arcing.
If no built-in charge circuit exists, connect a separate trickle or float charger.

Connecting the Load installation

⚠ Do not connect generator set directly to any building electrical system; connect only through an approved isolation switch or paralleling device.

Bolt load wires to the appropriate terminals on the generator terminal block.
Terminals are stamped U, V, W and N (U, V, W = L1, L2, L3; N = L0).
Route generator output leads through current transformers CT21, CT22 and CT23 for meter operation.
Balance loads so current from each line terminal is about the same.
Ensure each line current is within 10 percent of median value and below nameplate rating.

Prestart Preparation Checks installation

⚠ Verify at least 12 inches (305 mm) clearance between exhaust pipes and combustible materials.

Check ventilation and exhaust systems.
Check all mechanical connections.
Fill the coolant, lubrication and fuel systems.
Prime the lubrication and fuel systems.
Check the fuel system for leaks.
Check the lubrication system for leaks.

Vibration Isolators Installation and Adjustment installation

Tools: Leveling bolt, Lock nut

Place isolators on support structure; shim or grout so all bases are within 0.25 inch (6 mm) elevation.
Loosen side snubber lock nuts so top plate is free to move vertically and horizontally.
Place genset onto isolators, aligning skid mounting with threaded isolator hole.
Insert leveling bolt through skid into isolator to adjust clearance.
Turn leveling bolt until nominal 0.25 inch (6 mm) or greater clearance is achieved.
Adjust leveling bolts until set is level and sufficient clearance remains.
Lock leveling bolts in place with lock nut.
Snubber nuts may remain loose to provide better isolation.

Air Cleaner Service maintenance

⚠ Handle filters with care; install recommended replacement part if damaged.

Loosen fasteners and remove air cleaner housing end cap.
Remove air filter element from filter housing.
Blow low pressure compressed air (30 psi/207 kPa) through element from clean side.
Hold nozzle at least 1 inch (25 mm) away to avoid damage.
Soak filter at least 15 minutes in water and Donaldsons D1400 solvent.
Rinse with clean water, air dry, reinstall; replace after two cleanings.

Coolant Filter Service maintenance

⚠ Do not use antifreeze with an anti-leak formula.

Close the shutoff valves.
Unscrew coolant filter and discard.
Apply a light coat of lubricating oil to the gasket surface.
Install new filter; tighten by hand until seal touches head, then 1/2 to 3/4 turn.
Open the shutoff valves.

Cooling System Fill and Air Purge maintenance

⚠ Do not open a radiator or heat exchanger pressure cap while the engine is running.

Remove the radiator pressure cap and monitor the coolant level on first start.
Add coolant as trapped air is expelled and the level drops.
Replace the pressure cap when the coolant level is stable.

Crankcase Breather Service maintenance

Remove wing nut, flat washer and rubber washer; lift cover and swing away.
Lift out breather element, vapor element and gasket.
Clean all parts with approved solvent; dry with compressed air 30 psi max.
Inspect all parts and replace if necessary.
Reassemble filter assembly, replace cover and secure.

Filling the Cooling System (Standard Radiator and Heat Exchanger Sets) maintenance

⚠ Contact with hot coolant can result in serious burns.

Remove the cooling system pressure cap.
Fill system with water or water/antifreeze mixture.
Start engine and monitor coolant level with cap removed.
Add coolant as trapped air is expelled.
Replace pressure cap when coolant level is stable.

Flushing and Cleaning the Cooling System maintenance

⚠ Excessive air pressure could split the radiator core; apply gradually.

⚠ De-energize engine coolant heater before flushing and cleaning.

Tools: Flushing gun

Clean system with sodium bisulphate or oxalic acid per supplier instructions.
Neutralize and flush with clean water.
Open upper and lower radiator hose connections and install radiator cap.
Attach flushing gun to lower hose; let water run until radiator is full.
Apply air pressure gradually; repeat until water is clean.
Remove thermostat; flush engine block until water runs clean.
Replace thermostat and all hoses; refill cooling system.

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 NTA855 family

Part #	Description	Category
122-0526	Bypass Hood, Air Inlet (Used on Heavy Duty Air Cleaner)	air_filter
140-1346	Air Cleaner (Includes Element)	air_filter
140-2391	Element - Air Cleaner (Standard)	air_filter
140-2392	Element, Air Cleaner - Primary	air_filter
140-2393	Element, Air Cleaner - Safety	air_filter
M-1398	STANDARD AIR CLEANER	air_filter
M-1398-2	HEAVY DUTY AIR CLEANER (OPTIONAL)	air_filter
M-1398-1	DUCT	air_inlet
511-0084	Belt, Charging Alternator	belt
511-0160	Belt, Drive - V (Fan)	belt
319-2236	Bracket, Mounting	bracket
B-342-10	CRANKCASE BREATHER	breather
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
130-3537	Filter, Water - W/Corosion Inhibiting Chemical DCA4	coolant_filter
130-3541	Filter, Water - w/Corrosion Inhibiting Chemical DCA4 (Pre-Charging)	coolant_filter
CS-1075-1	COOLANT FILTERS	coolant_filter
0300-4623-09	DFCB (600V)	current_transformer
0300-4623-10	DFCC (600V)	current_transformer
0300-4623-24	DFCB BR (0-480V)	current_transformer
0300-4623-27	DFCC BR (0-480V)	current_transformer
ES-1779-1	VOLTAGE REGULATOR AND EXCITATION SWITCH	excitation_switch
CS-1130-1	EXPANSION TANK CAP	expansion_tank_cap
M-1740	SUPPLY LINE, FILTER TO INJECTION PUMP FS-1424	fuel_pump
155-2287-02	Gasket, Flange (used with 155-2281 Elbow)	gasket
501-0551	Line, Fuel - Flexible (Bypass line)	hose
503-1467-07	Hose, Rubber (3/4" ID x 33" LG) Radiator to Filter Housing	hose
503-1679-02	Hose, Rubber - Upper	hose
505-1414-01	Hose, Rubber - Lower	hose
M-1739	CYLINDER BLOCK RADIATOR DRAINCOCK AND OIL COOLER AND LOWER RADIATOR HOSE M-1739	hose
122-0755	Lube & Bypass Filter (Latest Style Used In Engine Manufacturing)	oil_filter
LF3000	Lube, Spin-On	oil_filter
M-1298	CHECK OIL LEVEL (ON RIGHT SIDE OF ENGINE)	oil_filter
100-1359	Engine, Replacement (Cummins NTA855G)	other_service
102-1335	Plug, Oil Drain	other_service
309-0437	(222"F)	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
903-0124	NA	other_service
903-0204	NA	other_service
903-0500	NA	other_service
903-0604	NA	other_service
960-0138		other_service
960-0606		other_service
S-1610	VOLTAGE SELECTOR LIGHTS	other_service
307-2621-02	Relay, Start Solenoid (K4)	relay
800-0092	Screw, Cap - Hex Head (1/2-13 x 1.5)	screw
151-0411	Pickup, Magnetic	sensor
193-0244	Sender, Pressure - 0i1	sensor
193-0375	# Sender, Water Temperature	sensor
193-0432	Sender, Oil Temperature (S2 Engine Block, E4 Oil Pan)	sensor
309-0179	'Switch, Thermostatic - Hi Engine Coolant Temperature	sensor
309-0269	Switch, Low Engine Temperature (S4)	sensor
333-0407	Switch, Pressure - Oil, 14# PSI (SHUTDOWN) With Dual Terminals	sensor
960-0504	PCC Control Service Manual	service_manual
960-0507	Detector Control Service Manual	service_manual
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.

Common questions

Which generators use the Cummins/Onan NTA855-G6 engine?

The Cummins/Onan NTA855-G6 powers 1 generator set(s), including Cummins/Onan 300 DFCB.

What is a common problem with the Cummins/Onan NTA855-G6 engine?

A commonly reported issue on generators using the Cummins/Onan NTA855-G6 is: The FAULT 1 or FAULT 2 fault lamp lights. Engine shuts down immediately, engine runs for several seconds and then shuts down, or engine continues to run.. Cause: Standard undesignated fault functions are programmed to shut down the set when a fault is sensed. Fault 1 is time delayed while Fault 2 is immediate. The nature of the fault is an optional selection that is determined when the set installation is designed. The undesignated fault functions may also be programmed for non-shutdown or non-time delay..