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Cummins/Onan 6BT5.9-G6 Engine

Name: Cummins/Onan 6BT5.9-G6 Engine
Brand: Cummins/Onan

The Cummins/Onan 6BT5.9-G6 is a 5.88 L 6-cylinder turbocharged engine rated at 1500 rpm, producing up to 140 kW. It powers generator sets from Cummins/Onan, including the C110D6, C120D5 and DGDB. It holds 100 L (26.4 gal) of oil and 100 L (26.4 gal) of coolant.

Also known as: Cummins 6BT5.9-G6

Part of the Cummins/Onan 6BT5.9 engine family — 5 variants share parts & fitment.

5.88 L

Displacement

Cylinders

1500 rpm

Rated speed

140 kW

Gross power

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

Engine specifications

Oil capacity	100.0 L
Coolant capacity	100.0 L
Displacement	5.88 L
Cylinders	6
Aspiration	Turbocharged
Rated speed	1500 rpm
Gross power	140 kW

Generator sets powered by this engine

Cummins/Onan C110D6 Cummins/Onan C120D5 Cummins/Onan DGDB

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

Common problems

Over Current 1471
Low Coolant Level 197
Weak Battery 1442
Under Frequency 1448
Too Long in Idle 2342
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.
Fix: The 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.
Status Indicators Fault Code Table
Speed/Hz Match 1469
Speed Signal Lost 121
Shutdown After Battle Short 1123
Short Circuit 1445
Same features as Fault 1 (Normally set for timed shutdown). FAULT 2
Remote Emergency Stop 1434
Pre-Low Oil Pressure Sensor 143

Compiled from service & troubleshooting documentation across every generator set that uses the Cummins/Onan 6BT5.9-G6.

Maintenance schedule

Item	Spec	Capacity	Part #
Air filter	Normal duty air filter.		—
Fuel filter	Oil and fuel filter fitted, water separator.		—
Oil filter	Oil and fuel filter fitted, water separator.		—
Battery	460 amps minimum at ambient temperature of 32°F (0°C)		—
Belt	N/A		—
Coolant	Coolant capacity (engine and radiator)	24.6 l	—
Oil	Lubrication system oil capacity	16.4 l	—
Spark plug	N/A		—

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
Coolant Heater	Check	50 hr		Verify hot coolant is being discharged from the outlet hose.
Coolant Level	Check	8 hr
Coolant Level (Recovery Tank)	Check	8 hr		Table 5-1
Exhaust Condensate Trap	Drain	8 hr		Table 5-1
Fuel Level	Check	8 hr		Table 5-1
Fuel Tanks (water and sediment)	Drain	8 hr		Drain 1 cup or more of fuel to remove water and sediment.
General Genset Inspection	Inspect	8 hr		Table 5-1; also indicated for weekly/50 hours (X1, X2)
Inspect Genset	Check	8 hr		Check for oil, fuel, cooling and exhaust system leaks. Check exhaust system audibly and visually with set running and repair any leaks immediately.
Oil Level	Check	8 hr		Table 5-1
Water and Sediment from Fuel Tank	Drain	8 hr		Table 5-1; drain 1 cup or more of fuel to remove water and sediment
Air Cleaner	Clean	50 hr		Table 5-1; X3 perform more often in dusty conditions
Battery Charging System	Check	50 hr		Table 5-1
Charge Air Piping	Check	50 hr		Table 5-1
Crankcase Oil	Drain	50 hr		First service — Break-in: drain and replace the crankcase oil after the first 50 hours of operation on new generator sets.
Engine oil and filter	Change	50 hr		First service — Drain and replace crankcase oil after first 50 hours on new generator sets
Starting Batteries	Check	50 hr		Table 5-1
Battery Electrolyte Level	Check	200 hr		Check at least every 200 hours of operation; disregard for maintenance-free battery
Anti-freeze and DCA Concentration	Check	250 hr	6 mo	Table 5-1
Coolant Filter	Change	500 hr	6 mo	Table 5-1
Cooling System	Clean	500 hr	6 mo	Table 5-1
Crankcase Breather	Clean	500 hr	6 mo	Table 5-1
Crankcase Oil and Filter	Change	250 hr	12 mo	Table 5-1 X6: if genset is used for standby applications, change oil every 12 months or 250 hours, whichever comes first
Drive Belt Tension	Check	250 hr	6 mo	Visually check belt for evidence of wear or slippage. Replace if hard or brittle. Refer to engine operation and maintenance manual.
Fuel Filter(s)	Drain	250 hr	6 mo	Table 5-1
Fuel Filters	Change	250 hr	6 mo	Table 5-1
Governor Adjustment	Check	250 hr	3 mo
Radiator Hoses for Wear & Cracks	Check	250 hr	6 mo	Table 5-1
Generator bearing	Inspect	1000 hr		Inspect for wear every 1000 hours by an Onan Distributor
Valve Lash	Adjust	1000 hr		Table 5-1: after 1000 hours; contact an authorized service center for service
Generator bearing	Replace	10000 hr	24 mo	Prime power: every 10,000 hours or after two years; standby power: every five years
Air cleaner element	Change	500 hr	12 mo	Yearly or sooner if service indicator pops up
Generator Set Exercise	Test		1 mo	Exercise the generator set at least once a month for a minimum of 30 minutes, under not less than 30 percent of the nameplate rating

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	Clearance around generator set for maintenance and service access	1	meter (3 feet)
Clearance	Exhaust pipe clearance from combustible wall or partition	12	inches (305 mm)	minimum
Clearance	Float switch lift below C-clip stop	1/8	inch (3 mm)
Clearance	Fuel line clearance from electrical wiring	1/2	inch (12.7 mm)	minimum
Clearance	Fuel line clearance from hot exhaust parts	2	inch (51 mm)	minimum
Clearance	Overspeed switch magnet-to-fly arm air gap (minimum)	0.005	inches (0.13 mm)
Clearance	Vibration isolator base elevation (max difference between isolator bases)	0.25	inch (6 mm)
Clearance	Vibration isolator top plate to base clearance	0.25	inch (6 mm)	nominal, minimum
Gap	Mechanical overspeed switch air gap between magnet and fly arm (replace switch if less)	0.005	inches (0.13 mm)
Other	AVR DROOP preset at factory	five percent droop at full load and zero power factor
Other	Battery electrolyte corrected specific gravity (fully charged)	1.260		electrolyte temperature corrected
Other	Battery electrolyte specific gravity (fully charged)	1.260	specific gravity	corrected to 80 F (27 C)
Other	Battery electrolyte specific gravity charge threshold	1.215	specific gravity	charge battery if reading is below this value
Other	Battery recharge threshold specific gravity	1.215
Other	Battery specific gravity recharge threshold	1.260	specific gravity	recharge if below
Other	Battery specific gravity temperature correction	four gravity points (0.004) for every ten degrees above 80 F (27 C)
Other	Battery specific gravity, fully charged	approximately 1.260	at 80°F (27°C)
Other	Cool-down at idle	0−30	min
Other	Coolant level below radiator cap opening	2	inches
Other	Customer output relay contacts rating (TB1 outputs 1-4)	2	amps at 30 VDC	normally open contacts
Other	Cycle crank crank and rest time	7 to 20	seconds
Other	Cycle crank number of cycles	3, 4, or 5
Other	Cycle cranking option	15	seconds	15 s crank, 15 s rest, 3 cycles
Other	Default start cycles	3	cycles	15 seconds of cranking and 15 seconds of rest
Other	ECM fuse F1 (starter solenoid circuit)	20	amps
Other	ECM fuse F2 (fuel solenoid circuit)	20	amps
Other	ECM fuse F3 (continuous B+ to remote circuits)	15	amps
Other	ECM fuse F4 (ECM circuits)	5	amps
Other	ECM fuse F5 (engine gauge circuits)	5	amps
Other	Frequency Adjust range	5	percent of nominal frequency	e.g. 60.0 Hz adjustable 57.0 to 63.0 Hz
Other	Frequency adjustment range	±5%	%	genset running
Other	Fuse A31-F1 (control B+)	5	Amp	Engine Interface board
Other	Fuse A31-F3 (auxiliary B+)	5	Amp	Engine Interface board; panel lights, run and start relays
Other	Fuse A38-F1 (Network B+)	10	Amp	Governor Output Module
Other	Fuse A38-F2 (Switched B+)	10	Amp	Governor Output Module
Other	Fuse A38-F3 (Governor B+)	10	Amp	Governor Output Module
Other	Fuse TB-Bat F1 (Customer B+)	20	Amp	Engine Harness Assembly
Other	GOV RAMP adjustment range	0 through 10	seconds
Other	Governor droop adjustment range	within 5	percent of nominal frequency (3 Hz for 60Hz sets, 2.5 Hz for 50Hz sets)
Other	Low oil pressure / high engine temperature fault time delay	about 10	seconds	following starter disconnect and inhibited during cranking
Other	Mounting bolts used to secure vibration isolators to base	5/8 inch or 16 mm		anchored mounting bolts
Other	Optional control relay (K11, K12, K13) contacts rating	10	amps at 600 VAC
Other	Overcrank cranking limit	75	seconds	standard overcrank control
Other	Overcrank limit (Sentinel)	60	seconds
Other	Overcrank option limit (Detector)	75	seconds
Other	Overspeed warning range 60 Hz sets	2000 to 2200	RPM
Other	REG VHZ adjustment range	1 through 50 (normal range 7 through 21)
Other	Rated To Idle delay	0−10	sec	Beginning Version 2.303; default = 0
Other	Response jumper setting - 90 to 550 kW	B to C
Other	Response jumper setting - over 550 kW	A to B
Other	Response jumper setting - under 90 kW	A to C
Other	Setup/calibration menu access code	574
Other	Specific gravity correction factor	0.004	gravity points	per 10 degrees electrolyte temperature above 80 F (27 C)
Other	Standard cycle cranking (Detector)	three 15-second cranking cycles with two 15-second rest periods
Other	Start delay adjustment range	0 to 300	seconds	remote starting in Auto mode
Other	Stop delay adjustment range	0 to 600	seconds	remote stopping in Auto mode
Other	Time Delay To Start	0−300	sec	default = 0
Other	Time Delay To Stop (Stop Delay)	0−600	sec	default = 0
Other	Trailer brake shoe adjustment back-off	10	clicks
Other	Trailer surge brake actuator stroke length (service brakes if exceeds)	1	inch (25 mm)

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		soft water/E.G./DCA mixture			Installation review checklist item: cooling system must be filled with soft water/E.G./DCA mixture.
Coolant	50/50 mix of water and antifreeze	Balanced coolant mixture of water, antifreeze and coolant additives			Drain and replace the mixture every 6 months or after 500 hours of operation. Do not add cold coolant to a hot engine; allow engine to cool below 120 F (50 C) before adding coolant.
Coolant	Water/antifreeze mixture				Permanent type antifreeze mixed per supplier for lowest expected ambient; do not use anti-leak additives
Engine oil		Refer to Cummins engine Operation and Maintenance Manual for lubricating oil recommendations/specifications		16.0 L	Oil capacity with filters 17 Qts (16 L); gensets are shipped with oil added
Engine oil	5W (Synthetic Oil)	API CC/CD, sulphated ash max 1.85%	below -23°C		Below -10 F (-23 C) and below; pour point 9 F (5 C) below lowest expected temperature
Engine oil	10W-30	API CC/CD	-23°C to -10°C		-10 F (-23 C) to 14 F (-10 C)
Engine oil	15W-40	API CC/CD	above -10°C		14 F (-10 C) and above
Engine oil	20W-40	API CC/CD	above 0°C		32 F (0 C) and above
Fuel	ASTM No. 2 diesel fuel				Cummins engines normally use ASTM No. 2 diesel fuel; will operate on alternate diesel fuels within specifications in Cummins engine Operation and Maintenance Manual.
Fuel	No. 2 diesel				No. 1 fuel or similar acceptable; consult engine manufacturer for non-standard fuel
Fuel	diesel				Do not use zinc coated or copper fuel lines with diesel fuel.
Hydraulic oil	DOT-3				Trailer master cylinder reservoir - keep at least half full

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; generator build-up is inhibited and engine governed at 800 RPM.	Warning	Remove ground from the engine idle input to return to normal speed and voltage.
102	EMERGENCY STOP	Indicates local or remote Emergency Stop.	Shutdown	Pull the button out; move the Run/Off/Auto switch to Off; press the Reset switch; select Run or Auto as required. Can only be reset at the PCC front panel.
1122	Rated/Idle Trans	Rated/Idle transition	Info
1123	Shutdown After Battle Short	Shutdown after Battle Short	Shutdown	Review Fault History and perform corrective action.
1124	Delayed Shutdown	Delayed shutdown	Warning	Review Fault History and perform corrective action.
1131	Battle Sh Active	Control is in Battle Short mode (bypasses several critical fault shutdowns).	Warning	When Battle Short mode is enabled, the Warning status indicator is lit along with displayed fault code 1131. Refer to Battle Short Mode description in Section 3.
121	Speed Signal Lost	Speed signal lost	Shutdown	Restart and check RPM on digital display; inspect MPU wires/connector pins; check for 3.5 to 15 VAC at MPU while cranking.
1311	Customer Input #1	Customer input #1 (optional customer selection)		Programmable (service tool): enable/disable input (default enable); status, warning or shutdown (default #1 = None); active closed or open (default closed [ground]); change display name up to 19 characters.
1311, 1312, 1317, 1318	CUSTOMER INPUT #1 - #4	Optional customer-selected fault input is active.		Disconnect signal lead from TB1 and reset the control; check external wiring/active input selection.
1312	Customer Input #2	Customer input #2 (optional customer selection)		Programmable (service tool): enable/disable input (default enable); status, warning or shutdown (default #2 = Warning); active closed or open (default closed [ground]); change display name.
1313−1316	Network Fault 1 thru 4	Network fault 1 through 4
1317	Customer Input #3	Customer input #3 (optional customer selection)		Programmable (service tool): enable/disable input; status, warning or shutdown; active closed or open; change display name.
1318	Customer Input #4	Customer input #4 (optional customer selection)		Programmable (service tool): enable/disable input; status, warning or shutdown; active closed or open; change display name.
1334	Crit Scaler Out Of Range	Incorrect feature or calibration was entered into control.	Shutdown	Reload correct feature/calibration file.
1335	Noncrit Scaler Out Of Range	Non-critical scaler out of range	Warning	Reload correct feature/calibration file.
1337	No Message	No message	Info
135	Oil Pressure Sensor H	Oil pressure sensor high	Warning	Check sender/connectors/wires; verify fault simulation not enabled; check 0.5 to 4.5 VDC at P7-13 (OP OUT) and P7-17 (OP COM).
141	Oil Pressure Sensor L	Oil pressure sensor low	Warning	Check sender/connectors/wires; check for shorts/open circuits at P7-13, 17, 21.
1416	Fail To Shutdown	Genset continues to run after receiving shutdown command (Battle Short feature enabled).	Warning	Refer to Battle Short Mode description in Section 3.
1417	Powr Down Error	The controller cannot power down because of some unknown condition; possible drain on battery	Warning	Contact an authorized service center for service.
143	Pre-Low Oil Pres	Engine oil pressure has dropped below the warning trip point	Warning	If generator is powering critical loads and cannot be shut down, wait until the next shutdown period and then follow code 415 procedure.
1433	Emergency Stop	Local Emergency Stop.	Shutdown	Pull the button out; move switch to O; press Fault Acknowledge/Reset; select Manual or Auto.
1434	Remote E-Stop	Remote Emergency Stop.	Shutdown	See code 1433 to reset.
1435	Low Coolant Temp	Initiates a warning when the engine jacket water coolant temperature falls below 70 deg F (21 deg C); provided to meet NFPA 110 requirements, in conjunction with illumination of the Warning LED.	Warning	Indicates engine coolant heater is not operating or is not circulating coolant. Check coolant heater connection to power supply: check for blown fuse or disconnected heater cord and correct. Check for low coolant level and replenish if required; look for possible coolant leaks and repair.
1438	Fail To Crank	Possible fault with control, speed sensing or starting system	Shutdown	Test for B+ at the starter; check fuse F3 (2 Amps); check K4 start pilot relay and starter circuitry; refer to code 121.
144	Coolant Sensor High	Engine coolant temperature signal is shorted high.	Warning	Check sender/connectors/wires; check resistance between P7-30 (IH20) and P7-34 (IH20 COM).
1442	Weak Battery	During cranking, 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	kW overload	Warning	Check load and load lead connections; check CTs and CT connections.
1445	Short Circuit	Short circuit	Shutdown	Check load and load lead connections (fault may not reset for several minutes).
1446	High AC Voltage	Phase voltage exceeded 130% of nominal, or 110% of nominal for 10 seconds.	Shutdown	Check fault simulation; clear fault and restart; refer to Generator/Base Board Isolation Procedure.
1447	Low AC Voltage	Phase voltage dropped below 85% of nominal for 10 seconds.	Shutdown	Check load; reconnect per reconnection diagram; check PMG/field wiring; check P8-21/P8-22 shunt connections.
1448	Under Frequency	Under frequency	Shutdown	Check fuel supply, intake air supply and load; check P8 connections.
1449	Over Frequency	Over frequency	Warning	Check fuel or air delivery problem; repair P7/P8 connections.
145	Coolant Sensor Low	Engine coolant temperature signal is shorted low.	Warning	Check sender/connectors/wires; check for shorts at P7-30 and P7-34.
1452	Gen CB Not Close	Genset circuit breaker (S2) failed to close when PTC enabled.	Warning	Refer to Section 5.
1453	Gen CB Not Open	Genset circuit breaker (S2) failed to open when PTC enabled.	Warning	Refer to Section 5.
1459	Reverse Power	Reverse power	Shutdown	Check wiring to voltage sense circuit; refer to CT Installation in Section 6.
146	Pre-High Coolant Temp	Engine is operating near cooling system capacity	Warning	Reduce load; check air inlets/outlets and remove obstructions to airflow; if engine can be stopped follow code 151.
1461	Loss Of Field	Loss of field (electric) due to reverse kVAR.	Shutdown	Check field circuit.
1466	Modem Failure	Modem failure	Warning	Check for open, short circuit to ground, and loose connections to the modem.
1468	Network Error	Network error	Warning	Refer to the LonWorks Network publications.
1469	Speed/Hz Match	Speed/Hz match	Shutdown	Check calibration file.
1471	Over Current	Over current	Warning	Check load and load lead connections.
1472	Over Current	Over current	Shutdown	Check load and load lead connections (fault may not reset for several minutes).
151	High Coolant Temp	Engine has overheated (coolant temperature has risen above the shutdown trip point)	Shutdown	Allow engine to cool; check coolant level; check airflow obstructions; check fan belt; check blower fan/remote radiator pumps; reset control and restart.
197	Low Coolant Level	Engine coolant level has fallen below the warning trip point.	Warning	If generator is powering critical loads and cannot be shut down, wait until next shutdown period, then 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 and follow 201-SHUTDOWN procedure; check oil pressure via menu prior to clearing fault.
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. Oil pressure limits in Table 4-3.
204	OIL PRESS SENDER	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.
210	LOW COOLANT TEMP	Warning occurs when engine coolant temperature is 70°F (21°C) or lower, indicating the engine coolant heater is not operating or is not circulating coolant.	Warning	Indicates engine coolant heater is not operating or is not circulating coolant; check coolant heater power supply/fuse, low coolant level, and open heater element.
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) prime.	Warning	Reduce load if possible; check air inlets/outlets; follow 212-SHUTDOWN procedure if engine can be stopped.
212	Oil Temp Sensor H	Oil temperature sensor high	Warning	Check sender/connectors/wires; check resistance between P7-22 (OIL TEMP) and P7-26 (OIL TEMP COM).
213	Oil Temp Sensor L	Resistance of the coolant temperature sender is out of range.	Warning	Check the resistance of the sender; should be 500 to 2k ohms.
214	LOW COOLANT LVL	Indicates engine coolant level has fallen below the trip point.	Warning	Check coolant level in radiator and coolant recovery bottle; look for leakage; reset control and restart.
215	LOW COOLANT LVL	Indicates engine coolant level has fallen below the trip point. LOW COOLANT LVL Shutdown will not occur if genset is in Idle mode (low coolant warning only).	Shutdown	Check coolant level in radiator and recovery bottle and replenish if low; check defective coolant bottle hose or radiator cap; reset control and restart after correcting problem. Will not occur in Idle mode.
220	MAG PICKUP	Mag pickup speed indication is not being sensed or does not match generator set output frequency.	Shutdown	Restart and check RPM on the digital display; isolate per troubleshooting table 4-18.
221	FAIL TO CRANK	Possible fault with control or starting system; engine will not crank.	Shutdown	Check fuse F3 on the Engine Interface board; clean battery cable connections; recharge or replace battery.
222	OVERCRANK	Possible fuel system problem; engine stops cranking.	Shutdown	Check for empty fuel tank, fuel leaks, or plugged fuel lines; check/replace dirty fuel filter and air filter; reset and restart.
223	OVERSPEED	Indicates engine has exceeded normal operating speed (115% ±1% of nominal).	Shutdown	Inspect the mechanical fuel linkage and repair or replace; check the EFC for binding or damage; monitor the PCC duty cycle display and replace A32 or A38 as indicated.
224	FAIL TO SYNCHRONIZE	The generator set has not synchronized to the system bus within the allowable time frame.		Check governor system stability and adjust governing/synchronizer parameters; check for fuel system problems causing engine instability; widen synchronizing window and reduce acceptance time delay.
226	FAIL TO CLOSE	Indicates that the paralleling breaker has been given a signal to close, but has not closed properly.		Verify charging mechanism of paralleling breaker; check the close signal to the breaker; verify auxiliary contact signals from the breaker to the control are operational.
230	LOW DC VOLTAGE	Indicates battery voltage is below 10 VDC.	Warning	Recharge or replace battery; clean/tighten connections; check engine DC alternator; check battery charger float level.
231	HIGH DC VOLTAGE	Indicates battery voltage exceeds 32 VDC.	Warning	Check voltage float level on battery charger if applicable (lower float level); check engine DC alternator and replace if normal battery charging voltage is not obtained.
232	WEAK BATTERY	Indicates battery voltage drops below 60% of nominal for two seconds, during starting.	Warning	Recharge or replace the battery; see 230 LOW DC VOLTAGE.
2323−2326	Network Fault 5 thru 8	Network fault 5 through 8
2327	PTC Fault	PTC module or communication link not working properly when PTC enabled.	Warning	Check blinking light on PTC module; check B+ TB3-3 to TB3-4; check PTC status voltage TB3-5 to TB3-6 (~0.2 VDC); repower control.
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	Repower PCC 2100 control to clear; check S1 AC inputs at TB5; check S1 pickup/dropout set points.
2335	Excitation Fault	Loss of all three voltage sense leads or failure in excitation circuit.	Shutdown	Critical shutdown fault; suspends Battle Short and shuts down immediately.
2336	Memory Error	Memory error	Shutdown	Try reloading calibration file.
2337	Pwr Tran Disabled	Power transfer disabled	Warning	Use InPower to enable PTC feature; cycle power off for 5 seconds then repower.
2338	Pwr Tran Failure	Power transfer failure	Warning	Check blinking light and B+ TB3-3 to TB3-4; check connections between TB2 and TB3; cycle power.
2339	Pwr Down Enabled	Power down enabled	Warning	None required.
234	Overspeed	Overspeed shutdown	Shutdown	Critical shutdown fault; suspends Battle Short and shuts down immediately.
2341	High Control Temp	High control temperature	Warning	Check genset room air flow.
2342	Too Long In Idle	Genset has been in Idle mode too long.	Warning	Exit idle mode.
235	Low Coolant Level	Engine coolant level has fallen below the shutdown trip point.	Shutdown	Check coolant level and replenish; look for leaks; reset control and restart.
2358	High S1 Voltage	Utility (S1) voltage increased above over voltage threshold.	Warning	Measure S1 AC inputs at PTC module; check utility nominal voltage; check sensor set points.
2396	S1 CB Not Close	Utility contact (S1) failed to close with PTC enabled.	Warning	Refer to Section 5.

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

Procedures

Adjusting Default Settings (Controller Configuration Menu) adjustment

Make sure Main Menu 1 is displayed and simultaneously press the Home Menu and Previous Main Menu buttons.
Press the buttons next to the and symbols to navigate between the three submenus.
Press the button next to the symbol until the + and − symbols are displayed.
Press the button next to the + or − symbol to select the desired option.
Press the symbol to save the changes.

Adjusting Values/Parameters (Adjust Menu) adjustment

⚠ If the Home button or Previous Main Menu button is pressed before pressing the save symbol, the changes are not saved.

⚠ Long periods of engine idling can eventually affect engine performance and may void engine warranty.

Press the button next to the symbol in the display until the + and − symbols are displayed.
If necessary, press the button next to the or symbols to move to the numeric character you wish to change.
Press the button next to the + symbol to increase the value; press the button next to the − symbol to decrease the value.
After adjusting, press the symbol to save; make sure the cursor is on the last numeric character before pressing.

Adjusting Values/Parameters (PowerCommand 2100 Control) adjustment

Press the button next to the down arrow symbol until the + and - symbols are displayed.
Press the button next to the arrow symbols to move to the numeric character to be changed.
Press the button next to + to increase the value or select a parameter; press - to decrease.
Press the save symbol to save the changes (make sure the cursor is on the last numeric character).
If the Home button or Previous Main Menu button is pressed before the save symbol, the changes are not saved.

Controller Configuration (PowerCommand 2100 Control) adjustment

Make sure Main Menu 1 is displayed.
Simultaneously press the Home Menu and Previous Main Menu buttons to view the first Controller Configuration menu.
Press the buttons next to the up and down symbols to navigate between menus.
Press the button next to the + or - symbol to select the desired option.
Press the save symbol to save changes; pressing Home or Previous Main Menu before the save symbol leaves changes unsaved.

Convert Day Tank Controller 240 VAC to 120 VAC adjustment

Remove the two jumpers between terminals TB1-6 and TB1-7.
Connect one jumper between TB1-5 and TB1-6 and the other between TB1-7 and TB1-8.
Move selector switch S103 on the control PCB to the up position for 120V.
If equipped with a transformer, remove jumpers between H2 and H3 and connect one between H1 and H3 and the other between H2 and H4.

Day Tank Controller Conversion 240 VAC to 120 VAC adjustment

Remove the two jumpers between terminals TB1-6 and TB1-7 and connect one between TB1-5 and TB1-6 and the other between TB1-7 and TB1-8.
Move selector switch S103 on the control PCB to the up position for 120V.
On the control transformer, remove the two jumpers between terminals H2 and H3 and connect one between H1 and H3 and the other between H2 and H4.

Dip Adjustment adjustment

Turn the DIP pot clockwise to increase the voltage vs frequency slope for frequencies below the UFRO threshold.
Greater slope gives greater voltage roll off as frequency drops, easing large load pickup but increasing voltage dip.
Turn the pot fully counterclockwise to make the slope the same above and below the threshold frequency.

Dwell Adjustment adjustment

Turn the DWELL pot clockwise to increase dwell time (voltage recovery time when frequency dips below threshold).
Turn the DWELL pot fully counterclockwise to eliminate dwell.
With no dwell, voltage recovery follows engine speed recovery.

Electric Governor Controller Adjustments adjustment

⚠ If adjustment must be made while the unit is running, use extreme caution around hot manifolds and moving parts

Tools: Frequency meter

Move RUN/STOP/REMOTE switch to RUN and operate set at no load.
Confirm DROOP potentiometer adjust is set at zero position.
Set speed by adjusting the SPEED potentiometer to 50 or 60 Hz.
Adjust GAIN potentiometer clockwise until engine starts to hunt, then counterclockwise until speed is stable.
Adjust the 'B' potentiometer the same as GAIN.
Adjust the 'I' potentiometer to decrease overshoot above rated speed.
Apply 1/4 load and adjust the GAIN potentiometer again.
Apply full load to be certain the set will carry it; lengthen actuator linkage if it will not.

Governor Adjustments (Type A Electric Governor) adjustment

Set selector switch S1 to OFF, S2 to appropriate model position.
Set pots initially: Gain 20%, I 20%, D 30%, Droop 0%.
Start set, adjust Speed pot for required frequency (60Hz=1800RPM or 50Hz=1500RPM) at operating temperature.
Disconnect load, turn Gain pot to 100% or until unstable, then back off until stable.
Adjust D and I pots similarly; readjust Speed if necessary.
Push throttle to minimum speed, release and observe overshoot (2-5 Hz acceptable); adjust I pot to reduce overshoot or hunting.

Initial Start Setup adjustment

⚠ Selecting this menu resets all operating parameters to default values; perform only by technically qualified personnel.

Press RESET, MENU and PHASE SELECT simultaneously to invoke the Initial Start Setup menu.
Toggle the Standby/Prime option.
Select the correct generator set model, frequency and kW rating.
Select the correct nominal line-to-line output voltage.
Select DELTA or WYE.
Select SAVE to save changes; MAIN MENU is then displayed.

Mechanical Governor Adjustment adjustment

Tools: Accurate frequency meter

Using an accurate frequency meter, measure frequency under full load.
Turn the speed adjustment screw on the governor to adjust to nominal 50 or 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.

Voltage reconnection

Voltage	Phase	Connection	Leads	Notes
		AVR response jumper	A to C	For generator output 90 kW or less (SX440 and MX321)
		Auxiliary terminal board TB21	K1, K2, P2, P3, P4, S2, S1, A2, A1	A1 and A2 connect a VAR/power factor controller when paralleling with a utility; S1 and S2 connect a droop compensating CT when paralleling with a generator set or utility
		CT1 - U load leads (A phase); CT2 - V load leads (B phase); CT3 - W load leads (C phase)	6 lead gensets: generator output leads routed through CTs; 12 lead gensets: load wires routed through CTs	12-lead sets have dual secondary CTs (3 pins); 6-lead sets have single secondary CTs (2 pins)
		Day tank LO SHUTDOWN engine shutdown connection	TB1-14 to engine block ground; TB1-15 to TB2-16 on the ECM
		Fault relay K8/K9 (Dry Contact Module)	K8=Over Crank, Low Oil Pressure, High Engine Temperature, Low Coolant Level, Low Fuel Level; K9=Low Fuel Level, Rupture Basin	Contact ratings: 40A max carry/break N.O. 12V coil, 30A N.C. 12V coil, 20A N.O./10A N.C. 24V coil
		MX321 PMG-excited jumper positions	2-3, 4-5 and 6-7	These jumpers must be in these positions
		MX321 voltage regulator frequency jumper	3-2 for 50 Hz; 3-1 for 60 Hz
		SX440 voltage regulator frequency jumper	C-50 for 50 Hz; C-60 for 60 Hz
		TB3 (ECM alternative RUN/STOP/REMOTE connection)	TB3-1=REMOTE, TB3-2=RUN, TB3-3=STOP	Provides alternative direct connection to ECM for troubleshooting or customer connection
		Voltage trimmer R21	voltage regulator terminals 1 and 2	There must be a jumper between terminals 1 and 2 when voltage trimmer R21 is not used
	single phase	QSG-Series power distribution panel voltage selector switch S1 position	main output terminals	Rotary switch under lockable cover selects 120/240 VAC single phase
	single phase	Voltage regulator terminal 6	jumpered to terminal 8	When the generator is connected for single-phase output, terminal 6 is not connected to the isolation transformer
	three phase	QSG-Series power distribution panel voltage selector switch S1 position	main output terminals	Rotary switch selects 120/208 VAC three phase
110V - 120V L-N	Single phase, 2-wire	Jumper locations for single phase, 2-wire		PTC Module AC wiring (0300-5382-01, -02)
120	single phase	Day tank fuel pump control power reconnection	move jumpers from TB1-6/TB1-7 to TB1-5/TB1-6 and TB1-7/TB1-8	Move selector switch S103 on the control PCB to the up position for 120 V (factory set for 240 V, S103 down)
190, 200, 208, 220, 230, 240, 380, 416, 440, 460, 600 (L-L)	3 (three phase)	3 or 4 wires		Voltage Configuration submenu; default = 3Ph 208V 4W
190V - 240V L-L	Three phase	Jumper locations for three phase, 190V-240V L-L		Use 0300-5382-01 for 190V-240V L-L, 50/60 Hz
200, 220, 230, 240 (L-L)	1 (single phase)	3 wires		Voltage Configuration submenu (Governor/Regulator Setup)
200V - 240V L-L	Single phase, 3-wire	Jumper locations for single phase, 3-wire		PTC Module AC wiring
24		Day tank fuel pump control logic power (two lead harness, no transformer)	TB1-19 to positive (+) 24 V starter motor solenoid; TB-20 to negative (-)	Provides 24 VDC for the control circuit
240	single phase	Day tank fuel pump control default factory connection	jumpers between terminals TB1-6 and TB1-7	Selector switch S103 on the control PCB in the down position for 240 V
380V - 600V L-L	Three phase	Jumper locations for three phase, 380V-600V L-L		Use 0300-5382-02 for 380V-600V L-L, 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 6BT5.9 family

Part #	Description	Category
982-0200	Air Filter	air_filter
3824469	fuel pump gear puller	fuel_pump
DM-3801372	Gasket Set - 6BT 5.9	gasket
FP-6B59PREM	6B/6BT5.9 In-Frame Kit w/upper gasket set & oil pan gasket	gasket
FP-6B59PREML	6B/6BT5.9 In-Frame Kit w/upper gasket set & oil pan gasket (late)	gasket
FP-IFK6B59PREM	6B/6BT5.9 In-Frame Kit w/upper gasket set & oil pan gasket	gasket
FP-IFK6B59PREML	6B/6BT5.9 In-Frame Kit w/upper gasket set & oil pan gasket (late)	gasket
3822509	injector puller	injector
3823276	injector bore brush	injector
DM-3029551	Fuel Injector - 6BT 5.9	injector
LF3349	Lube, Full-Flow Spin-On	oil_filter
3377259	bosch timing tool (ve)	other_service
960-0627C		other_service
965-0520	Cooling Fan	other_service
DM-3802010	Main Bearing Set Standard - 4BT 3.9, 6BT 5.9, 6CT 8.3	other_service
FP-3356970	6B/6BT5.9 In-Frame Kit (contains FP-3802160 Piston Kit)	other_service
FP-3356971	6B/6BT5.9 In-Frame Kit (contains FP-3802248 Piston Kit)	other_service
TB1-7	B+ OUTPUT	other_service
DM-3805401	Oil Pump - 6BT 5.9	pump
DM-3805403	Water Pump - 4BT 3.9, 6BT 5.9	pump
S103	Selector switch	switch
TB1-6	Control box terminal (TB1-6)	terminal
DM-3015282	Thermostat 180F - 4BT 3.9, 6BT 5.9	thermostat

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

Common questions

What is the oil capacity of the Cummins/Onan 6BT5.9-G6?

The Cummins/Onan 6BT5.9-G6 engine has an oil capacity of 100.0 liters.

What is the displacement of the Cummins/Onan 6BT5.9-G6?

The Cummins/Onan 6BT5.9-G6 has a displacement of 5.88 liters with 6 cylinders.

Which generators use the Cummins/Onan 6BT5.9-G6 engine?

The Cummins/Onan 6BT5.9-G6 powers 3 generator set(s), including Cummins/Onan C110D6, Cummins/Onan C120D5, Cummins/Onan DGDB.

What is a common problem with the Cummins/Onan 6BT5.9-G6 engine?

A commonly reported issue on generators using the Cummins/Onan 6BT5.9-G6 is: Over Current.