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Cummins/Onan 4B3.9-G2 Engine

The Cummins/Onan 4B3.9-G2 is a 3.9 L 4-cylinder naturally aspirated engine rated at 1800 rpm, producing up to 50.7 kW. It powers generator sets from Cummins/Onan, including the C40 D6, C45D5 and DGBB. It holds 10.9 L (2.9 gal) of oil and 16.9 L (4.5 gal) of coolant.

Also known as: Cummins 4B3.9-G2

Part of the Cummins/Onan 4B3.9 engine family — 5 variants share parts & fitment.

3.9 L

Displacement

Cylinders

1800 rpm

Rated speed

50 kW

Gross power

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

Engine specifications

Oil capacity	10.9 L
Coolant capacity	16.9 L
Displacement	3.9 L
Cylinders	4
Aspiration	Naturally aspirated
Rated speed	1800 rpm
Gross power	50 kW

Generator sets powered by this engine

Cummins/Onan C40 D6 Cummins/Onan C45D5 Cummins/Onan DGBB

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

Common problems

Engine cranks but will not start
Cause: Empty fuel tank, fuel leaks, or plugged fuel lines
Fix: Correct as required
Low Battery Voltage — Battery voltage is low 441
Cause: Damaged battery cable connections
Fix: Inspect the battery cable connections for loose connections and/or corrosion, and repair as necessary
Excitation Fault (Loss of AC Sense) — The control has lost voltage sensing or has lost zero cross sensing 2335
Cause: Incorrect configuration
Fix: Make sure that values for the Low of AC Voltage Threshold (85%) and Low of AC Voltage Time Delay (10 seconds) are correct in calibration
Engine Oil Pressure Low (Shutdown) — Engine oil pressure is below the low oil pressure shutdown threshold (35 psig) 415
Cause: Lubricating oil level is low
Fix: Check the oil level. Add or drain oil, if necessary
Over Current 1471
Low Coolant Level 197
Cause: Engine coolant level has fallen below the warning trip point
Fix: If generator is 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.
Engine Is Difficult to Start or Does Not Start
Cause: Battery voltage is low, interrupted, or open
Fix: Check the battery connections, unswitched battery supply circuit, and fuses
Low Coolant Level (Warning or Shutdown) — This fault is used when an optional coolant level sensor is installed. The nature of the fault is an optional customer selection 1317
Cause: Low coolant
Fix: Stop the engine and allow the engine to cool down; Visually inspect and verify that the engine coolant is at the appropriate level; If the coolant level is too low, add coolant per specifications
Engine Noise Is Excessive
Cause: Lubrication issue(s)
Fix: Check the oil level and fill the system to the specified level if lubricating oil level is below specification; check the oil pressure if lubricating oil pressure is below specification; analyze the oil if lubricating oil is thin or diluted
Engine Experiences Low Power, Poor Acceleration, or Poor Response
Cause: Excessive load
Fix: Ensure that the load on the generator set does not exceed the generator set kW rating; revisit the generator set sizing process to ensure that the generator set is correctly sized for the application, especially if new loads have been introduced into the system
Unstable Voltage (With Load)
Cause: Engine governing unstable
Fix: Refer to the engine service manual (if applicable) or E-Controls service manual
Poor Voltage Regulation (With Load)
Cause: Unbalanced load
Fix: Check voltage and load current on all phases; if unbalanced, redistribute the load more evenly across the phases
Poor Engine Transient Response
Cause: Excessive loads
Fix: Make sure that the load on the generator set does not exceed the generator set KW rating; re-visit the generator set sizing process to make sure that the generator set is correctly sized for the application, especially if new loads have been introduced into the system
Low Voltage (With Load)
Cause: Under frequency roll-off protection activated
Fix: Under frequency roll-off protection is activated, indicating excessive load; check that under frequency roll-off set point and slope are correct; load on generator is in excess of rated, ensure that the load on the generator set does not exceed the generator kW rating; revisit the generator set sizing process to ensure that the generator set is correctly sized for the application, especially if new loads have been introduced into the system
Low Fuel (Warning or Shutdown) — This fault is used when an optional low fuel level switch is installed. The nature of the fault is an optional customer selection 1318
Cause: Low fuel level
Fix: Add the manufacturer's prescribed fuel

Compiled from service & troubleshooting documentation across every generator set that uses the Cummins/Onan 4B3.9-G2.

Maintenance schedule

Item	Spec	Capacity	Part #	Interval
Air filter			—
Fuel filter			—
Oil filter	Single spin-on canister, full flow		—	695 hr
Battery	Set mounted starting battery.		—
Belt			—
Coolant		17.3 liters	—
Oil		10.9 liters	—
Spark plug			—

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
Charge air piping	Check	50 hr		Daily or after 8 hours
Coolant level	Check	8 hr		Daily or after 8 hours
Exhaust system	Inspect	8 hr		Visually and audibly inspect the exhaust system daily for leaks per the maintenance schedule; check for corrosion, obstruction, and leaks every time you start the generator set and every eight hours when you run it continuously
Fuel Filter(s)	Drain	8 hr		Drain 1 cup or more of fuel to remove water and sediment. Refer to engine operation and maintenance manual for procedure.
Fuel Tanks (water and sediment)	Drain	8 hr		Drain 1 cup or more of fuel to remove water and sediment.
Fuel level	Check	8 hr		Daily or after 8 hours
General genset inspection	Inspect	8 hr		Daily or after 8 hours. Check for oil, fuel, cooling and exhaust system leaks; check exhaust audibly and visually with set running.
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		Keep oil level near the dipstick high mark without overfilling.
Air cleaner restriction indicator	Check	24 hr		If service indicator shows red, replace air cleaner elements and reset indicator.
Coolant level of radiator(s)	Check	24 hr		Top up with Cummins recommended coolant mix if low.
Engine oil level	Check	24 hr		Top up with recommended oil if low.
Fuel level in fuel tank	Check	24 hr		Refill as required.
Fuel lines and hoses	Check	24 hr		Check for leaks, worn or damaged hoses.
Generator set enclosure	Inspect	24 hr		Walk-around; ensure no inlets/outlets covered.
Operator panel operation	Check	24 hr		Check display; replace component if not functioning.
Air Cleaner	Clean	50 hr		Clean if required. Perform more often in dusty conditions.
Air cleaner (clean if required)	Clean	50 hr		Weekly or after 50 hours; perform more often in dusty conditions
Air intake system for leaks	Inspect	50 hr		Visually inspect; check audibly when running.
Battery charging system	Check	50 hr		Weekly or after 50 hours
Battery connections	Check	50 hr		Verify connections are secure.
Charge alternator	Check	50 hr		Check visually and audibly when running.
Coolant heater	Check	50 hr		Weekly or after 50 hours
Coolant lines and radiator hoses	Check	50 hr		Check for leaks, wear, and cracks.
Cooling fan blades	Inspect	50 hr		Visually inspect through guarding.
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.
Drive belt condition and tension	Check	50 hr		Check for wear or slippage.
Exhaust components and hardware	Check	50 hr		Visually inspect; check audibly when running.
Exhaust condensate trap	Drain	50 hr		Weekly or after 50 hours
Radiator air flow	Inspect	50 hr		Check for blockage, debris, wear or damage.
Water and sediment from fuel tank	Drain	50 hr		Weekly or after 50 hours; drain 1 cup or more of fuel to remove water and sediment
Radiator hoses for wear and cracks	Inspect	100 hr		Monthly or after 100 hours
Starting batteries	Check	100 hr		Monthly or after 100 hours
Battery electrolyte level	Check	200 hr		Check at least every 200 hours of operation
Engine oil and filters	Replace	200 hr		First service — After the initial 50 hour interval and every 200 hours thereafter (footnote 3).
Anti-freeze and DCA Concentration	Check	250 hr	3 mo	Refer to engine operation and maintenance manual.
Crankcase oil and filter	Change	250 hr	12 mo	Refer to Cummins Engine Operation and Maintenance Manual. Standby applications: change every 12 months or 250 hours, whichever comes first.
Drive Belt Tension	Check	250 hr	3 mo	Visually check belt for evidence of wear or slippage. Replace if hard or brittle. Refer to engine operation and maintenance manual.
Fuel Filters	Change	250 hr	3 mo	Refer to engine operation and maintenance manual.
Governor Adjustment	Check	250 hr	3 mo

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	Float switch lift below C-clip stop	1/8	inch (3 mm)
Clearance	Overspeed switch magnet-to-fly arm air gap (minimum)	0.005	inches (0.13 mm)
Gap	MPU sensor tip to ring gear teeth clearance	0.5 - 0.6	mm
Gap	Mechanical overspeed switch air gap between magnet and fly arm (replace switch if less)	0.005	inches (0.13 mm)
Other	AFLEX-H (shake table test datum)	<=3.200	g	AC156, tri-axial, 5% damping SRS
Other	AFLEX-V (shake table test datum)	<=1.333	g	AC156, tri-axial, 5% damping SRS
Other	ARIG-H (shake table test datum)	<=2.400	g	AC156, tri-axial, 5% damping SRS
Other	ARIG-V (shake table test datum)	<=0.533	g	AC156, tri-axial, 5% damping SRS
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 (corrected)	1.260		corrected to 80 °F (27 °C)
Other	Battery recharge threshold specific gravity	1.215
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	Cycle crank crank and rest time	7 to 20	seconds
Other	Cycle crank number of cycles	3, 4, or 5
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	Flywheel teeth (Teeth Pulses Per Revolution)	110		PCC setting
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	Glow plug preheat time	5		glow plug calibration
Other	Glow plug total glow plug time	60		glow plug calibration
Other	Governor droop adjustment range	within 5	percent of nominal frequency (3 Hz for 60Hz sets, 2.5 Hz for 50Hz sets)
Other	Ground snow load limit	30	psf	For indoor (covered) and outdoor (exposed) installation
Other	Horizontal design seismic coefficient (z/h = 0.0)	1.440	g	Certified seismic design level, IBC Importance IP <= 1.5, Soil Classes A-E, Risk Categories I-IV, Design Categories A-F, SDS <= 2.000 g
Other	Low oil pressure / high engine temperature fault time delay	about 10	seconds	following starter disconnect and inhibited during cranking
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	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	SDS (g) at z/h=1 for C10 D6 - C60 D6	2.0	g	Certified SDS, z/h = 1
Other	SDS (g) at z/h=1 for C50 D6C - C125 D6C	2.5	g	Certified SDS, z/h = 1
Other	Setup/calibration menu access code	574
Other	Speed/frequency mismatch threshold	2.0	Hz	PCC setting
Other	Speed/frequency mismatch threshold time	1.5	seconds	PCC setting
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	Trailer brake shoe adjustment back-off	10	clicks
Other	Trailer surge brake actuator stroke length (service brakes if exceeds)	1	inch (25 mm)
Other	Under-frequency roll-off (UFRO) threshold, 50 Hz applications	49	Hz
Other	Under-frequency roll-off (UFRO) threshold, 60 Hz applications	59	Hz
Other	Voltage adjustment range	±5%	%	genset running
Other	ZPA-H (shake table test datum)	<=2.160	g	AC156, tri-axial, 5% damping SRS
Other	ZPA-V (shake table test datum)	<=0.480	g	AC156, tri-axial, 5% damping SRS
Pressure	Engine oil pressure (normal)	30 to 65	psi (207 to 449 kPa)	at normal operating temperature
Pressure	Engine oil pressure range (low oil pressure troubleshooting)	25 to 65	psi (172 to 449 kPa)

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	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 coolant solution (50% pure water and 50% ethylene glycol)
Coolant	50/50 coolant solution (50% water / 50% ethylene glycol)
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.
Engine oil		Refer to Cummins engine Operation and Maintenance Manual for lubricating oil classification		Gensets are shipped with oil added.
Engine oil	15W40		7.9 L (8.35 qt)	Refer to the Engine Operator Manual
Fuel	ASTM number 2D fuel	ASTM 2D
Fuel	Diesel			Do not use zinc coated or copper fuel lines with diesel fuel.
Fuel	Number 2 diesel
Fuel	diesel			Do not use zinc coated or copper fuel lines with diesel fuel.
Grease	Dow Corning silicone heat sink compound type 340 or similar			Apply to base of replacement diode only
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. Grounding the engine idle input inhibits generator build-up and governs the engine at 800 RPM; control lowers oil pressure warning and shutdown trip points accordingly.	Warning	None required; removing ground returns the genset to normal speed and voltage.
102	EMERGENCY STOP	Indicates local or remote Emergency Stop.	Shutdown	Pull the button out (turn clockwise to allow it to pop out); move Run/Off/Auto switch to Off; press the Reset switch; select Run or Auto as required. Reset only at the PCC front panel.
121	SPEED SIGNAL LOST	Mag pickup speed indication is not being sensed.	Shutdown	Restart and check RPM on digital display; inspect MPU wires/connector pins; check for 3.5 to 15 VAC at MPU while cranking.
135	OIL PRESSURE SENSOR H	Engine oil pressure sender signal is shorted 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	Engine oil pressure sender signal is shorted low.	Warning	Check sender/connectors/wires; check for shorts/open circuits at P7-13, 17, 21.
143	PRE-LOW OIL PRES	Engine oil pressure dropped to an unacceptable level.	Warning	Check oil level, lines and filters; replenish if low; if powering critical loads wait until next shutdown period and follow code 415.
144	COOL 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).
145	COOL SENSOR LOW	Engine coolant temperature signal is shorted low.	Warning	Check sender/connectors/wires; check for shorts at P7-30 and P7-34.
146	PRE-HIGH COOL TMP	Engine has begun to overheat (coolant temperature risen to an unacceptable level).	Warning	Reduce load; check air inlets/outlets and remove obstructions to airflow; if engine can be stopped follow code 151.
151	HIGH COOLANT TEMP	Engine has overheated (coolant temperature 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	Allow engine to cool; check coolant level and replenish; look for leaks; reset control and restart.
200	LOW OIL PRESSURE	Indicates engine oil pressure has dropped to an unacceptable level.	Warning	If powering critical loads and cannot be shut down, wait until next shutdown period then follow the 201-SHUTDOWN procedure. Check oil pressure via the Oil Pressure menu prior to clearing the fault.
201	LOW OIL PRESSURE	Indicates engine oil pressure has dropped below the shutdown trip point.	Shutdown	Check oil level, lines and filters; if oil system is OK but oil level is low, replenish; reset control and restart. Oil pressure limits are listed in Table 4-3.
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.
210	LOW COOLANT TEMP	Warning occurs when engine coolant temperature is 70 deg F (21 deg C) or lower while set is not operating.	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 engine coolant temperature is getting close to the recommended maximum (215 deg F/102 deg C standby or 207 deg F/97 deg C prime).	Warning	Reduce load if possible; check air inlets and outlets and remove obstructions to airflow; if engine can be stopped follow the 212-SHUTDOWN procedure.
212	HIGH COOLANT TEMP	Indicates engine has overheated (coolant above 223 deg F/106 deg C standby or 215 deg F/102 deg C prime).	Shutdown	Allow engine to cool; check for obstructions to cooling airflow, check fan belt, check coolant mixture, check blower fan and circulation pumps; reset control and restart after correcting problem.
213	COOLANT SENDER	Indicates that the 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	Allow engine to cool; check coolant level in radiator and recovery bottle and replenish if low; check for possible coolant leakage points.
215	LOW COOLANT LVL	Indicates engine coolant level has fallen below the shutdown trip point.	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	Indicates 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	Indicates possible fault with control or starting system.	Shutdown	Check fuse F3 on the Engine Interface board; clean battery cable connections; recharge or replace battery.
222	OVERCRANK	Indicates possible fuel system problem.	Shutdown	Check for empty fuel tank, fuel leaks, or plugged fuel lines; check for dirty fuel filter and replace; check for dirty or plugged air filter and replace; reset control and restart.
223	OVERSPEED	Indicates engine has exceeded normal operating speed (115% +/-1% of nominal).	Shutdown	Inspect mechanical fuel linkage; check EFC for binding/damage; monitor PCC duty cycle 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	Check battery charger fuse and recharge or replace battery; clean and tighten battery cable connections; check engine DC alternator; check battery charge voltage float level.
231	HIGH DC VOLTAGE	Indicates battery voltage exceeds 32 VDC.	Warning	Check voltage float level on battery charger (lower float level); check engine DC alternator and replace if normal charging voltage is not obtained.
232	WEAK BATTERY	Indicates battery voltage drops below 60% of nominal for two seconds during starting.	Warning	Discharged or defective battery; see warning message 230, LOW DC VOLTAGE.
234	OVERSPEED	Engine has exceeded normal operating speed.	Shutdown	Clear fault and restart genset; check fault threshold; monitor RPM; check electronic governor actuator.
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.
240	LOW FUEL-DAY	Indicates day tank fuel supply is running low.	Warning	Check fuel supply and replenish as required.
241	LOW FUEL	Indicates fuel supply is running low.	Warning	Check fuel supply and replenish as required.
250	EEPROM ERROR	Indicates PCC memory error - data corruption of critical operating parameters.	Shutdown	Perform initial start setup; turn Run/Off/Auto to Off and reset; if the same EEPROM ERROR message occurs, replace the digital board (A32).
251	EEPROM ERROR	Indicates PCC memory error - data corruption of noncritical operating parameters.	Warning	Perform adjustment procedures and save; if the same EEPROM ERROR message occurs, replace the digital board (A32).
252	EEPROM ERROR	Indicates PCC memory error - data corruption of noncritical operating parameters.	Warning	Verify values/choices selected and repeat the save operation; if the same EEPROM ERROR message occurs, replace the digital board (A32).
260	CUSTOMER FAULT 1	Customer defined input closed to ground; message is editable.		Isolate the source of the false signal; check A34 LED corresponding to the fault input.
261	GROUND FAULT	Customer defined input closed to ground (default message); message is editable.		Isolate the source of the false signal; check A34 LED corresponding to the fault input.
262	RUPTURE BASIN (DAY TANK)	Customer defined input closed to ground; message is editable.		Isolate the source of the false signal; check A34 LED corresponding to the fault input.
263	HIGH GEN TEMP	Customer defined input closed to ground (default message); message is editable.		Isolate the source of the false signal; check A34 LED corresponding to the fault input.
270	PHASE ROTATION	The phase relationship between the generator set and the system bus is not matched.	Shutdown	Using a phase rotation checker, verify that the generator set phase rotation matches the system bus; verify control wiring to the bus PT module is properly connected.
272	FIRST START	The PowerCommand control is not receiving a proper signal from the system master first start sensor.	Warning	Control reverts to fallback mode; verify the Master First Start Sensor is functioning and that the voltage pulse is present at the PowerCommand control (terminal TB1-50); check interconnection wiring.
301	HIGH AC VOLTAGE	Indicates that one or more phase voltages has exceeded 130% of nominal, or exceeded 110% of nominal for 10 seconds.	Shutdown	Isolate the regulator module (A37), engine interface board (A31), digital board (A32), PMG/field wiring or PT/CT sensing path per troubleshooting table 4-29.
303	LOW AC VOLTAGE	Indicates that one or more phase voltages has dropped below 85% of nominal for 10 seconds.	Shutdown	Check PMG or field wiring, rotating rectifier diodes, overload, loose connectors, and voltage sensing circuitry per troubleshooting table 4-30.
313	UNDER FREQUENCY	Indicates that engine speed has dropped below 90% of nominal for 10 seconds. (Five seconds before shutdown, a Load Dump signal is initiated.)	Shutdown	Check fuel supply, intake air supply and load; check Initial Setup (set size).
320	OVERCURRENT	Indicates that generator output current has exceeded 110% of rated for 60 seconds.	Warning	Check load and load lead connections.
321	OVERCURRENT	Indicates that generator output current has exceeded 110% of rated, and a PCC time/current calculation has initiated an overcurrent shutdown.	Shutdown	Check load and load lead connections.
322	SHORT CIRCUIT	Indicates that generator output current has exceeded 175% of rated.	Shutdown	Check load and load lead connections.
330	OVERLOAD	Indicates that three-phase power output exceeds 105% of standby (or 115% of prime) rating.	Warning	Check load and load lead connections.
335	REVERSE POWER	Indicates that power is flowing into the generator set rather than out from the unit.	Shutdown	Verify connection of generator set CT's; verify proper connection of load sharing lines; verify correct frequency and voltage on all sets.
337	LOSS OF EXCITATION	Indicates that the alternator excitation system is improperly adjusted or has failed.	Shutdown	Check output voltage with calibrated meter and adjust; check load sharing lines; see Section 6 Servicing the Generator.
359	FAIL TO START	Engine cranks but fails to start (possible fuel system problem).	Shutdown	Check for empty fuel tank, fuel leaks, or plugged fuel lines; replace dirty fuel filter; replace dirty air filter; reset control and restart.
415	LOW OIL PRESSURE	Engine oil pressure has dropped below the shutdown trip point.	Shutdown	Check oil level, lines and filters; replenish if low; reset control and restart.
421	OIL TEMP	Engine has begun to overheat (oil temperature above unacceptable level) (Optional).	Warning	Reduce load; check air inlets/outlets; if engine can be stopped follow code 151 and check engine oil level.
441	LOW BAT VOLTAGE	Battery voltage supply to the control approaching a low level.	Warning	Check battery charger fuse; recharge or replace battery; clean and tighten cable connections; check engine DC alternator.
442	HIGH BAT VOLTAGE	Battery voltage supply approaching a high level at which control damage can occur.	Warning	Check float level on battery charger; check battery wiring/calibration.
1122	Rated/Idle Trans		Info
1123	SHUTDOWN AFTER BS	A shutdown fault occurred while Battle Short was enabled and transitioned from enabled to disabled.	Shutdown	Review Fault History and perform corrective action.
1124	DELAYED SHUTDOWN	A shutdown fault became active while the Delayed Shutdown feature was enabled.	Warning	Review Fault History and perform corrective action.
1131	BATTLE SHORT ACTIVE	Control is in Battle Short mode (bypasses several critical fault shutdowns).	Warning	None; used for genset operation during emergencies.
1311	Customer Input #1	Configurable customer input 1 fault.	Warning	Check TB1-12; check external wiring; verify fault function settings.
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	Configurable customer input 2 fault.	Warning	Check TB1-14; check external wiring; verify fault function settings.
1317	Low Coolant Level	Optional coolant level sensor indicates low coolant level.	Warning	Add coolant; check coolant level sensor connections and operation; verify calibration.
1318	Low Fuel	Optional low fuel level switch indicates low fuel.	Warning	Add fuel; verify switch operation; check wiring; verify settings.
1334	CRIT SCALER OR	Incorrect feature or calibration was entered into control.	Shutdown	Reload correct feature/calibration file.
1335	NONCRIT SCALER OR	Incorrect feature or calibration was entered into control.	Warning	Reload correct feature/calibration file.
1337	No Message		Info
1416	FAIL TO SHUTDOWN	Genset continues to run after receiving shutdown command (Battle Short feature enabled).	Warning	Check Battle Short feature setting.
1417	POWER DOWN ERROR	Controller cannot power down because of an unknown condition.	Warning	Check for possible battery drain.
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	Engine coolant heater is not operating or not circulating coolant (coolant <=70 F [21 C]).	Warning	Check coolant heater power/fuse/cord; check coolant level; check heater element (10 to 60 ohms); check sensor.
1438	FAIL TO CRANK	Engine failed to crank after the PCC received a start signal.	Shutdown	Test for B+ at the starter; check fuse F3 (2 Amps); check K4 start pilot relay and starter circuitry; refer to code 121.
1442	WEAK BATTERY	During cranking battery voltage at or below weak battery trip point.	Warning	Recharge or replace battery; check electrolyte level and connections; check harness.
1443	BATTERY FAILED	Dead battery - engine will not start.	Shutdown	See code 1438 instructions.
1444	KW OVERLOAD	Generator output power exceeded 105% of genset rating (3 sec at 110% of rated).	Warning	Check load and load lead connections; check CTs and CT connections.
1445	SHORT CIRCUIT	Generator output current exceeded 175% of rated.	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.

Showing the first 80 of 145 codes.

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 Values/Parameters adjustment

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

Press button next to symbol in display until + and − symbols are displayed.
Press button next to arrow symbols to move to numeric character to change.
Press button next to + symbol to increase value or select parameter.
Press button next to − symbol to decrease value or select parameter.
After adjusting values/selecting parameters, press symbol to save changes.

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.

Disabling the AMF Feature adjustment

⚠ Must be performed by a qualified technician.

Tools: InPower service tool

Connect to the PCC 1.1 or PCC 2.3 via InPower.
Navigate to Adjustments->Features->Automatic Transfer Switch folder.
Select the Auto Mains Failure Enable parameter.
Double-click on Enabled in the Value field.
Select Disabled from the pop-up choices.
Select Device->Save Adjustments from the top menu bar.
Click Save on the confirmation pop-up.
Disconnect InPower from the PCC1302 after confirmation.

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.

Fuel Injection Pump Speed Lever Adjustment adjustment

Make sure the generator set is off and the battery is disconnected.
If replacing pump or engine, discard speed adjust screw and tamper proof wire and seal.
Replace the low idle screw; reuse throttle screw nut and acorn nut.
Pull throttle lever back and screw new low idle screw until it contacts boss.
Continue tightening until throttle lever is locked in place.
Tighten the throttle lock nut.
Install tamper proof wire and seal.
Set the throttle lever as shown and lock it using seal wire.

Fuel Pump Control: Convert 120 VAC to 240 VAC adjustment

Remove jumpers between TB1-5/TB1-6 and TB1-7/TB1-8; connect two jumpers between TB1-6 and TB1-7.
Move selector switch S103 on control PCB to down position for 240 VAC.
If equipped with a transformer, remove jumpers between H1/H3 and H2/H4 and connect two jumpers between H2 and H3.
Attach a tag to the control box indicating the supply voltage.

Fuel Pump Control: Convert 240 VAC to 120 VAC adjustment

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

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.

Operating PowerCommand in Droop Mode adjustment

Set the no load speed and voltage at the desired level (bus must be de-energized or disconnect Bus PT module).
Apply 100% load and adjust KW load sharing gain for desired full load frequency; adjust KVAR load sharing gain for desired full load voltage.
Repeat the process for other generator sets in the system.
Test the system with all available load and verify approximately equal load sharing at no load and maximum load.

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 4B3.9 family

Part #	Description	Category
140-2641	Tube, Air Cleaner	Air filter
140-3218	Cleaner Assembly, Air (Includes	Air filter
982-0200	Air Filter	Air filter
300-3606	Voltage Regulator Installation (PMG-Excited Generators), Rev. P	Avr
300-3607	Voltage Regulator Installation (Self-Excited Generators), Rev. G	Avr
191-1965	Tensioner, Belt	Belt
191-2149-02	Tensioner, Belt	Belt
505-0055	Element, Fuel	Fuel filter
140-3255	*Hose, Breather	Hose
502-0827	Fitting, Hose – Barbed (1/2” ID Pipe to 3/4” ID Hose)	Hose
502-1317	Fitting, Hose Barbed	Hose
503-1707	*Hose, Intake (2–1/2” ID)	Hose
102-1490-00	Kit, Oil Sampler (Includes	Oil filter
102-1490-01	Valve, Oil Sampler	Oil filter
154-3078	Manifold, Oil Pressure	Oil filter
501-0575	Hose Assembly, Oil (3/4–16	Oil filter
501-0685	Line, Oil	Oil filter
504-0176	Valve, Oil Drain	Oil filter
140-1260	Fitting, Safety Filter	Service part / kit
201-3434-01	Diode, Positive (Forward) Includes Lead	Service part / kit
201-3434-02	Diode, Negative (Reverse) Includes Lead	Service part / kit
220-4289-31	Main stator assembly (broad range generators)	Service part / kit
220-4289-32	Main stator assembly (broad range generators)	Service part / kit
220-4289-33	Main stator assembly (broad range generators)	Service part / kit
220-4289-34	Main stator assembly (broad range generators)	Service part / kit
220-4289-35	Main stator assembly (broad range generators)	Service part / kit
220-4298-31	Main stator assembly	Service part / kit
220-4298-32	Main stator assembly	Service part / kit
220-4298-33	Main stator assembly	Service part / kit
220-4298-34	Main stator assembly	Service part / kit
220-4298-35	Main stator assembly	Service part / kit
220-4298-36	Main stator assembly	Service part / kit
300-4111	Auxiliary Relay Board (ARB), Rev. E	Service part / kit
319-0969	QS-Series Power Distribution Panel Wiring, Rev. G	Service part / kit
3905125	Solenoid, Fuel Shutoff – MCGGA, 24 Volt, Negative Ground Electrical System (Cummins part number)	Service part / kit
3921930	Solenoid, Fuel Shutoff – 12 Volt (Cummins part number)	Service part / kit
3921976	Solenoid, Fuel Shutoff – 24 Volt (Cummins part number)	Service part / kit
502-0153	Plug, Hex Head	Service part / kit
612-6487	7-Light DC Control Wiring Diagram, Sh 1 and 2 of 2, Rev. V	Service part / kit
612-6488	12-Light DC Control Wiring Diagram, Sh 1 and 2 of 2, Rev. W	Service part / kit
612-6489	AC Control Wiring Diagram (Without Meters), Rev. S, modified 6/2001	Service part / kit
612-6490	AC Control Wiring Diagram (With Meters), Rev. ZB, modified 1/2002	Service part / kit
625-2164	Generator Reconnection Diagrams, Sh 1 and 2 of 2, Rev. K	Service part / kit
625-2256	QS-Series Generator Connections When The Voltage Selector Switch Is Provided, Rev. B	Service part / kit
965-0520	Cooling Fan	Service part / kit
625-2141	Day Tank Pump Control Wiring, Rev. P	Pump
509-0266-01	Ring, O	Seal
150-2201	Sensor, Speed – Magnetic	Sensor
517-0291	Plug, Taper	Spark plug

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 4B3.9-G2?

The Cummins/Onan 4B3.9-G2 engine has an oil capacity of 10.9 liters.

What is the displacement of the Cummins/Onan 4B3.9-G2?

The Cummins/Onan 4B3.9-G2 has a displacement of 3.9 liters with 4 cylinders.

Which generators use the Cummins/Onan 4B3.9-G2 engine?

The Cummins/Onan 4B3.9-G2 powers 3 generator set(s), including Cummins/Onan C40 D6, Cummins/Onan C45D5, Cummins/Onan DGBB.

What is a common problem with the Cummins/Onan 4B3.9-G2 engine?

A commonly reported issue on generators using the Cummins/Onan 4B3.9-G2 is: Engine cranks but will not start. Cause: Empty fuel tank, fuel leaks, or plugged fuel lines. Fix: Correct as required.