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Cummins/Onan 4BT3.9-G4 Engine

Name: Cummins/Onan 4BT3.9-G4 Engine
Brand: Cummins/Onan

The Cummins/Onan 4BT3.9-G4 is a 3.9 L 4-cylinder turbocharged engine rated at 1800 rpm, producing up to 73.9 kW. It powers generator sets from Cummins/Onan, including the 40DGCA, 50 DGCA, 50DGCB and 60 DGCB. It holds 11.5 L (3.0 gal) of oil and 16.9 L (4.5 gal) of coolant.

Also known as: Cummins 4BT3.9-G4

Part of the Cummins/Onan 4BT3.9 engine family — 5 variants share parts & fitment.

3.9 L

Displacement

Cylinders

1800 rpm

Rated speed

73 kW

Gross power

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

Engine specifications

Oil capacity	11.5 L
Coolant capacity	16.9 L
Displacement	3.9 L
Cylinders	4
Aspiration	Turbocharged
Rated speed	1800 rpm
Gross power	73 kW

Generator sets powered by this engine

Cummins/Onan 40DGCA Cummins/Onan 50 DGCACummins/Onan 50DGCBCummins/Onan 60 DGCB Cummins/Onan C50 D6 Cummins/Onan C65D6 Cummins/Onan C70 Cummins/Onan C70D5 Cummins/Onan DGCB

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

Common problems

Over Current 1471
Low Coolant Level 197
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: 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.
OVERCRANK lamp lights and engine stops cranking.
Cause: Indicates possible fuel system problem.
Fix: 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.
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.
Cause: Indicates diesel fuel supply is running low.
Fix: Check fuel supply and replenish as required.
Engine runs and then shuts down, OVERSPEED lamp lights.
Cause: Indicates engine has exceeded normal operating speed.
Fix: Contact an authorized service center for service.
Low Battery Voltage 441
High Battery Voltage 442
Weak Battery 1442
Under Frequency 1448
Too Long in Idle 2342
The engine does not start
Cause: The starter will disengage after a specified period of time and the control will indicate an overcrank shutdown.
Fix: Place the O/Manual/Auto switch in the O position and press the Fault Acknowledge/Reset button. Before attempting to restart, wait two minutes for the starter motor to cool and then repeat the starting procedure. If the engine does not run after a second attempt, refer to the Troubleshooting section.
Status Indicators are not functioning properly.
Fix: Check the status indicators for any visible damage or loose connections. If the issue persists, refer to the Fault Code Table for further troubleshooting.

Compiled from service & troubleshooting documentation across every generator set that uses the Cummins/Onan 4BT3.9-G4.

Maintenance schedule

Item	Spec	Capacity	Part #	Interval
Air filter	Normal duty air filter		0140-3765		Amazon eBay
Fuel filter	Single spin-on canister, full flow		—	500 hr
Oil filter	Single spin-on canister, full flow		—	500 hr
Battery	Battery capacity (1x) 75 A/h		—
Belt			328876800		eBay
Coolant	Coolant capacity (only engine)	7.2 l	—
Oil	104oF (40oC) ambient radiator	11.5 L	—	1000 hr
Spark plug	Not applicable		—	1000 hr

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

Service intervals

Item	Action	Hours	Months	Notes
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.
Crankcase oil	Change	50 hr		First service — Drain and replace the crankcase oil after the first 50 hours of operation on new generator sets (break-in)
Drive belt condition and tension	Check	50 hr		Check for wear or slippage.
Engine oil and filter	Change	50 hr		First service — Drain and replace crankcase oil after first 50 hours on new generator sets
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.

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	Automatic stop delay after normal power source returns	about 15 minutes	minutes
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 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	Coolant level below radiator cap opening	2	inches
Other	Coolant level below radiator cap opening	about two inches (50 mm)	mm	cold engine
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	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	Exercise period	at least once a week for a minimum of 30 minutes with load	minutes
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	Power rating reference conditions	altitude 300 feet (92 m), ambient temperature 81 F (27 C)
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)

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		Refer to Cummins engine Operation and Maintenance Manual for coolant recommendations/specifications			Balanced coolant mixture of water, antifreeze and coolant additives.
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.
Coolant	Water/antifreeze mixture				Permanent type antifreeze mixed per supplier for lowest expected ambient; do not use anti-leak additives
Coolant	water/antifreeze mixture			21.0 litres	Capacity with standard radiator 5.5 gallons (21 litres) for 37 DGBA, 35 DGBB, 40 DGBC, 50 DGCA, 60 DGCB; 6.5 gallons (25 litres) for 80 DGDA, 100 DGDB. Do not use antifreeze with anti-leak additives.
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
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	SAE 5W synthetic	API class CC/CD; sulphated ash content does not exceed 1.85 percent; 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 -23°C		For ambient temperature consistently below -10 F (-23 C) with no provision to keep engine warm; do not use petroleum base 5W grade oil
Engine oil	SAE 10W30 / SAE 15W40 / SAE 20W40 (spec table)		-25°C to 35°C	11.0 litres	Specifications table: Oil Capacity with Filters 11.5 quarts (11 litres) for 37 DGBA, 35 DGBB, 40 DGBC, 50 DGCA, 60 DGCB; 17.3 quarts (16 litres) for 80 DGDA, 100 DGDB. Oil type -13 F to 95 F (-25 C to 35 C) SAE 10W30; 14 F (-10 C) and above SAE 15W40; 32 F (0 C) and above SAE 20W40
Engine oil	10W-30	API CC/CD	-23°C to -10°C		-10 F (-23 C) to 14 F (-10 C)
Engine oil	SAE 10W-30	API Class CC/CD (max sulphated ash 1.85 percent)	-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	SAE 15W-40	API Class CC/CD (max sulphated ash 1.85 percent)	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
Engine oil	SAE 20W-40	API Class CC/CD (max sulphated ash 1.85 percent)	above 0°C		32 F (0 C) and above
Fuel	ASTM No. 2 Diesel	ASTM No. 2			Cummins engines on DG series sets normally use ASTM No. 2 Diesel; will operate on alternate diesel fuels within engine manual specifications. Never use galvanized or copper fuel lines, fittings or tanks.
Fuel	ASTM number 2D fuel	ASTM 2D
Fuel	Diesel				Do not use zinc coated or copper fuel lines with diesel fuel.
Fuel	No. 2 diesel				No. 1 fuel or similar acceptable; consult engine manufacturer for non-standard fuel
Fuel	No. 2 diesel fuel				Engine will also operate on No. 1 fuel or other similar fuels; consult engine manufacturer for specific requirements
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; 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		Info
1123	Shutdown After Battle Short	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 Sh Active	Control is in Battle Short mode (bypasses several critical fault shutdowns).	Warning	None; used for genset operation during emergencies.
121	Speed Signal Lost	No engine speed signal detected from crankshaft speed or camshaft position.	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	Configurable customer input 1 fault.	Warning	Optional customer selection (e.g., Low Fuel Day Tank, Water In Fuel, Ground Fault, Low Starting Hydraulic Pressure, Low Starting Air Pressure). Programmable: enable/disable, status/warning/shutdown, active closed or open, and display name.
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	Optional customer selection; programmable (enable/disable, status/warning/shutdown, active open/closed, display name). Default #2 thru #4 - Warning.
1317	Low Coolant Level	Optional coolant level sensor indicates low coolant level.	Warning	Optional customer selection; programmable (default #3 - Low Fuel).
1318	Low Fuel	Optional low fuel level switch indicates low fuel.	Warning	Optional customer selection; programmable (default #4 - Rupture Basin Fault).
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	Incorrect feature or calibration was entered into control.	Warning	Reload correct feature/calibration file.
1337	No Message		Info
135	Oil Pressure Sensor OOR - High	Engine oil pressure sensor signal out of range - shorted high.	Warning	Inspect sensor connections; check supply 4.75-5.25 VDC and signal voltage.
141	Oil Pressure Sensor OOR - Low	Engine oil pressure sensor signal out of range - shorted low.	Warning	Inspect sensor connections; check supply and signal voltage.
1416	Fail To Shutdown	Genset continues to run after receiving shutdown command (Battle Short feature enabled).	Warning	Check Battle Short feature setting.
1417	Powr Down Error	The PCC has failed to go to sleep.	Warning	Verify calibration; cycle B+ power; replace baseboard if fault persists.
143	Pre-Low Oil Pres	Engine oil pressure dropped to an unacceptable level.	Warning	Indicates engine oil pressure has dropped below the warning trip point. If generator is powering critical loads and cannot be shut down, wait until next shutdown period and then follow code 415 procedure.
1433	Local E-Stop	State of the Local Emergency Stop has been changed.	Shutdown	Reset local E-Stop; check E-Stop switch and wiring.
1434	Remote E-Stop	State of the Remote Emergency Stop has been changed.	Shutdown	See code 1433 to reset.
1435	Low Coolant Temperature	Engine coolant temperature below low coolant temperature warning threshold (70 F / 21 C).	Warning	Verify LCT threshold; check coolant heater operation; check ambient temperature.
1438	Fail to Crank	Engine failed to crank after the generator control 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.
144	Engine Coolant Temperature OOR Low	Engine coolant temperature signal out of range - shorted low.	Warning	Inspect sensor connections; check sensor resistance; verify calibration.
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.	Warning	Check threshold, PCC AVR circuit, generator output connections, PMG, EBS.
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	Underfrequency	Frequency dropped below underfrequency threshold (6 Hz) for 10 seconds.	Shutdown	Check overrides, threshold, overload, engine governor.
1449	Overfrequency	Frequency went above overfrequency threshold (6 Hz) for 10 seconds.	Warning	Verify overfrequency threshold and time delay; check engine governor.
145	Engine Coolant Temperature OOR High	Engine coolant temperature signal out of range - shorted high.	Warning	Inspect sensor connections; check sensor resistance; verify calibration.
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	Improper CT phasing.	Shutdown	Check wiring to voltage sense circuit; refer to CT Installation in Section 6.
146	Pre-High Coolant Temp	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.
1461	Loss Of Field	Loss of field (electric) due to reverse kVAR.	Shutdown	Check field circuit.
1466	Modem Failure	Control cannot communicate with the modem.	Warning	Check for open, short circuit to ground, and loose connections to the modem.
1468	Network Error	Momentary loss of communication from the LonWorks Network.	Warning	Refer to the LonWorks Network publications.
1469	Speed/Hz Mismatch	Perceived engine speed and generator set output frequency do not match.	Shutdown	Check flywheel teeth (110), MPU signal, thresholds (2.0 Hz, 1.5 s), gain (30 RPM/Hz).
1471	Over Current	Generator output current exceeded warning limit threshold (110% for 60 seconds).	Warning	Check load and load lead connections.
1472	Over Current	Generator output current exceeded shutdown set limit (150% for 10 seconds).	Shutdown	Check load and load lead connections (fault may not reset for several minutes).
151	High Coolant Temp	Engine has overheated (coolant temperature above the shutdown trip point).	Shutdown	Engine has overheated. Allow engine to cool completely, then: check coolant level and replenish and repair leaks; check for obstructions to cooling airflow; check fan belt and repair or tighten; check blower fan and circulation pumps on remote radiator installations; reset control and restart.
1853	Annunciator Input 1 Fault	Customer fault 1 (input 1, LED 1) on the universal annunciator is active.	Warning	Check condition and wiring at TB1-1; verify configuration; replace annunciator if faulty.
1854	Annunciator Input 2 Fault	Customer fault 2 (input 2, LED 2) on the universal annunciator is active.	Warning	Check condition and wiring at TB1-2; verify configuration; replace annunciator if faulty.
1855	Annunciator Input 3 Fault	Customer fault 3 (input 3, LED 3) on the universal annunciator is active.	Warning	Check condition and wiring at TB1-3; verify configuration; replace annunciator if faulty.
1944	Annunciator Configuration Error	More than one network device configured to activate one annunciator output relay.	Warning	Check network configuration and devices for duplicate use of the same relay output.
197	Low Coolant Level	Engine coolant level has fallen below the warning trip point.	Warning	Indicates engine coolant level has fallen below warning trip point. 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.
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	Check coolant heater power supply, fuse or disconnected heater cord; check for low coolant level and replenish; check for an open heater element by checking current draw of heater.
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	Indicates engine has overheated (coolant temperature above the shutdown trip point: 223°F (106°C) standby or 215°F (102°C) prime).	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 bottle; check coolant bottle hose or radiator cap; reset control and restart.
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; inspect/adjust MPU.
221	FAIL TO CRANK	Possible fault with control or starting system; engine will not crank.	Shutdown	Check fuse F3 on the Engine Interface board; check for poor battery cable connections; recharge or replace a discharged or defective 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.
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.
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 AC Sense)	Loss of all three voltage sense leads or failure in excitation circuit.	Shutdown	Check field wiring (X1 and X2) for shorts or opens.
2336	Memory Error	Control memory error; data corruption of critical operating parameters.	Shutdown	Try reloading calibration file.
2337	Pwr Tran Disabled	PTC module available but PTC feature not enabled.	Warning	Use InPower to enable PTC feature; cycle power off for 5 seconds then repower.
2338	Pwr Tran Failure	PTC module trim enabled but control could not communicate with PTC module.	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 (sleep) function enabled but PTC module or network board is active.	Warning	None required.
234	Overspeed	Engine speed signals indicate engine speed greater than shutdown threshold.	Shutdown	Clear fault and restart genset; check fault threshold; monitor RPM; check electronic governor actuator.
2341	High Control Temp	Control temperature above normal (158 F [70 C]) for time greater than set time.	Warning	Check genset room air flow.
2342	Too Long In Idle (10 min.)	Genset has been in Idle mode too long.	Warning	Indicates genset has been in Idle mode too long (10 minutes maximum).
235	Low Coolant Level	Engine coolant level has fallen below the shutdown trip point.	Shutdown	Coolant level has fallen below the shutdown trip point. Allow engine to cool completely, then check coolant level and replenish, look for possible coolant leakage points and repair; 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 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.

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.

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.

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.

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.

Over / Under Voltage Module Recalibration adjustment

Remove the two screws securing the top to the case and withdraw the top assembly.
Adjust the UNDER setpoint SET pot to 75 percent.
Apply single-phase, 60 Hertz, 104.25 VAC across terminals L and N.
Adjust pot R25 on the PC board until the relay trips (de-energizes).
Adjust the OVER setpoint SET pot to 125 percent.
Apply single-phase, 60 Hertz, 173.75 VAC across terminals L and N.
Adjust pot R26 on the PC board until the relay trips (energizes).
Repeat until no adjustments are necessary, then reassemble the module.

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 4BT3.9 family

Part #	Description	Category
982-0200	Air Filter	air_filter
AN500T0083	ALTERNATOR	alternator
328876800	Belt, V-Grooved	belt
3824469	fuel pump gear puller	fuel_pump
DM-3801371	Gasket Set - 4BT 3.9	gasket
FP-4B39PREM	4B/4BT3.9 In-Frame Kit w/upper gasket set & oil pan gasket	gasket
FP-4B39PREML	4B/4BT3.9 In-Frame Kit w/upper gasket set & oil pan gasket (late)	gasket
FP-IFK4B39PREM	4B/4BT3.9 In-Frame Kit w/upper gasket set & oil pan gasket	gasket
FP-IFK4B39PREML	4B/4BT3.9 In-Frame Kit w/upper gasket set & oil pan gasket (late)	gasket
DM-3805455	Oil Cooler Hose - 4BT 3.9	hose
3822509	injector puller	injector
3823276	injector bore brush	injector
DM-3029550	Fuel Injector - 4BT 3.9	injector
0332-3925-02	Jumper-Terminal	jumper_terminal
0332-3943-02	Jumper-Terminal	jumper_terminal
300-2810	Board - Engine Monitor (All) (Includes Fuses)	other_service
305-0823	# Model MX321	other_service
3377259	bosch timing tool (ve)	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
DM-3004242	Fuel Transfer Pump - 4BT 3.9	pump
DM-3805403	Water Pump - 4BT 3.9, 6BT 5.9	pump
DM-3807788	Oil Pump - 4BT 3.9	pump
0307-3047	Relay (24V)	relay_24v
0249-0814	Relay 2P Base	relay_2p_base
AN500T0013	STARTER MOTOR	starter
0332-3923-02	Terminal Block	terminal_block
0332-4036-02	Terminal Block (Earth)	terminal_block
0332-3927-02	Terminal Block End Plate	terminal_block_end_plate
0332-3926	Terminal Block End Stop	terminal_block_end_stop
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 4BT3.9-G4?

The Cummins/Onan 4BT3.9-G4 engine has an oil capacity of 11.5 liters.

What is the displacement of the Cummins/Onan 4BT3.9-G4?

The Cummins/Onan 4BT3.9-G4 has a displacement of 3.9 liters with 4 cylinders.

Which generators use the Cummins/Onan 4BT3.9-G4 engine?

The Cummins/Onan 4BT3.9-G4 powers 9 generator set(s), including Cummins/Onan 40DGCA, Cummins/Onan 50 DGCA, Cummins/Onan 50DGCB, Cummins/Onan 60 DGCB, Cummins/Onan C50 D6.

How often should you change the oil in the Cummins/Onan 4BT3.9-G4?

The Cummins/Onan 4BT3.9-G4 oil change interval is every 1000 hours.

What is a common problem with the Cummins/Onan 4BT3.9-G4 engine?

A commonly reported issue on generators using the Cummins/Onan 4BT3.9-G4 is: Over Current.