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Cummins/Onan 4BTA3.9-G3 Engine

Name: Cummins/Onan 4BTA3.9-G3 Engine
Brand: Cummins/Onan

The Cummins/Onan 4BTA3.9-G3 is a 3.9 L turbocharged and jacket water aftercooled engine rated at 1800 rpm. It powers generator sets from Cummins/Onan, including the DGCG. It holds 11.5 L (3.0 gal) of oil and 17.7 L (4.7 gal) of coolant.

Also known as: Cummins 4BTA3.9-G3

Part of the Cummins/Onan 4BTA3.9 engine family — 5 variants share parts & fitment.

3.9 L

Displacement

1800 rpm

Rated speed

11.5 L

Oil capacity

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

Engine specifications

Oil capacity	11.5 L
Coolant capacity	17.7 L
Displacement	3.9 L
Aspiration	Turbocharged and Jacket Water Aftercooled
Rated speed	1800 rpm

Generator sets powered by this engine

Cummins/Onan DGCG

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 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.
Speed/Hz Match 1469
Speed Signal Lost 121
Shutdown After Battle Short 1123
Short Circuit 1445
Remote Emergency Stop 1434
Pre-Low Oil Pressure Sensor 143
Pre-High Cool Temp 146
Power Down Failure 1417

Compiled from service & troubleshooting documentation across every generator set that uses the Cummins/Onan 4BTA3.9-G3.

Service intervals

Item	Action	Hours	Months	Notes
Charge air piping	Check	8 hr		Daily or after 8 hours
Coolant level	Check	8 hr		Daily or after 8 hours
Engine oil level	Check	8 hr		Daily or after 8 hours
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.
Air cleaner (clean if required)	Clean	50 hr		Weekly or after 50 hours; perform more often in dusty conditions
Battery charging system	Check	50 hr		Weekly or after 50 hours
Coolant heater	Check	50 hr		Weekly or after 50 hours
Exhaust condensate trap	Drain	50 hr		Weekly or after 50 hours
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
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.
Valve Lash	Adjust	1000 hr		After 1000 hours; contact an authorized service center for service
Alternator Bearings	Inspect	4000 hr	24 mo	Inspect all sealed bearings every 4000 to 4500 hours (10000 hr/2 years)
Alternator Bearings	Replace	30000 hr	60 mo	Replace all sealed bearings every 30000 hr/5 years (or if necessary after 10000 hr/2 years)
Air cleaner element	Replace		12 mo	Replace yearly or sooner if service indicator pops up; more often in dusty conditions
Generator set exercise	Test		1 mo	Exercise at least once a month for a minimum of 30 minutes at not less than 30 percent of 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
Other	Battery electrolyte specific gravity, fully charged (corrected)	1.260		corrected to 80 °F (27 °C)
Other	Battery recharge threshold specific gravity	1.215
Pressure	Idle Oil Pressure	10-30	psi	idle
Pressure	Idle Oil Pressure Shutdown Limit	8	psi	idle
Pressure	Idle Oil Pressure Warning Limit	12	psi	idle
Pressure	Idle oil pressure	69-207	kPa	idle
Pressure	Idle oil pressure shutdown limit	55	kPa	idle
Pressure	Idle oil pressure warning limit	83	kPa	idle
Pressure	Max. Allowable Exhaust Back Pressure	41	in. H2O
Pressure	Max. Fuel Inlet Restriction	4	in. Hg (13.5 kPa)
Pressure	Max. Fuel Return Restriction	10	in. Hg (33.8 kPa)
Pressure	Max. Fuel Return Restriction	20	in. Hg (67.6 kPa)
Pressure	Normal Oil Pressure	40-70	psi	normal
Pressure	Normal oil pressure	276-483	kPa
Pressure	Oil Pressure Shutdown Limit	15	psi	normal
Pressure	Oil Pressure Warning Limit	20	psi	normal
Pressure	Oil pressure shutdown limit	103	kPa
Pressure	Oil pressure warning limit	138	kPa
Resistance	Exciter rotor (matching 220-4447 parts)	0.167 or 0.180	ohms	approx. +/-10% at 68 F (20 C)
Resistance	Exciter rotor (matching 220-4448 parts)	0.180 or 0.210	ohms	approx. +/-10% at 68 F (20 C)
Resistance	Exciter stator (matching part numbers with main stator 0.0371-0.0410 range)	19.5	ohms	approx. +/-10% at 77 F (25 C)
Resistance	Exciter stator (matching part numbers with main stator 0.0561-0.0620, 0.0860-0.0950, 0.1354-0.1496)	20.3	ohms	approx. +/-10% at 77 F (25 C)
Resistance	Generator winding insulation resistance (exciter stator, exciter rotor, main rotor, main stator)	minimum 1	megohm
Resistance	Main rotor (220-4448-07, -13, -19, -31)	1.11	ohms	approx. +/-10% at 77 F (25 C)
Resistance	Main rotor (220-4448-08, -14, -20, -32)	1.20	ohms	approx. +/-10% at 77 F (25 C)
Resistance	Main rotor (220-4448-09, -15, -21, -33)	1.31	ohms	approx. +/-10% at 77 F (25 C)
Resistance	Main rotor (220-4448-10, -16, -22, -34)	1.50	ohms	approx. +/-10% at 77 F (25 C)
Resistance	Main rotor (220-4448-11, -17, -23, -35)	1.66	ohms	approx. +/-10% at 77 F (25 C)
Resistance	Main rotor (220-4448-12, -18, -24, -36)	1.80	ohms	approx. +/-10% at 77 F (25 C)
Resistance	Main rotor (220-4448-37 through -42)	2.05	ohms	approx. +/-10% at 77 F (25 C)
Resistance	Main rotor (matching 220-4447-06, -11, -16)	0.57	ohms	approx. +/-10% at 77 F (25 C)
Resistance	Main rotor (matching 220-4447-07, -12, -27)	0.64	ohms	approx. +/-10% at 77 F (25 C)
Resistance	Main rotor (matching 220-4447-08, -13, -28)	0.67	ohms	approx. +/-10% at 77 F (25 C)
Resistance	Main rotor (matching 220-4447-09, -14, -29)	0.80	ohms	approx. +/-10% at 77 F (25 C)
Resistance	Main rotor (matching 220-4447-10, -15, -30)	0.93	ohms	approx. +/-10% at 77 F (25 C)
Resistance	Main stator 220-4447-06	0.0561-0.0620	ohms	approx. +/-10% at 68 F (20 C)
Resistance	Main stator 220-4447-07	0.0466-0.0515	ohms	approx. +/-10% at 68 F (20 C)
Resistance	Main stator 220-4447-08	0.0371-0.0410	ohms	approx. +/-10% at 68 F (20 C)
Resistance	Main stator 220-4447-09	0.0228-0.0252	ohms	approx. +/-10% at 68 F (20 C)
Resistance	Main stator 220-4447-10	0.0181-0.0200	ohms	approx. +/-10% at 68 F (20 C)
Resistance	Main stator 220-4447-11	0.0860-0.0950	ohms	approx. +/-10% at 68 F (20 C)
Resistance	Main stator 220-4447-12	0.0613-0.0677	ohms	approx. +/-10% at 68 F (20 C)
Resistance	Main stator 220-4447-13	0.0480-0.0530	ohms	approx. +/-10% at 68 F (20 C)
Resistance	Main stator 220-4447-14	0.0309-0.0341	ohms	approx. +/-10% at 68 F (20 C)
Resistance	Main stator 220-4447-15	0.0261-0.0289	ohms	approx. +/-10% at 68 F (20 C)
Resistance	Main stator 220-4447-16	0.0561-0.0620	ohms	approx. +/-10% at 68 F (20 C)
Resistance	Main stator 220-4447-17	0.0428-0.0473	ohms	approx. +/-10% at 68 F (20 C)
Resistance	Main stator 220-4447-18	0.0333-0.0368	ohms	approx. +/-10% at 68 F (20 C)
Resistance	Main stator 220-4447-19	0.0228-0.0252	ohms	approx. +/-10% at 68 F (20 C)
Resistance	Main stator 220-4447-20	0.0171-0.0189	ohms	approx. +/-10% at 68 F (20 C)
Resistance	Main stator 220-4447-26	0.1354-0.1496	ohms	approx. +/-10% at 68 F (20 C)
Resistance	Main stator 220-4447-27	0.0960-0.1050	ohms	approx. +/-10% at 68 F (20 C)
Resistance	Main stator 220-4447-28	0.0713-0.0788	ohms	approx. +/-10% at 68 F (20 C)
Resistance	Main stator 220-4447-29	0.0485-0.0536	ohms	approx. +/-10% at 68 F (20 C)
Resistance	Main stator 220-4447-30	0.0404-0.0446	ohms	approx. +/-10% at 68 F (20 C)
Resistance	Main stator 220-4448-07	0.0209-0.0231	ohms	approx. +/-10% at 68 F (20 C)
Resistance	Main stator 220-4448-08	0.0162-0.0179	ohms	approx. +/-10% at 68 F (20 C)
Resistance	Main stator 220-4448-09	0.0143-0.0158	ohms	approx. +/-10% at 68 F (20 C)
Resistance	Main stator 220-4448-10	0.0095-0.0105	ohms	approx. +/-10% at 68 F (20 C)
Resistance	Main stator 220-4448-11	0.0076-0.0084	ohms	approx. +/-10% at 68 F (20 C)

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	Notes
Coolant		Refer to Cummins engine Operation and Maintenance Manual for coolant recommendations/specifications	Balanced coolant mixture of water, antifreeze and coolant additives.
Engine oil		Refer to Cummins engine Operation and Maintenance Manual for lubricating oil classification	Gensets are shipped with oil added.
Fuel	Diesel		Do not use zinc coated or copper fuel lines with diesel fuel.
Fuel	diesel		Diesel; do not use zinc coated or copper fuel lines

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
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	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.
1311	Customer Input #1		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		Warning	Optional customer selection; programmable (enable/disable, status/warning/shutdown, active open/closed, display name). Default #2 thru #4 - Warning.
1317	Customer Input #3		Warning	Optional customer selection; programmable (default #3 - Low Fuel).
1318	Customer Input #4		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 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.
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	Controller cannot power down because of an unknown condition.	Warning	Indicates controller cannot power down because of unknown condition. Possible drain on battery. Contact an authorized service center for service.
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	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	Indicates engine coolant heater is not operating or is not circulating coolant. Check coolant heater power supply for blown fuse or disconnected cord; check for low coolant level and replenish; look for coolant leaks and repair.
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.
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 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.
1448	Under Frequency	Engine speed dropped below 90% of nominal for 10 seconds.	Shutdown	Check fuel supply, intake air supply and load; check P8 connections.
1449	Over Frequency	Frequency is 10% above base frequency for 20 seconds.	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	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 Match	Measured speed and measured AC output frequency do not agree.	Shutdown	Check calibration file.
1471	Over Current	Generator output current exceeded 110% of rated for 60 seconds.	Warning	Check load and load lead connections.
1472	Over Current	Generator output current exceeded 110% of rated; time/current calculation initiated shutdown.	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.
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.
212	Oil Temp Sensor H	Engine oil temperature signal is shorted high.	Warning	Check sender/connectors/wires; check resistance between P7-22 (OIL TEMP) and P7-26 (OIL TEMP COM).
213	Oil Temp Sensor L	Engine oil temperature signal is shorted low.	Warning	Check sender/connectors/wires; check shorts and resistance between P7-22 and P7-26.
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	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 has exceeded normal operating speed.	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.
2397	S1 CB Not Open	Utility contact (S1) failed to open with PTC enabled.	Warning	Refer to Section 5.
2966	PTC Timeout	PTC module is not responding; no longer communicating (PTC status may be okay).	Warning	Check PTC status light; check cable connections between PTC module and control; cycle power.
2967	Governor Fault	Governor hardware drive circuitry contains a fault condition.	Warning	Check governor hardware drive circuitry.
2968	AVR Fault	AVR hardware contains a fault condition.	Warning	Check AVR hardware.
2969	LON Failure	No communications with LonWorks board.	Warning	Check communications with LonWorks board.
2971		No message (PTC Test Mode Active).	Info	None required; fault code only displayed in InPower.
2972	Field Overload	AVR Field has been at Max Field for a time greater than the allowed Max Field Time.	Shutdown	Check field load.
359	Fail To Start	Engine cranks but fails to start (possible fuel system problem).	Shutdown	Possible fuel system problem (engine cranks but fails to start). Check for empty fuel tank, fuel leaks, or plugged fuel lines; check for dirty fuel filter and replace if necessary; check for dirty or plugged air filter and replace if necessary; reset the control and restart.
415	Low Oil Pressure	Engine oil pressure has dropped below the shutdown trip point.	Shutdown	Indicates engine oil pressure has dropped below shutdown trip point. Check oil level. If oil level is low, replenish. 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	Indicates battery voltage supply to control is approaching a low level. Check battery charger fuse. Recharge or replace battery. Clean battery cable terminals and tighten all connections. Check battery charge voltage float level if applicable.
442	High Bat Voltage	Battery voltage supply approaching a high level at which control damage can occur.	Warning	Indicates battery voltage supply to control is approaching a high level. Check float level on battery charger if applicable (lower float level).

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.

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.

Generator/Base Board Isolation Procedure diagnostic

⚠ This test involves unregulated excitation; disconnect all loads.

⚠ HAZARDOUS VOLTAGE.

Tools: Voltmeter, 12 volt battery, Jumpers

Throw line circuit breaker OFF and shut down the set.
Remove control housing side cover; disconnect exciter stator X and XX leads from AC harness.
Prepare to measure output voltage across generator terminals while set runs.
Connect a 12V battery jumper positive (+) to X lead (Field +).
Check polarity again; polarity must be correct.
Start the set and connect battery negative (-) jumper to XX lead.
If rated output voltage or higher and all phases balanced, generator is likely OK.
If unbalanced troubleshoot main stator; if uniformly low troubleshoot exciter and field circuits.

Testing the Float Switch Assembly diagnostic

Tools: Ohmmeter, Feeler gauge

Remove fuel pump control cover, disconnect wiring jack, unscrew assembly from top of day tank.
Holding assembly vertical, test continuity between each pair of colored leads; all readings zero.
Lift each float to 1/8 inch (3 mm) below the C-clip stop and test continuity; all readings infinity.
Use pipe thread sealant when replacing the assembly.

Testing the PMG diagnostic

⚠ HAZARDOUS VOLTAGE.

Tools: Voltmeter, Wheatstone bridge or digital ohmmeter

Disconnect PMG leads PMG 2, 3 and 4 from AC harness connectors.
Start engine and let speed stabilize.
Measure voltage across PMG 2&3, PMG 3&4 and PMG 4&2.
Voltage should be at least 150 VAC (50 Hz) or 180 VAC (60 Hz) and equal.
Stop set and measure resistance across each pair; each winding approximately 4.4 ohms.

Convert Day Tank Controller 120 VAC to 240 VAC installation

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.
On control transformer, remove jumpers between H1 & H3 and H2 & H4; connect two jumpers between H2 and H3.

Convert Day Tank Controller 240 VAC to 120 VAC installation

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

Current Transformer (CT) Installation installation

⚠ Improper installation of CTs will cause a 1459 Reverse Power shutdown error.

Face the dot on the CT toward the generator (current flows into the dot).
Route CT1 on U load leads (A phase), CT2 on V load leads (B phase), CT3 on W load leads (C phase).
6-lead sets: route generator output leads through the CTs.
12-lead sets: route load wires through the CTs.
Connect CT secondary wire 1 to pin 1; 2/3 to pin 2 (high voltage) or pin 3 (low voltage).

Magnetic Speed Pickup Unit (MPU) Installation installation

⚠ Do not use fan blade to bar over engine.

Bar the engine until a flywheel gear tooth lines up in the center of the mounting hole.
Thread the sensor in gently by hand until it just touches the gear tooth.
Back it out one quarter turn and set the locknut.

Vibration Isolators Installation and Adjustment installation

Place vibration isolators on genset support structure; shim/grout so isolator bases are within 0.25 in (6 mm) of each other and level.
Loosen side snubber lock nuts so top plate moves freely; align top plate with base and springs.
Place genset onto isolators, aligning skid mounting with threaded isolator hole.
Adjust leveling bolt through skid into isolator; maintain 0.25 in (6 mm) or greater clearance between top plate and base.
Adjust leveling bolts until set is level with roughly equal clearance on all isolators, then lock leveling bolt with lock nut.
Leave snubber nuts loose for better isolation between genset and support structure.

Checking Battery Electrolyte Level maintenance

⚠ Do not add water in freezing weather unless the engine will run two to three hours to mix water and electrolyte.

Check the level of the electrolyte at least every 200 hours of operation.
Fill the battery cells to the bottom of the filler neck.
If cells are low on water, add distilled water and recharge.
If one cell is low, check the case for leaks.

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
		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)
110V - 120V L-N	Single phase, 2-wire	Jumper locations for single phase, 2-wire		PTC Module AC wiring (0300-5382-01, -02)
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
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.

Common questions

What is the oil capacity of the Cummins/Onan 4BTA3.9-G3?

The Cummins/Onan 4BTA3.9-G3 engine has an oil capacity of 11.5 liters.

What is the displacement of the Cummins/Onan 4BTA3.9-G3?

The Cummins/Onan 4BTA3.9-G3 has a displacement of 3.9 liters.

Which generators use the Cummins/Onan 4BTA3.9-G3 engine?

The Cummins/Onan 4BTA3.9-G3 powers 1 generator set(s), including Cummins/Onan DGCG.

What is a common problem with the Cummins/Onan 4BTA3.9-G3 engine?

A commonly reported issue on generators using the Cummins/Onan 4BTA3.9-G3 is: Over Current.