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Cummins/Onan 6AT3.4 Engine

The Cummins/Onan 6AT3.4 is a turbocharged engine rated at 1800 rpm. It powers generator sets from Cummins/Onan, including the DGAE. It holds 11.4 L (3.0 gal) of oil and 17.5 L (4.6 gal) of coolant.

Also known as: 6AT3.4, Cummins/Onan 6AT3.4

1800 rpm

Rated speed

11.4 L

Oil capacity

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

Engine specifications

Oil capacity	11.4 L
Coolant capacity	17.5 L
Aspiration	Turbocharged
Rated speed	1800 rpm

Generator sets powered by this engine

Cummins/Onan DGAE

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

Common problems

Engine will not crank.
Cause: Fault lamp on.
Fix: Correct fault and reset control.
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. FAULT 1
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.
The fault lamp lights. Engine shuts down immediately, engine runs for several seconds and then shuts down, or engine continues to run. FAULT 1 or FAULT 2
Fix: Engine gauges show oil pressure, engine temperature, and frequency (speed) are within normal limits.
SWITCH OFF lamp flashes.
Cause: Indicates Run/Stop/Remote switch is in the Stop position which will prevent automatic starting if an automatic transfer switch is used.
Fix: Move the Run/Stop/Remote switch to the Remote position for automatic starting.
Same features as Fault 1 (Normally set for non-timed shutdown). FAULT 2 (red)
PRE LO OIL PRES lamp lights. Engine continues to operate.
Cause: Indicates engine oil pressure has dropped to 20 psi (138 kPa).
Fix: If generator is powering critical loads and cannot be shut down, wait until next shutdown period and then follow step 5 procedure. If engine can be stopped, follow procedures in step 5.
PRE HI ENGINE TEMP lamp lights. Engine continues to operate.
Cause: Indicates engine has begun to overheat and engine temperature has risen to approximately 202°F (94°C).
Fix: If generator is powering non-critical and critical loads and cannot be shutdown, use the following: Reduce load if possible by turning off non-critical loads; Check air inlets and outlets and remove any obstructions to airflow; Open doors or windows in generator area to increase ventilation. If engine can be stopped, follow procedure in step 3.
OVERCRANK lamp lights and engine stops cranking. or Engine runs, shuts down, and LO OIL PRES lamp lights.
Cause: Indicates possible fuel system problem.
Fix: Check for empty fuel tank, fuel leaks, or plugged fuel lines and correct as required; Check for dirty fuel filter and replace if necessary (see MAINTENANCE section); Check for dirty or plugged air filter and replace if necessary (see MAINTENANCE section); Refer to Step 5; Reset the control and restart after correcting the problem. Contact an authorized dealer or distributor for service if none of the above.
NO AC output voltage.
Cause: Field breaker is tripped.
Fix: Reset breaker. Contact an authorized dealer or distributor if voltage build up causes breaker to trip.
LO OIL PRES lamp lights. Engine shuts down
Cause: Indicates engine oil pressure has dropped to 14 psi (97 kPa).
Fix: Check oil level, lines and filters. If oil system is okay but oil level is low, replenish. Reset control and restart. Contact an authorized dealer or distributor if oil pressure is not in the range of 30 to 55 psi (206 to 379 kPa).
LO FUEL lamp lights. Engine shuts down and LO OIL PRES lamp lights.
Cause: Indicates engine has run out of fuel.
Fix: 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.
LO ENG TEMP lamp lights. Set is in standby mode but is not operating. (Lamp lights when engine coolant temperature is 70°F (21°C) or lower. Since the lamp goes out after the engine warms up, there should be no cause for alarm even during initial generator set operation.)
Cause: Indicates engine coolant heater is not operating or is not circulating coolant.
Fix: Check for the following conditions: Coolant heater not connected to power supply. Check for blown fuse or disconnected heater cord and correct as required; Check for low coolant level and replenish if required. Look for possible coolant leakage points and repair as required; Contact an authorized dealer or distributor if none of the above.
HI ENG TEMP lamp lights. Engine shuts down.
Cause: Indicates engine has overheated (engine temperature has risen above 222°F/106°C) or coolant level is low (sets with coolant level sensor).
Fix: Allow engine to cool down completely before proceeding with the following checks: Check coolant level and replenish if low. Look for possible coolant leakage points and repair if necessary; Check for obstructions to cooling airflow and correct as necessary; Check for a slipping fan belt and tighten if loose; Reset control and restart after locating and correcting problem. Contact an authorized dealer or distributor if none of the above.
Green RUN lamp lights following engine start-up.
Cause: Indicates all engine systems are normal.
Fix: No corrective action required.

Compiled from service & troubleshooting documentation across every generator set that uses the Cummins/Onan 6AT3.4.

Service intervals

Item	Action	Hours	Months	Notes
Crankcase oil	Change	50 hr		First service — After first 50 hours of operation on new generator sets.
Valve lash clearance	Check	50 hr		First service — See Note 3; perform after first 50 hours of operation on new sets.
Battery electrolyte level	Check	200 hr		Check at least every 200 hours of operation.
Crankcase breather cap (turbo)	Clean	400 hr		DGAE turbocharged engines; clean with solvent and allow to dry.
Generator bearing	Inspect	1000 hr		Inspect for evidence of outer case rotation every 1000 hours.
Cooling system	Drain		12 mo	Drain, flush, and refill once a year.
Generator bearing	Replace	10000 hr	60 mo	Standby: every five years.

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	Trailer brake actuator stroke length	1	inch (25 mm)	maximum before brake shoe readjustment
Gap	Float switch test feeler gauge	0.125	inch (3 mm)	between float and C-clip stop
Gap	Magnetic pickup adjustment	1/2 turn out from tooth	turn	after contact with flywheel tooth
Gap	Overspeed switch air gap	0.005	inch (0.13 mm)	minimum
Gap	Overspeed switch air gap	not less than 0.005	inch (0.13 mm)
Other	Battery charge threshold	1.215		charge if reading is below
Other	Battery electrolyte specific gravity	1.260	specific gravity	fully charged at 80°F (27°C)
Other	Battery electrolyte specific gravity	about 1.260	specific gravity	fully charged at 80°F (27°C)
Other	Battery specific gravity fully charged	1.260		corrected to 80°F (27°C)
Other	Brake shoe adjustment	10	clicks	back off from point wheel cannot be turned by hand
Other	Control heater element power	75	watts at 120 VAC
Other	Cooling system fill rate	3	gallons/minute
Other	Cycle cranking	15 seconds crank, 15 seconds rest, 3 cycles	seconds	12-lamp control
Other	Fan belt tension	60	lbs (267 N)
Other	Heavy duty air cleaner air drying time	24	hours	minimum
Other	Overcrank cranking limit	75	seconds
Pressure	Engine oil pressure (normal)	30 to 55	psi (207 to 380 kPa)	engine at operating temperature
Pressure	Low oil pressure shutdown	14	psi (97 kPa)
Pressure	Low oil pressure shutdown	below 14	psi (97 kPa)	fault time delayed about 10 seconds following starter disconnect and inhibited during cranking
Pressure	Pre-low oil pressure alarm	20	psi (137 kPa)	or less
Resistance	Actuator coil resistance	1 ±10%	ohm	at 77°F (25°C); leads disconnected
Resistance	Control heater element resistance	192	ohms	dissipates 75 watts at 120 VAC
Resistance	Exciter rotor winding resistance	0.54	ohms	at 77°F (25°C), ±10%
Resistance	Exciter rotor winding resistance	0.54 ±10%	ohms	at 77°F (25°C)
Resistance	Exciter rotor winding resistance	0.645	ohms	at 77°F (25°C), ±10%
Resistance	Exciter rotor winding resistance	0.645 ±10%	ohms	at 77°F (25°C)
Resistance	Exciter stator insulation resistance to lamination	100,000	ohms	minimum; 500 VDC or more
Resistance	Exciter stator winding resistance	12.4 ±10%	ohms	at 77°F (25°C)
Resistance	Exciter stator winding resistance	14.5 ±10%	ohms	at 77°F (25°C)
Resistance	Exciter stator winding resistance, 4A2.3/6A3.4/6AT3.4	14.5	ohms	at 77°F (25°C), ±10%
Resistance	Exciter stator winding resistance, DGAB/DGAC/DGAD/DGAE	12.4	ohms	at 77°F (25°C), ±10%
Resistance	Exciter stator winding resistance, DL4	20.0	ohms	at 77°F (25°C)
Resistance	Exciter stator winding resistance, DL6	25.0	ohms	at 77°F (25°C)
Resistance	Exciter stator winding resistance, DL6T	40.0	ohms	at 77°F (25°C)
Resistance	Governor actuator coil resistance	1 ±10%	ohms	at 77°F (25°C); resistance to case infinity
Resistance	Insulation resistance to ground	100,000 or greater	ohms	500 VDC or more megger; exciter stator/rotor and main rotor/stator
Resistance	Magnetic pickup DC resistance	175 ±15%	ohms	at 77°F (25°C); disconnected from terminals 5 and 6
Resistance	Magnetic pickup coil resistance	175 ±15%	ohms	at 77°F (25°C); leads to case infinity
Resistance	Main rotor insulation resistance to shaft	100,000	ohms	minimum; 500 VDC or more
Resistance	Main rotor resistance at stack length 10.50 in (267 mm)	2.55	ohms	at 77°F (25°C) ±10%
Resistance	Main rotor resistance at stack length 5.88 in (149 mm)	2.75	ohms	at 77°F (25°C) ±10%
Resistance	Main rotor resistance at stack length 7.12 in (181 mm)	1.80	ohms	at 77°F (25°C) ±10%
Resistance	Main rotor resistance at stack length 8.75 in (222 mm)	2.04	ohms	at 77°F (25°C) ±10%
Resistance	Main rotor winding resistance, stack length 10.50 in (267 mm)	2.55	ohms	at 77°F (25°C), ±10%
Resistance	Main rotor winding resistance, stack length 10.50 in (267 mm), QSA-series	2.91	ohms	at 77°F (25°C), ±10%
Resistance	Main rotor winding resistance, stack length 5.88 in (149 mm)	2.75	ohms	at 77°F (25°C), ±10%
Resistance	Main rotor winding resistance, stack length 7.12 in (181 mm)	1.80	ohms	at 77°F (25°C), ±10%
Resistance	Main rotor winding resistance, stack length 7.12 in (181 mm), QSA-series	1.98	ohms	at 77°F (25°C), ±10%
Resistance	Main rotor winding resistance, stack length 8.75 in (222 mm)	2.04	ohms	at 77°F (25°C), ±10%
Resistance	Main rotor winding resistance, stack length 8.75 in (222 mm), QSA-series	2.24	ohms	at 77°F (25°C), ±10%
Resistance	Main stator insulation resistance	100,000	ohms	minimum; 500 VDC or more
Resistance	QSA main rotor resistance at stack length 10.50 in (267 mm)	2.91	ohms	at 77°F (25°C) ±10%
Resistance	QSA main rotor resistance at stack length 5.12 in (130 mm)	2.55	ohms	at 77°F (25°C) ±10%
Resistance	QSA main rotor resistance at stack length 5.88 in (149 mm)	2.75	ohms	at 77°F (25°C) ±10%
Resistance	QSA main rotor resistance at stack length 7.12 in (181 mm)	1.98	ohms	at 77°F (25°C) ±10%
Resistance	QSA main rotor resistance at stack length 8.75 in (222 mm)	2.24	ohms	at 77°F (25°C) ±10%
Resistance	Transformer TX1 coil resistance	370; 313	ohms	at 77°F (25°C), within ±10%; no continuity between windings or to ground
Resistance	Transformer TX1 winding resistance	313	ohms	within ±10% at 77°F (25°C)
Resistance	Transformer TX1 winding resistance	370	ohms	within ±10% at 77°F (25°C)
Speed	Engine speed equivalent of frequency	30	r/min per Hz

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	Ethylene glycol antifreeze (permanent type) and clean water; 50/50 mixture		Use soft water; contains rust and corrosion inhibitor; no stop-leak additive. Capacities: DGAB 11.5 L (12.2 QT); DGAC/DGAD 16.8 L (17.8 QT); DGAE 17.5 L (18.5 QT).
Engine oil	API CD/SF or CE/SF; multigrade	API CD/SF or CE/SF	Preferred oil grades per Table 5-2; choose grade for lowest expected temperature. Capacities: DGAB 5.7 L (6 QT); DGAC/DGAD 8.5 L (9 QT); DGAE 11.4 L (12 QT).
Fuel	ASTM 2-D (No. 2 Diesel) or ASTM 1-D (No. 1 Diesel)	Minimum Cetane number 45	Use No. 1 diesel when ambient temperatures are below 0°C (32°F) and during long periods of light load. Low sulfur; cloud point at least 10 degrees below lowest expected fuel temperature.
Other	DOT 3		Trailer brake system; reservoir should be at least half full
Other	DOT-3 heavy duty hydraulic fluid		Trailer brake system bleeding
Other	distilled water		Battery electrolyte; add distilled water to maintain proper level.

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

Fault codes

Code	Name	Meaning	Severity	Action
FAULT 1	Fault 1	Undedicated fault; may be programmed as shutdown or non-shutdown and as timed or non-timed; normally set for timed shutdown.		Investigate optional fault selection; contact dealer if needed.
FAULT 2	Fault 2	Undedicated fault; same features as Fault 1; normally set for non-timed shutdown.		Investigate optional fault selection; contact dealer if needed.
HI ENG TEMP	High engine temperature shutdown	Engine shut down because coolant temperature rose above 222°F (106°C) or coolant level is low.	Shutdown	Allow to cool; check coolant level, airflow, and fan belt; reset and restart; contact dealer if fault persists.
LO FUEL	Low fuel	Fuel supply marginally low.	Warning	Check fuel supply and replenish.
LO PRES	Low oil pressure shutdown	Engine shut down because oil pressure dropped below 14 psi (97 kPa).	Shutdown	Check oil level, lines, and filters; reset and restart; contact dealer if pressure is not 30 to 55 psi.
LOW ENG TEMP	Low engine temperature	Engine temperature marginally low for starting; indicates inoperative coolant heater. Lamp lights when engine coolant temperature is 70°F (21°C) or lower.	Warning	Check coolant heater power, fuse, cord, and coolant level; contact dealer if fault persists.
LOW OIL PRES	Low oil pressure shutdown	Red lamp indicates engine shutdown because of critically low oil pressure.	Shutdown	Check oil level and LOP switch; inspect engine.
OVERCRANK	Overcrank shutdown	Starter locked out because of excessive cranking time.	Shutdown	Check fuel system, fuel filter, and air filter; reset and restart; contact dealer if fault persists.
OVERSPEED	Overspeed shutdown	Engine shut down because of excessive speed.	Shutdown	Contact authorized dealer or distributor for service.
PRE HI ENG TEMP	Pre-high engine temperature	Engine temperature marginally high, 202°F (94°C).	Warning	Reduce load if possible, check airflow, and improve ventilation; if engine can be stopped follow high engine temperature procedure.
PRE HIGH ENG TEMP	Pre-high engine temperature	Yellow lamp indicates engine temperature is marginally high.	Warning	Find and correct cause.
PRE LO OIL PRES	Pre-low oil pressure	Oil pressure marginally low, 20 psi (137 kPa) or less.	Warning	Find and correct cause as soon as possible.
RUN	Run	All engine systems normal.	Info	No corrective action required.
SWITCH OFF	Switch off	Generator set is not in automatic start operation mode.	Warning	Move Run/Stop/Remote switch to REMOTE for automatic starting.

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

Procedures

Adjust magnetic pickup adjustment

Tools: Compressed air, Jam nut wrench

Rotate engine so ring gear tooth is centered in MPU hole.
Clean mounting hole with compressed air.
Turn MPU in until it contacts flywheel tooth directly below.
Turn out 1/2 turn and lock with jam nut.
Be sure pickup does not rotate when tightening jam nut.

Adjust voltage adjust potentiometer R21 adjustment

⚠ Contact with high voltage can cause severe personal injury or death.

Tools: Insulated screwdriver

Loosen locking nut of R21 and adjust to mid-range.
Start genset and bring temperature to normal.
With no load, turn Phase Selector to read output voltage and current.
Adjust R32 for approximate desired voltage.
Fine-adjust with R21 and tighten locking nut without changing setting.

Adjust voltage regulator adjustment

⚠ Use insulating mat or dry wood platform when control doors are open.

Tools: Insulated screwdriver, Accurate voltmeter

Open control panel doors and set S1, S2, and S3 per table.
Connect accurate voltmeter to TB1-2 and TB1-3 if no AC meter.
Start genset and bring temperature to normal.
Turn R32 to set no-load voltage.
Stop genset and close control panel doors.

Calibrate electronic governor adjustment

⚠ Keep hands and fingers clear while performing tests on operating equipment.

Tools: Tachometer or frequency meter

Check actuator linkage does not bind through full travel.
Attach tachometer or frequency meter.
Set GAIN adjustment to second mark from zero.
Disconnect governor rod from throttle lever.
Start genset and adjust right stop to 72 Hz for 60 Hz gensets.
Adjust left stop to take up slack and tighten locknut.
Stop, attach governor rod, start, and adjust SPEED to 60 or 50 Hz.
Connect load and adjust GAIN clockwise until stable.

Electronic governor adjustment/calibration adjustment

⚠ Contact with rotating machinery can cause severe personal injury or death.

Tools: Tachometer or frequency meter, Screwdriver

Check actuator linkage does not bind through full travel; ensure terminals 7 and 8 are jumpered.
Attach tachometer to engine or frequency meter to generator if control panel lacks one.
Set Controller GAIN adjustment to second mark from zero.
Disconnect governor rod from throttle lever.
Place Run/Stop/Remote switch in Run position to start genset.
Adjust right stop screw on mechanical governor to obtain 72 Hz (2160 r/min) for 60 Hz gensets or 62 Hz (1860 r/min) for 50 Hz gensets.
Adjust left stop screw to just take up slack, then tighten locknut without binding shaft.
Stop genset, attach governor rod to throttle lever, start, and adjust Controller SPEED screw for 60 Hz or 50 Hz.
Connect full rated load; if genset cannot manage load, shorten governor rod one-half turn and repeat; tighten locknuts.
Connect 1/4 rated load; turn GAIN screw clockwise until actuator hunts, then back off until stable.
Stop genset, wait 30 seconds for turbo coast down if equipped, restart, and check for speed overshoot.
Restart genset and check frequency and stability under various loads.
Stop genset and remove tachometer or frequency meter if attached.

Fan Belt Adjustment adjustment

Loosen alternator bolt passing through elongated slot in mounting bracket.
Slide alternator until fan belt tension is 60 lbs (267 N).
Tighten alternator mounting bolt to lock alternator in place.
Check tension and repeat if necessary.

Voltage adjust potentiometer R21 adjustment

⚠ Contact with high voltage can cause severe personal injury or death.

Tools: Screwdriver

Loosen locking nut of R21 on control front panel and adjust R21 to mid-range.
Start genset and operate to bring temperature to normal.
With no load, turn Phase Selector switch to read output voltage/current.
Adjust R32 on voltage regulator for approximate desired voltage.
Fine-adjust voltage with R21; tighten locking nut carefully without changing setting.
Move Phase Selector switch to Off, stop genset, and set control for standby readiness.

Voltage regulator adjustment adjustment

⚠ Contact with high voltage can cause severe personal injury or death.

Tools: Insulated screwdriver, Accurate voltmeter

Open control panel doors and set S1, S2, S3 per correct stability range and mode.
With AC meter option use panel meter; without it connect accurate voltmeter to regulator TB1-2 and TB1-3.
Start genset and operate to bring temperature to normal.
Using insulated screwdriver, turn R32 potentiometer to increase or decrease no-load voltage to proper setting.
Stop genset, close control doors, and set control for operation readiness.

Control switch check diagnostic

Tools: Ohmmeter

Remove battery B+ cable.
Place ohmmeter across switch contacts.
Open and close switch while observing ohmmeter; normally open should show infinite open and continuity closed; normally closed opposite.

Fuel solenoid check diagnostic

Tools: Jumper wire

Remove harness B+ lead connection from fuel solenoid and jumper separate B+ connection to terminal.
Injection pump should click.
If no click is heard, replace fuel solenoid.

Relay check diagnostic

Tools: Voltmeter, 12 VDC source

Connect 12 VDC across relay coil terminals; relay should activate if coil is okay.
Connect 12 VDC to one side of relay contacts.
Connect voltmeter between other side of contacts and 12-volt source; 12 volts when relay energized indicates contact is okay.

Solenoid check diagnostic

Tools: Voltmeter, Jumper wires

Apply battery positive (B+) to terminal marked S.
Jumper a ground wire to solenoid ground bracket; solenoid should activate.
If contacts are good, 12 VDC should be read between terminal 1 and ground; voltage drop across contact should not exceed one volt.

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
208 VAC		Switch S1 position 1	stator T7 and T8	Transformer TX1 primary H1-H3
240 VAC		Switch S1 positions 2 and 3	stator T7 and T8	Transformer TX1 primary H3-H5

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 6AT3.4?

The Cummins/Onan 6AT3.4 engine has an oil capacity of 11.4 liters.

Which generators use the Cummins/Onan 6AT3.4 engine?

The Cummins/Onan 6AT3.4 powers 1 generator set(s), including Cummins/Onan DGAE.

What is a common problem with the Cummins/Onan 6AT3.4 engine?

A commonly reported issue on generators using the Cummins/Onan 6AT3.4 is: Engine will not crank.. Cause: Fault lamp on.. Fix: Correct fault and reset control..