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Cummins/Onan QSJ999G Engine

The Cummins/Onan QSJ999G is a 1 L 2-cylinder naturally aspirated engine rated at 3600 rpm. It powers generator sets from Cummins/Onan, including the RS13A, RS13A C13N6H, RS17A and RS17A C17N6H.

Also known as: Cummins QSJ999G

1.0 L

Displacement

Cylinders

3600 rpm

Rated speed

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

Engine specifications

Displacement	1.0 L
Cylinders	2
Aspiration	Naturally aspirated
Rated speed	3600 rpm

Generator sets powered by this engine

Cummins/Onan RS13A Cummins/Onan RS13A C13N6H Cummins/Onan RS17A Cummins/Onan RS17A C17N6H Cummins/Onan RS20A Cummins/Onan RS20A C20N6H Cummins/Onan RS20AC C20N6HC

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

Service intervals

Item	Action	Hours	Months	Notes
Engine Oil Level	Check	24 hr		Also check daily during power outages, or monthly without power outages.
Engine Oil and Oil Filter	Change	200 hr	24 mo	First service — First 25 hours.
Complete System Test	Test	200 hr	24 mo	Must be performed by a qualified service technician; see transfer switch manual.
Engine Air Filter	Replace	200 hr		Perform more often in dusty conditions.
Engine Valve Clearance	Adjust	200 hr	24 mo	Must be performed by a qualified service technician.
Starting Battery	Clean	200 hr		Clean and check starting battery.

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
Gap	Spark Plug Gap	0.7 - 0.8	mm (0.027 - 0.031 in)
Pressure	Fuel Shutoff Solenoid Coil Voltage Threshold	10.2	VDC	while attempting to start
Pressure	Fuel supply pressure (LP)	7-11	in H2O
Pressure	Fuel supply pressure (Natural gas)	5-11	in H2O
Pressure	Lubricating Oil Pressure at Rated Speed (Minimum)	310	kPa (45 psi)	at rated speed
Pressure	Maximum Fuel Supply Pressure (either fuel)	3.2	kPa (13 inch water column)	under any condition
Pressure	Natural Gas Fuel Supply Pressure	3.5 - 12	inch water column (0.9 - 3.0 kPa)
Pressure	Propane Vapor Fuel Supply Pressure	1.5 - 3.0	kPa (6 - 12 inch water column)
Resistance	Governor Actuator Resistance	2.8 ±5%	Ohms
Resistance	Rotor Ground Resistance	> 1 megohm on megger, or infinity on an ohmmeter	megohm
Resistance	Rotor Winding Resistance F1 to F2 (13 kW)	26 +/-10%	Ohms	at 75 °F room temperature
Resistance	Rotor Winding Resistance F1 to F2 (17/20 kW)	30.5 +/-10%	Ohms	at 75 °F room temperature
Resistance	Sense L1(W) - Sense L2(V) (13 kW)	0.24 +/-10%	Ohms
Resistance	Sense L1(W) - Sense L2(V) (17/20 kW)	0.107 +/-10%	Ohms
Resistance	Stator Ground Resistance	> 1 megohm on megger, or infinity on an ohmmeter	megohm
Resistance	Stator Winding Resistance L1 to N (13 kW)	0.112 +/-10%	Ohms	at 75 °F room temperature
Resistance	Stator Winding Resistance L1 to N (17/20 kW)	0.042 +/-10%	Ohms	at 75 °F room temperature
Resistance	Stator Winding Resistance Q1 to Q2 (13 kW)	2.56 +/-10%	Ohms	at 75 °F room temperature
Resistance	Stator Winding Resistance Q1 to Q2 (17/20 kW)	1.45 +/-10%	Ohms	at 75 °F room temperature
Speed	Rated RPM	3600	rpm
Temperature	Alternator Temperature Switch Contacts Open	197 - 210	°F (92 - 99 °C)
Torque	AC Battery Charger Screws	0.9 - 1.2	Nm
Torque	Access Panel Fasteners (oil drain)	5.0 - 6.6	Nm
Torque	Air-Fuel Mixer Flange Bolts	13	ft-lb (17.5 Nm)
Torque	Airbox Cover Bolts	3.2 - 4.0	Nm
Torque	Airbox Mounting Brackets Bolts	3.2 - 4.0	Nm
Torque	Airbox to Mixer/Throttle Body Nuts	3.2 - 4.0	Nm
Torque	Alternator Fan/Rotor Retention Nut	113 - 139	Nm
Torque	Alternator Ground Strap to Skid Bolt	5 - 6.2	Nm
Torque	Alternator Ground Strap/B- to End Bell Bolt	12.3 - 15	Nm
Torque	Alternator Heater	18 - 22	Nm
Torque	Alternator Leads into Circuit Breaker	4 - 5	Nm
Torque	Alternator Leads into Circuit Breaker: Bonding Jumper	4 - 5	Nm
Torque	Alternator Leads into Circuit Breaker: Neutral Lead/Lug Bolt	5.5 - 6.5	Nm
Torque	Alternator Leads into Circuit Breaker: Neutral Lug Hex Screw	4 - 5	Nm
Torque	Battery Charge Alternator Mounting Bolts	8 - 12	Nm
Torque	Battery Tray Bolt	3.2 - 4	Nm
Torque	Brush Block Access Panel (Plastic) Bolt	3.2 - 4	Nm
Torque	Brush Block Bolts	2.3 - 3.2	Nm
Torque	Control Board Bracket to Enclosure Bolt	9.8 - 11.9	Nm
Torque	Control Board to Bracket Mounting Bolt	2.8 - 3.5	Nm
Torque	Crankcase Reed Valve Cover Bolts	8 - 12	Nm
Torque	Cylinder Head Bolts	50	Nm	tighten in pattern shown
Torque	Dipstick (Shipped Separately)	9.8 - 11.9	Nm
Torque	Enclosure Hood Hinge Assembly Bolts	5.6 - 6.6	Nm
Torque	Enclosure M6 Bolts - All Panel Connections and Cross Bars	5.6 - 6.6	Nm
Torque	Exhaust Baffle to Muffler Clamp Nuts	13.9 - 16.8	Nm
Torque	Exhaust Manifold Nuts	33 - 40	Nm
Torque	Flywheel Nut	90 - 105	Nm
Torque	Governor Actuator Bracket to Engine Bolts	5.0 - 6.2	Nm
Torque	Governor Actuator Mounting Bolts	9.8 - 11.9	Nm
Torque	Head Bolts	50 - 55	Nm
Torque	Hood Latch Bolt	5.6 - 6.6	Nm
Torque	Inner Enclosure Panel to Skid Nuts/Bolts	5.6 - 6.6	Nm
Torque	Intake Manifold Nuts	11 - 14	Nm	Locking feature of nut faces outward
Torque	Isolator Bolts - Alternator	24 - 29	Nm
Torque	Isolator Bolts - Engine	24 - 29	Nm
Torque	Lower Fuel System Mounting Bolts	9.8 - 11.9	Nm
Torque	Mixer Fuel Inlet Fitting/Lock Nut	58.3 - 77.3	Nm
Torque	Muffler Mounting Bolts	9.8 - 11.9	Nm

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
Engine oil	0W30	Full synthetic gasoline engine oil which meets or exceeds API service SN/SN-RC and ILSAC GF-5		2.3 L	All temperatures, required below -17 °C (0 °F)
Engine oil	5W30	Full synthetic gasoline engine oil which meets or exceeds API service SN/SN-RC and ILSAC GF-5	above -17°C	2.3 L	Temperatures above -17 °C (0 °F)
Engine oil		Automotive-style lubrication system	-7°C to 50°C	2.3 L	Oil cooler and spin-on filter included
Fuel	LP vapor	Nominal fuel rating 93 MJ/M3 (2500 Btu/ft3)			Fuel supply pressure LP 7-11 in H2O
Fuel	Natural gas	Nominal fuel rating 37 MJ/M3 (1000 Btu/ft3)			Fuel supply pressure NG 5-11 in H2O

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
2	Low Oil Pressure Fault	Continuous ground (greater than or equal to 3 seconds) at the generator set control for oil pressure input. The switch opens the control circuit with pressure.	Shutdown	Measure the oil level; disconnect the oil pressure switch and measure continuity from P1-6 and GND; verify switch operation; measure oil pressure with a mechanical gauge; repair or replace relief valve and oil pump if necessary.
4	Overcrank	The generator set control did not sense alternator quad winding frequency after cycle crank (30 seconds of cranking and 15 seconds between each crank attempt for a total of 3 crank attempts).	Shutdown	Check fuel supply, air/fuel mixture, ignition system, starter, battery and wiring. Check air filter and exhaust. Measure quad voltage during cranking and winding resistances.
12	Overvoltage	Instantaneous Fault: AC voltage S1-S2 greater than 300 VAC. Delayed Fault: AC voltage line-to-line greater than 268 VAC but less than 300 VAC for 3 continuous seconds.	Shutdown	Measure AC voltage at the circuit breaker and pins P1-34/P1-35. Cycle loads. Reseat P1. Measure field, quadrature and main winding resistance.
13	Undervoltage	AC voltage 240 line-to-line is less than 216 VAC for 5 continuous seconds.	Shutdown	Measure AC voltage and frequency. Balance loads within 10% line-to-line. Reseat P1. Measure winding resistance and check brush alignment.
14	Overfrequency	Instantaneous Fault: Frequency greater than 72 Hz. Delayed Fault: Frequency greater than 66 Hz but less than 72 Hz for 6 continuous seconds.	Shutdown	Measure AC current and frequency. Check exhaust, fuel supply, governor actuator, demand regulator and throttle plate. Measure winding resistance and check brush alignment.
15	Underfrequency	Frequency less than 54 Hz (for the 60 Hz model) for 8 continuous seconds.	Shutdown	Measure AC current, frequency and load capability. Check air filter, exhaust, fuel supply, governor and ignition. Measure winding resistance and check brush alignment.
19	Governor Actuator Shutdown	Controller sensed governor actuator circuit is open or shorted.	Shutdown	Measure and verify governor actuator resistance (2.8 Ohms ±5%). Verify governor wiring to the control. Replace if necessary.
22	Governor Actuator Overload	Maximum governor output (PWM) for 10 continuous seconds.	Shutdown	Measure AC current. Check air filter, fuel supply, intake manifold and gaskets, exhaust and ignition. Verify the actuator function and check the governor linkage.
27	Voltage Sense Lost	The generator set frequency is greater than 40 Hz and voltage sensed is less than 5 VAC on one or both lines.	Shutdown	Measure the AC voltage. Reseat P1. Measure field, quadrature and main winding resistance. Check brush alignment.
29	High Battery Voltage	DC voltage to controller greater than 19 VDC.	Shutdown	Measure DC voltage at the battery, at the generator set and at connector P1. Measure DC voltage with the battery charger turned on and diagnose the faulty charger.
32	Low Cranking Speed Sense	Quadrature frequency is less than 1 Hz (engine RPM is less than 180) for 3 continuous seconds after pressing start.	Shutdown	Check battery and connections. Verify engine and alternator rotation. Check J1 pins. Measure DC voltage at the starter. Check air filter, exhaust, fuel supply and ignition.
35	Control Card Failure	EEPROM (programming variables) error during self-test.	Shutdown	Replace the control.
36	Generator Set Stopped Without Fault Condition	RPM is less than 500 and sense voltage S1-S2 is at 0 VAC and no other fault condition occurred.	Shutdown	Verify engine and alternator rotation. Check air filter, exhaust, fuel supply, governor and ignition. Measure winding resistance.
37	Invalid Set Configuration	Generator set control configuration does not meet any valid configuration.	Shutdown	Using the display, reset and save the generator set configuration. If correct and the fault will not clear, replace the control.
43	Processor Fault	RAM (programming variables) error during self-test.	Shutdown	Replace the control as necessary.
45	Speed Sense Fault	While running, the quadrature frequency dropped to 0 Hz for 1 continuous second.	Shutdown	Inspect and clean slip rings. Measure quadrature winding resistance between P1-2 and P1-3. Check harness continuity. Measure frequency and droop.
46	Generator Set Overload	The total generator set load is above 105% of rated.	Shutdown	Measure the AC current and voltage while running with all connected loads. Identify faulty or short cycling loads and reduce loads as necessary.
76	Alternator Over Temp	The temperature at the alternator is too high. The high temperature switch opens between 197 - 209 °F (91.5 - 98.5 °C). An open condition on this circuit triggers the fault.	Shutdown	Verify the air inlet and air outlet panels are not obstructed. Measure the temperature sensor wiring (P1-33 to GND) for continuity. Inspect the cooling fan.

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

Procedures

Converting the Fuel System Type adjustment

⚠ Do not rotate the center section of the valve beyond the detent.

Tools: 6 mm external hex wrench

From the Main screen, select Menu; hold the Next key at least 5 seconds to view the Config Menu.
Highlight 'Config' and click Enter. Use the Next key to navigate to the Fuel Type field; select NG or LP.
Do not change the number in the Config field.
Use a 6 mm external hex wrench to rotate the center section of the fuel valve.
Turn the center section clockwise until the detent is reached; do not rotate beyond this point.
Keep selecting the Back button to save the settings and return to the Main screen.

Generator Config Screen Setup adjustment

⚠ Failure to configure will result in Fault Code 37.

From the Main screen, select Menu.
Press and hold the Next key on the Menu screen for at least 5 seconds to view the Config Menu.
Highlight 'Config' and click the Enter key. The Generator Config screen appears.
Use the Next key to navigate to the Config field. Use the arrow keys to select the appropriate config option (20 = C20N6H/C20N6HC, 21 = C17N6H, 22 = C13N6H).
Use the Next key to navigate to the Fuel Type field. Select NG (natural gas; default) or LP (liquid propane).
Keep selecting the Back button to save the settings and return to the Main screen.

Fuel Shutoff Solenoid Troubleshooting diagnostic

Tools: Multi-meter, Soapy water solution

Disconnect the four harness leads from the fuel solenoid coils.
Check that battery voltage is being supplied through the generator set harness using a multi-meter between FSOL1+/FSGND1 and FSOL2+/FSGND2 while trying to start.
Verify that the voltage is 10.2 VDC. If no voltage, check for bad wiring; if less than 10.2 VDC, check for bad wiring or discharged battery.
Check for proper solenoid operation by applying 12 VDC to a coil and listening/feeling for activation. Repeat for all solenoids.
If either solenoid does not activate, replace the gas valve assembly.
Check for fuel leaks at the solenoid with a soapy water solution on pipe threads and around the base; tighten or replace as required.

Line Circuit Breaker Troubleshooting diagnostic

⚠ Automated Machinery: accidental or remote starting can cause severe personal injury or death.

Tools: Ohmmeter

Shut down and disable the generator set; disconnect the negative (–) battery cable and reconnect it last when done.
Disconnect the leads going into and out of the circuit breaker (two leads from the alternator at the top L1 and L2, and two from customer wiring at the bottom L1 and L2).
Check continuity: with the breaker on, very low resistance between the L1 lugs and between the L2 lugs.
With the breaker off, the continuity check between L1 and L2 pairs should show open.
Replace the breaker if either of the continuity tests fails.

Testing the Alternator diagnostic

⚠ Disconnect the AVR before doing any insulation resistance test. Discharge the windings by shorting to earth through an earthing rod for at least 5 minutes.

Tools: Ohmmeter, Megger or insulation resistance meter, Wheatstone bridge (0.001 Ohms precision)

Test the rotor for grounded, open and shorted windings using an ohmmeter, testing at the brush block terminals first.
For rotor ground resistance, set the ohmmeter to the highest scale or use a megger; touch one probe to the rotor shaft and the other to a slip ring.
For rotor winding resistance, connect each meter test lead to a separate slip ring and compare to the resistance table.
Test for a short between the main windings and the quad windings.
For stator ground resistance, touch one test probe to the stack and, in turn, the other to each stator lead.
Measure stator winding resistance with a meter having precision down to 0.001 Ohms.
Measure each winding to the stator laminations to check for bad insulation.

Adding Oil maintenance

⚠ Ensure that the generator set engine has cooled down before adding or draining the oil.

Ensure that the oil fill cap area is clean, and prevent debris from entering the engine.
Add the appropriate amount of oil, based on the engine oil level check.
Recheck the engine oil level. Based on the results, add or drain oil.
Clean up and dispose of any oil in accordance with local/state regulations.

Brush Block/Slip Ring Service maintenance

⚠ Make sure the brushes are aligned correctly with the slip rings; otherwise they may break when the generator set is started.

Tools: Scotch Brite pad or commutator stone

Disconnect the field leads from the brush block (F1, F2).
Remove the two mounting screws.
Withdraw the brush block from the alternator end bell.
Inspect the brush block: if either brush is shorter than 11 mm (7/16 inch), binds, or is damaged, replace the brush block assembly.
When installing the brush block, keep the brushes retracted with the wire through the hole; remove the wire after bolting the block in place.
If the slip rings have grooves, pits, or other damage, use a Scotch Brite pad or commutator stone to remove light wear or corrosion.

Changing Engine Oil and Oil Filter maintenance

⚠ Contact with used engine oil can cause cancer or reproductive toxicity.

⚠ Accidental or remote starting can cause severe personal injury or death.

Open the generator set's circuit breaker to prevent the ATS from transferring to generator set source when manually starting.
Manually start the generator set and allow it to run 2 to 5 minutes to warm the engine oil.
Remove the access panels to get to the drain hose.
Stop the generator set and allow it to thoroughly cool. Disconnect the battery charger and the negative (–) battery cable.
Open the oil drain cap to release oil from the engine into the appropriate container, close it, and wipe it clean.
Place an appropriate container below the oil filter. Remove the oil filter by turning it counterclockwise and remove the old gasket.
Clean the filter mounting surface on the engine block.
Make sure the gasket is in place on the new filter and apply a thin film of clean oil to the gasket.
Install the new filter until the gasket just touches the block. Turn it an additional 1/2 to 3/4 turn. Do not over-tighten.
Add the appropriate amount of oil and check the engine oil level.
Reconnect the battery cables, positive (+) cable first, and reconnect the battery charger.
Operate the generator set with no load for approximately 5 minutes to check for leaks at the oil filter or oil drain hose.
Shut down the generator set, wait 5 minutes, and confirm the correct oil level. Check for leaks and repair any identified.
Dispose of the used oil and oil filter according to local environmental regulations.
Re-install the access panels and restore the original generator set settings, then close the generator set breaker.

Checking Engine Oil Level maintenance

⚠ Do NOT check oil while the generator set is operating.

⚠ Overfilling can cause foaming or aeration of the oil.

Make sure that the generator set has not been running for approximately five minutes.
Clean off the area surrounding the dipstick port and prevent debris from entering the engine.
Pull out the dipstick and wipe it clean.
Reinsert and fully seat the dipstick.
Remove the dipstick and check the oil level.
Reinsert and fully seat the dipstick.

Draining Excessive Oil maintenance

Remove the access panels to get to the drain hose.
Place the end of the drain hose into an appropriate container.
Open the oil drain cap to release oil from the engine into the appropriate container.
Re-check the engine oil level. Based on the results, add or drain oil.
When a sufficient amount of oil has been drained, close the oil drain cap and wipe it clean.
Re-install the access panels. Torque the fasteners 3.5 - 5.0 ft-lb (5.0 - 6.6 Nm).
Dispose of the used oil in accordance with local and state regulations.

Immobilize the Generator Set maintenance

⚠ Accidental or remote starting of the generator set can cause severe personal injury or death.

Tools: Insulated wrench, E-Stop button

Press the Off switch from the display and then press the E-Stop button to shut down the engine.
Thoroughly ventilate the generator set before disconnecting any leads.
Turn off and disconnect the heater (where fitted) from the AC source before disconnecting the battery cables.
Turn off and disconnect the battery charger (where fitted) from the AC source.
Turn off the fuel supply to the engine.
Disconnect the battery. Disconnect the negative (–) cable first, using an insulated wrench.
Place warning notices at each location that state, 'Maintenance in Progress – Immobilized for Safe Working.'

Clock Setup operation

From the Main screen, select Menu. Use the arrow keys to highlight Clock. Select the Enter key.
Use the arrow keys to set the time and date. Select the Next key to go to the Daylight Savings screen.
Use the arrow keys to enable/disable Daylight Savings. If enabling, select Next to highlight the Offset field.
Use the arrow keys and Next key to set the offset value for Daylight Savings time.
Select Next to set when Daylight Savings starts: set Month (1 – 12), Week (0 – 5), Day (Sun – Sat) and Hour (12AM – 12PM).
Select Next to set when Daylight Savings ends using the same fields.
Keep selecting the Back button to save the settings and return to the main screen.

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
115/230	1	Split phase		Available on RS14AF model at 50 Hz
120/240	1	Split phase		Available on RS20A and RS20AC models at 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 displacement of the Cummins/Onan QSJ999G?

The Cummins/Onan QSJ999G has a displacement of 1.0 liters with 2 cylinders.

Which generators use the Cummins/Onan QSJ999G engine?

The Cummins/Onan QSJ999G powers 7 generator set(s), including Cummins/Onan RS13A, Cummins/Onan RS13A C13N6H, Cummins/Onan RS17A, Cummins/Onan RS17A C17N6H, Cummins/Onan RS20A.