Name: Cummins/Onan HDKAJ Generator Set
Brand: Cummins/Onan

Service parts for the HDKAJ

Grouped by system, with how many of each the parts manual calls for.

Air intake

1 required

AF2614Air filter$75.04eBay

Fuel system

1 required

FS1006Fuel filter (primary)$29.99eBay

Oil system

1 required

FL777Oil filtersee priceAmazon

Belts

1 required

511-0235Beltsee priceAmazon

Prices captured from merchant listings; some links are affiliate links. Confirm against your serial number before ordering.

Specifications

Ratings spec sheet not in our library yet — see the documents below.

Maintenance & consumables

Item	Spec	Part #
Air filter	Element Air Cleaner, Primary	AF2614	Amazon eBay $75.04
Fuel filter	Filter, Fuel Water Separator	FS1006	Amazon $33.95 eBay $29.99
Oil filter	Filter, Oil (Skid Mounted)	FL777	Amazon eBay
Belt	Belt, Fan	511-0235	Amazon eBay

Service intervals

Item	Action	Hours	Months	Notes
Engine oil level	Check	4 hr		During break-in: check oil level twice a day or every 4 hours during the first 24 hours of operation
Engine Oil and Oil Filter	Change	150 hr		First service — Footnote 1: as part of engine break-in, change the engine oil after the first 50 hours of operation
Engine Oil and Filter	Change	150 hr		First service — Perform more often in dusty conditions; more often in hot weather; at least once a year
Coolant Anti-freeze Protection	Check	1000 hr	1 mo	Perform at least once a year
Coolant Anti-freeze Protection	Test	500 hr		Check Coolant Anti-freeze Protection
Engine Air Filter	Replace	500 hr	12 mo	Perform more often when operating in dusty environments; perform at least once a year
Fuel Filter	Replace	1000 hr		Perform every 250 hours when using B20 Bio-diesel fuel
Spark Arrestor	Clean	1000 hr	12 mo	Perform at least once a year
Coolant Pressure Cap	Replace	1000 hr	24 mo	Perform at least once every two years
Coolant System	Drain	1000 hr	24 mo	Flush coolant system; at least once every two years
Coolant System	Other	1000 hr		Flush coolant system; perform at least once every two years
Battery	Clean		1 mo	Monthly; perform more often in hot weather
Battery and connections	Clean		1 mo	More often in hot weather
Coolant hoses and thermostat	Replace	1000 hr	60 mo	Qualified mechanic required
Coolant system	Change		24 mo	Flush coolant system; footnote 5: perform at least once every two years; text states replace coolant every two years (Table 3, page 19)
Crankcase breather	Clean	1000 hr	60 mo	Qualified mechanic required
Engine V-belt	Replace	1000 hr	60 mo	Qualified mechanic required
Genset	Other	2 hr	4 mo	Storing the genset: proper storage required when idle for more than 120 days
Spark Arrester	Clean		1 mo	Monthly; perform at least once a year

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	Bore	2.64 inch (67 mm)	inch (mm)
Clearance	Stroke	2.68 inch (68 mm)	inch (mm)
Other	Actuator speed control lever stop screw (beginning Spec B)	Turn in until just makes contact, then one more full turn (rotor not in place); set locknut		Adjust whenever a different actuator base assembly is installed
Other	Altitude power derate	approximately 3 percent per 1000-foot (305 m) increase in elevation	percent
Other	Battery cable size, total cable length 0 to 10 feet (0 to 3 m)	2	AWG	temperatures down to –20°F (–29°C)
Other	Battery cable size, total cable length 11 to 15 feet (3 to 4.5 m)	0	AWG	temperatures down to –20°F (–29°C)
Other	Battery cable size, total cable length 16 to 20 feet (4.5 to 6 m)	000	AWG	temperatures down to –20°F (–29°C)
Other	Bore	2.64	inch (67 mm)
Other	Clamping screw (beginning Spec B high-idle adjustment)	Run back in by hand until snug, back it out 1-1/2 turns, set lock nut	turns	After setting high-idle speed
Other	Compression Ratio	23 : 1
Other	Compression ratio	23:1
Other	Continuous operation at up to 80 percent of maximum power	6000	watts	80% of maximum power
Other	Cooling system capacity	4.2 quart (4 l)	quart (l)	includes coolant recovery tank
Other	Displacement	44	inch3 (719 cc)
Other	Displacement	44 inch3 (719 cc)	inch3 (cc)
Other	Fuel and oil line fittings sealant	Use liquid-type pipe thread sealant sparingly on male threads only; do not use teflon tape on pipe fittings		Flare fittings: do not use any thread sealant
Other	Fuel flow rate (minimum)	200 ml (0.4 pints) per minute	ml/min	Fuel flow test while priming
Other	Fuel pump flow	200	ml/min	minimum
Other	Fuel pump flow rate	not less than 200	ml per minute	during prime
Other	Fuse F1 (control circuit)	10	ampere mini-bayonet
Other	Fuse F2 (starter solenoid circuit)	10	ampere mini-bayonet
Other	Fuse F3 (glow plug circuit)	25	ampere
Other	Generator set air intake temperature vs ambient (hot air recirculation test)	3-6	°C (5-10 °F) above ambient, maximum	90-minute run test under 3/4+ load
Other	Genset length x width x height	36.3 x 23.6 x 22.3 inch (922 x 599 x 566 mm)	inch (mm)
Other	Genset weight (wet)	420 lbs (191 kg)	lbs (kg)
Other	Governor actuator rotor travel	about 1/2 inch (12 mm)	inch	Push rotor clockwise by hand against fuel rack return spring; should rotate and return smoothly
Other	Maximum Regulated-Voltage Battery Charging Current (Optional)	10	ampere
Other	Maximum fuel pump lift	36	inches (914 mm)
Other	Postheat timing	0-5	seconds	Coolant temp dependent
Other	Postheat timing (glow plugs)	0 sec (coolant temp > 70 deg F); 5 sec (coolant temp < 70 deg F)	sec	Following start disconnect
Other	Preheat timing	0-15	seconds	Coolant temp dependent
Other	Preheat timings (glow plugs)	0 sec (coolant temp > 120 deg F); 5 sec (50 deg F); 10 sec (23 deg F); 15 sec (< -4 deg F)	sec	Coolant temperature dependent
Other	Rated cranking current	180	amperes	at 0°F (–18°C)
Other	Stroke	2.68	inch (68 mm)
Pressure	Cooling System Pressure Cap	14	psi
Pressure	Cooling system pressure	14	psi	Proper cooling system pressure essential for optimal engine cooling and minimal coolant loss
Pressure	Cooling system pressure (pressure cap)	14	psi
Pressure	Engine oil pressure (minimum acceptable)	14 psi (98 kPa)	psi	After engine has run a few minutes; replace low oil pressure cutoff switch if 14 psi or greater, service engine if less
Pressure	Engine oil pressure (minimum)	98	kPa	Replace switch if ≥14 psi (98 kPa)
Pressure	Engine oil pressure gauge, normal reading	approximate center of scale		during operation
Pressure	Engine oil quantity for oil change refill	3 quart (2.6 l)	quart (l)
Pressure	Exhaust back pressure under full load	2	inches water column (51 mm WC)	measured within 6 inches (153 mm) of the muffler outlet flange
Pressure	Low oil pressure switch threshold / minimum engine oil pressure	98	kPa	after engine has run a few minutes
Pressure	Oil Pressure	Approximate center of scale		Operating
Resistance	Current transformer resistance	15 to 25	ohms
Resistance	Governor actuator coil resistance	1.7 to 2.8	ohms
Resistance	PMA winding preliminary check	approximately 1	ohm	Digital ohmmeter, lowest scale, across winding lead pair
Resistance	Stator main winding T1-1 - T2-1	1 ± 0.15	Ω	@ 25 °C (77°F)
Resistance	Stator main winding resistance (T1-1 to T2-1, T1-1 to T3-1, T2-1 to T3-1, T1-2 to T2-2, T1-2 to T3-2, T2-2 to T3-2)	1 ± 0.15	ohm	@ 25 °C (77 °F), ±15%
Resistance	Stator winding insulation resistance	at least 5 megohms	megohms	New stator with dry windings; 500 VDC megger; at least 1 megohm for genset in service; polarization index at least 2
Resistance	Stator winding insulation resistance (in service)	>1	megohm
Resistance	Stator winding insulation resistance (in service)	at least 1	megohm	PI of 2
Resistance	Stator winding insulation resistance (new stator)	greater than 5	megohms	PI at least 2
Resistance	Stator winding insulation resistance (new)	>5	megohms
Resistance	Stator winding resistance (lead pair to lead pair)	0.997-1.219	ohms	At 70 deg F (21 deg C); T1-1/T2-1, T3-1/T2-1, T1-1/T3-1, T1-2/T2-2, T3-2/T2-2, T1-2/T3-2
Speed	High-idle speed	3500-3600	RPM
Speed	High-idle stop screw speed	3550-3590	rpm	while holding actuator fully clockwise
Speed	High-idle stop screw speed (Spec A prior to 1997)	3525	rpm	Actuator held fully clockwise
Speed	High-idle stop screw speed (Spec A prior to 1997)	3550-3590	rpm
Speed	Idle speed	3500-3600	rpm

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	50/50 mixture ethylene glycol anti-freeze and water	Contains rust and corrosion inhibitor; no stop-leak additive	above -37°C	4.0 l	4.2 quart (4 l) capacity; suitable down to -34 F (-37 C)
Coolant	50/50 mixture of ethylene glycol anti-freeze and water as shipped; use ethylene or propylene glycol anti-freeze solution containing rust and corrosion inhibitor	Anti-freeze must not contain a stop-leak additive; water must be clean, low in minerals and free of corrosive chemicals; use distilled water if available	above -37°C	4.0 l	Factory fill suitable down to -34 deg F (-37 deg C); cooling system capacity 4.2 quart (4 l) includes coolant recovery tank; replace coolant every two years
Coolant	50/50 mixture of ethylene glycol anti-freeze and water; ethylene or propylene glycol solution containing rust and corrosion inhibitor	No stop-leak additive; use clean, low-mineral water, distilled if available	above -37°C	4.0 l	Suitable for temperatures down to -34° F (-37° C); cooling system capacity 4.2 quart (4 l) including coolant recovery tank; replace coolant every two years
Coolant	50/50 mixture of ethylene glycol antifreeze and water		above -37°C	4.0 l	Suitable for temperatures down to –37 °C (–34 °F); antifreeze should be fully formulated with rust inhibitors and coolant stabilizers, mixed with fresh (distilled) water
Coolant	Ethylene or propylene glycol anti-freeze, 50/50 mixture		above -34°C	4.2 quart	Must contain rust and corrosion inhibitor; no stop-leak additives
Coolant	50/50 mixture of ethylene glycol anti-freeze and water	Ethylene or propylene glycol anti-freeze solution containing rust and corrosion inhibitor; must not contain a stop-leak additive; water clean, low in minerals, free of corrosive chemicals, distilled if available	above 37°C	4.2 quart (4 l)	Factory fill suitable for temperatures down to -34 F (-37 C); replace coolant every two years
Coolant	Ethylene glycol antifreeze, fully formulated with rust inhibitors and coolant stabilizers		above 37°C	4.0 l (4.2 qt) incl. recovery tank	50/50 mixture recommended for all climates
Engine oil	SAE viscosity grade chosen from Chart 1 (Oil Viscosity vs. Temperature) for ambient temperatures expected until next oil change	API performance Class CH-4, CG-4 or CF-4, may be in combination with SJ, SH or SG (e.g. CH-4/SJ)		2.6 l	3 quart (2.6 l) with filter
Engine oil	SAE viscosity grade per Chart 1 (Oil Viscosity vs. Temperature)	API CH-4, CG-4 or CF-4 (may combine with SJ, SH or SG)		2.6 l	3 quarts (2.6 l) capacity with filter
Engine oil	SAE viscosity grade per Chart 4-1 (oil viscosity vs. temperature)	API performance Class CH-4, CG-4 or CF-4D, may be combined with SJ, SH or SG (e.g. CH-4/SJ)		2.6 l	Oil capacity with filter 3 quart (2.6 l)
Engine oil	SAE viscosity grade selected per anticipated ambient temperature (Chart 1, Oil Viscosity vs. Temperature)	API performance Class CH-4, CG-4 or CF-4, may be in combination with performance Class SJ, SH or SG (e.g. CH-4/SJ)		3.0 quart (2.6 l)	Oil capacity with filter; change oil if not appropriate for ambient temperatures during break-in
Engine oil	Performance Class CH-4, CG-4 or CF-4		-40°C to 40°C	3.0 quart	Select SAE grade based on ambient temperature; see oil viscosity chart
Engine oil	5W-30	API CF, CF-4, CG-4, CH-4, or CI-4	-28°C to 10°C
Engine oil	10W-30 10W-40	API CF, CF-4, CG-4, CH-4, or CI-4	-18°C to 27°C
Engine oil	15W-40 (OnaMax)	API CF, CF-4, CG-4, CH-4, or CI-4	-12°C to 38°C		Multigrade oils such as SAE 15W-40 are recommended for year round use
Engine oil	SAE 30	API CF, CF-4, CG-4, CH-4, or CI-4	above 0°C		0 °C (32 °F) and higher
Engine oil	10W-30 / 10W-40	API CF/CF-4/CG-4/CH-4/CI-4	18°C to 27°C	2.6 l (3 qt)
Fuel	Bio-diesel blends B5 – B20	ASTM D7467 (blend), ASTM D6751 or EN14214 (bio-diesel component), ASTM D975 (petroleum diesel component)			Water separator required in fuel line just before generator set; purge with pure ASTM D975 diesel for minimum 30 minutes before storage over 90 days
Fuel	Diesel				Diesel fuel
Fuel	No. 1 diesel fuel (ASTM 1-D)	ASTM 1-D	below 0°C		Use when the outdoor ambient temperature is below freezing; Cetane number of at least 45 for reliable starting
Fuel	No. 2 Diesel (ASTM 2-D) above freezing; No. 1 Diesel (ASTM 1-D) below freezing	Cetane number at least 45
Fuel	No. 2 diesel (ASTM 2-D) above freezing; No. 1 diesel (ASTM 1-D) below freezing	Cetane number of at least 45
Fuel	No. 2 diesel fuel (ASTM 2-D) above freezing; No. 1 diesel fuel (ASTM 1-D) below freezing	ASTM 2-D / ASTM 1-D; Cetane number of at least 45 for reliable starting			Use clean, fresh fuel
Fuel	No. 2 diesel fuel (ASTM 2-D) in ambients above freezing; No. 1 diesel fuel (ASTM 1-D) in ambients below freezing	ASTM 2-D / ASTM 1-D; Cetane number of at least 45 for reliable starting			Diesel fuel is combustible; keep ignition sources away
Fuel	No. 2 diesel fuel (ASTM 2-D) when outdoor ambient temperature is above freezing; No. 1 diesel fuel (ASTM 1-D) when below freezing	Cetane number of at least 45 for reliable starting			Engine is certified to operate on diesel fuel
Fuel	No. 2 diesel fuel (ASTM 2-D)	ASTM 2-D	above 0°C		Use when the outdoor ambient temperature is above freezing; Cetane number of at least 45 for reliable starting
Other	Water for engine coolant	Clean, low in minerals, free of corrosive chemicals; use distilled water if available

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
1	High Temperature (first-level fault)	Engine coolant temperature exceeded 115°C (239°F) for 10 seconds	Shutdown	Touch Stop to check the second-level fault code; it will be either No. 33 or No. 34.
11	Overcurrent Fault	Inverter short circuit indicated for >3 counts.	Shutdown	Turn off the genset line circuit breaker; if the genset no longer shuts down, check for and repair a short in vehicle appliances, wiring or shorted battery charger transformer; check whether vehicle engine and genset share the same starting battery and increase battery capacity or install a separate battery.
12	Over Voltage	The control is unable to maintain rated voltage.	Shutdown	If the vehicle engine and genset share a starting battery, increase battery capacity or install a separate battery and charging system for the genset.
13	Under Voltage	The control is unable to maintain rated voltage.	Shutdown	Reduce load (especially air conditioners and battery chargers).
14	Over Frequency	The engine governor is unable to maintain rated frequency.	Shutdown	Reduce the number of connected appliances, especially when air conditioners and battery chargers are running.
15	Underfrequency Fault	The engine governor is unable to maintain rated frequency.	Shutdown	Reduce the number of connected appliances; have air conditioners and other appliances checked for proper operation (a locked compressor rotor can cause very low power factor).
17	Fuel Pump Fault	Controller sensed open circuit; bypassable fault prior to Spec F, discontinued beginning Spec F	Shutdown	Try priming by holding control switch at Stop; reconnect fuel pump leads; test pump on 12 V battery; check P1-2/E2-1 and E2-2/ground continuity.
18	Glow Plug Circuit Protection Fault	Controller sensed short circuit; bypassable fault prior to Spec F, discontinued beginning Spec F	Shutdown	Reconnect HR-1 to glow plug bus bar; check HR-1 and A1-J8 for ground short; replace engine harness or control assembly.
19	Governor Actuator Fault	The control sensed an open or shorted circuit.	Shutdown	See an authorized Onan dealer.
2	Low Oil Pressure (first-level fault)	The low oil pressure cutoff switch did not open.	Shutdown	Check oil level; check switch and wiring; replace switch or service engine if pressure <14 psi (98 kPa).
21	Starter Solenoid Circuit Protection Fault	Controller sensed short circuit; discontinued beginning Spec F	Shutdown	Reconnect K-1 to starter solenoid; test solenoid and starter; reconnect A1-J6; check continuity to ground; replace controller assembly.
22	Governor Overload	The duration of operation is near full-duty cycle beyond design limit.	Warning	Step 01 (0.5 hr): check load, air intake restriction, exhaust restriction, air leak in fuel system, stator for opens/shorts. Step 02 (1.0 hr): check fuel flow test, governor for binding, high idle adjustment, injectors, injection pump timing, compression (SRT 00-0BL)
23	Low Oil Pressure Cutoff Switch Fault	Switch still open during start - not a running fault	Shutdown	See an authorized Onan dealer.
24	Faulty Temperature Sender	Did not sense temperature change during first 5 minutes	Shutdown	See an authorized Onan dealer.
25	Engine Above Speed Target Fault	Governor unable to regulate to target speed.	Shutdown	See an authorized Onan dealer.
26	Engine Below Speed Target Fault	Governor unable to regulate to target speed.	Shutdown	Step 01 (0.5 hr): check loads, air in fuel system, air intake restriction, exhaust restriction. Step 02 (1.0 hr): check binding in the governor, high idle speed, injectors, injection timing, compression (SRT 00-0BQ)
27	Voltage Sense	The control is unable to sense output voltage.	Shutdown	Test with load bank to isolate load; check PMA-to-control connections; measure PMA lead voltages (T1-T2, T2-T3, T3-T1 - should exceed 20 Vrms); troubleshoot rotor/stator; replace control assembly.
28	DC Sense Lost Fault	Controller unable to sense DC bus voltage	Shutdown	Open the circuit breaker; if the fault does not persist, check for and disconnect excessive loads from the genset before starting.
29	High Battery Voltage Fault	Voltage across the battery system is greater than 19 Volts.	Warning	Check battery connections; measure DC voltage; check battery charger; verify ground at P1-7.
3	Service Check Fault (first-level fault)	Service fault; see second-level fault code.	Warning	Touch Stop to check the second-level fault code; it will be one of the codes in the troubleshooting table.
31	Overspeed Fault	Engine speed greater than 3600 rpm.	Shutdown	See an authorized Onan dealer.
32	Low Cranking Speed Fault	Cranking speed less than 180 rpm for more than 2 seconds; crank and generator frequency less than 3 Hz for greater than 2 seconds	Shutdown	Step 01 (0.3 hr): check fuse, harness connections to starter, battery connections at set and battery, battery voltage at set. Step 02 (0.7 hr): check starter operation, harness connection for opens/shorts, stator resistance for opens/shorts, rotor magnets for failure (SRT 00-0BS)
33	High Engine Coolant Temperature Fault	Maximum coolant temperature is 230°F (110°C), at which point the genset will shut down and fault code No. 33—High Engine Coolant Temperature—will be displayed by the status indicator light.	Shutdown	Step 01 (0.5 hr): verify FC is actually a secondary code; verify coolant level and fill if needed; verify engine coolant temperature; air inlet/outlet opening for blockage; excessive coach loads; coolant pump belt for wear; cooling fan for damage; housing air leaks. Step 02 (0.5 hr): check temperature sensor lead for opens/shorts; radiator blockage and clean. Step 03 (2.0 hr): clean and flush coolant system; replace coolant thermostat (SRT 00-0CS)
34	High Inverter Temperature Fault	Inverter heat sink temperature exceeded design limit.	Shutdown	Remove objects blocking the air inlet or outlet openings; reduce the number of appliances connected at the same time.
35	Control Card Fault	Microprocessor EPROM error during self-test.	Shutdown	Verify problem and report to factory (SRT 00-0CA, 0.2 hours)
36	Unknown Shutdown Fault	The engine stopped without receiving a command from the control.	Shutdown	Step 01 (0.3 hr): check fuel level in coach tanks, prime genset fuel system, air filter blockage, mechanical damage. Step 02 (0.5 hr): check auxiliary fuel pump, conduct fuel flow test, P1 and P2 connectors and wiring (SRT 00-0BW)
37	Invalid Genset Configuration Fault	The generator set control is not configured properly for the generator set	Shutdown	Verify problem and report to factory (SRT 00-CHA, 0.2 hours)
38	Overcurrent Fault	Too many loads connected.	Shutdown	Step 01 (0.2 hr): reduce coach loads, cool inverter. Step 02 (1.0 hr): check if set has engine performance issue, fuel supply for sucking air, fuel flow test, governor operates smoothly, high idle speed, current transformer for shorts/opens (SRT 00-0BX)
39	Low Battery Voltage Fault	Prior to Spec F only	Warning	Inspect connections; check fuel/air leaks; avoid cranking propulsion engine; check battery voltage; replace/recharge battery.
4	Overcrank	Set cranked for 35 seconds without starting (speed >1200 RPM) (Begin Spec K)	Shutdown	Troubleshoot as an out-of-fuel condition (see FC36); check fuel flow and return, actuator operation, wiring.
41	Generator Rotor	Control unable to sense field or output voltage	Shutdown	Contact local dealer or distributor.
42	Processor Fault	Microprocessor ROM error during self-test; beginning Spec F and replacement controller assemblies	Shutdown	Verify fault code (SRT 00-0CB, 0.2 hours)
43	Processor Fault	Microprocessor RAM error during self-test; beginning Spec F and replacement controller assemblies	Shutdown	Verify fault code (SRT 00-0CC, 0.2 hours)
45	Speed Sense	The control is unable to sense quadrature frequency.	Shutdown	Contact local dealer or distributor.
46	Inverter Power Supply Fault	Low battery voltage or power supply device failure; beginning Spec F and replacement controller assemblies	Shutdown	Verify fault code, voltage at set during cranking, voltage at starter during cranking, battery connections at set and battery, battery condition, set charging system if equipped (SRT 00-0BZ, 0.5 hours)
48	Generator Field Sense	The control is unable to sense field voltage.	Shutdown	Contact local dealer or distributor.
57	Over Prime	Priming exceeded 3 minutes.	Shutdown	Check for and remove any object holding either control switch in the STOP/PRIME position.
8	Overload (Models HDKAH & HDKAV only)	Models HDKAH & HDKAV only: load exceeded 110 percent of rating for 2 minutes	Shutdown	Reduce load and restart.

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

Procedures

Governor Actuator Speed Control Lever Stop Adjustment (Spec B and later) adjustment

Loosen the stop screw locknut and back the screw out a few turns.
Turn the stop screw in until it just makes contact.
Turn the screw 1 full turn further in and set the locknut (rotor not in place procedure).
Alternatively with actuator in place: loosen set screw locknut, turn stop screw in until just makes contact, set locknut.

High-Idle Speed Adjustment adjustment

⚠ Do not let engine speed exceed 3600 RPM.

Tools: tachometer

Remove front housing panel.
Set up tachometer.
Remove actuator cover and reattach leads.
Start generator set and push actuator rotor clockwise fully (about 12 mm).
Adjust high-idle speed to 3500-3600 RPM.
For Spec A, adjust screw; for Spec B, adjust screws and set locknut.
Let rotor go; generator should stop and display fault code.
Restart and recheck high idle speed.

Valves − Adjust, All adjustment

Remove and install cover and panels, valve cover
Adjust valve lash
Test run unit

Voltage Adjustment adjustment

⚠ Touching uninsulated live parts can cause severe injury or death.

Tools: voltmeter

Start generator set; allow voltage and frequency to stabilize 3-5 seconds.
Rapidly press Start switch 6 times within first minute to enter voltage adjust mode.
To increase: press and quickly release Start switch; each press increases about 0.6 volts.
To decrease: press and hold Start switch about 1 second; each press decreases about 0.6 volts.
Repeat until desired voltage.
Wait 20 seconds for amber light to stop blinking.
Press Stop switch to save adjustment.

Fuel Flow Test diagnostic

Tools: Graduated quart (1 liter) or larger container

Disconnect fuel return hose from line to supply tank; point end into a quart (1 liter) or larger graduated container.
Hold Start/Stop switch in STOP for the duration of the test.
Flow should not be less than 200 ml (0.4 pints) per minute.

Fuel Pump Test diagnostic

Tools: container

Disconnect fuel return hose and point into container.
Prime generator set by holding Start/Stop in STOP.
Flow should not be less than 200 ml per minute.
If low, replace fuel filter, check restrictions, air bubbles, filter body, or fuel pump.

Hot Air Recirculation Test diagnostic

⚠ Exhaust gas is deadly; do not run indoors or where exhaust can accumulate

Tools: Thermocouples (24 AWG max), PVC pipe thermocouple shield

Complete a representative installation.
Conduct test in a well-ventilated space protected from cross drafts.
Connect a large constant load, at least 3/4 full load if a load bank is available.
Measure generator set intake air temperature and ambient air temperature with shielded thermocouples (24 AWG).
Close all compartment doors and run generator set at least 90 minutes, recording temperatures at 15-minute intervals.

Starter Solenoid Test diagnostic

⚠ High currents, arcing, and moving parts.

Tools: jumper cables, vise

Secure starter motor assembly in vise.
Connect motor terminal on solenoid to positive 12V battery.
Connect one end of negative cable to battery negative.
Briefly touch other end of negative cable to motor mounting flange.
If motor does not spin quickly, replace starter motor; if it does, replace solenoid.

Temperature Test diagnostic

⚠ To prevent severe scalding, always let the engine cool down before removing the coolant pressure cap. Turn the cap slowly, and do not open it fully until the pressure has been relieved.

Tools: thermocouples, 2 inch diameter by 6 inch long white PVC pipe or equivalent shield, new hose clamp

Conduct the test at a location where the ambient air temperature will remain between 60°F and 100°F (16°C and 38°C) during the test.
Connect the genset to a load bank that can be adjusted to apply full rated load.
Run the genset under full-load, with all service and compartment doors closed, and record temperatures every 15 minutes until they stabilize.
Measure temperatures with thermocouples not heavier than No. 24 AWG (0.21 mm2) at the locations shown in Figure 18.
Locate a shielded thermocouple in the center of the air inlet opening of the genset to measure inlet air temperature.
Locate a shielded thermocouple within 48 inches (1.2 meters) of the inlet air opening and at the same height to measure ambient air temperature.
Locate a thermocouple on the oil dip stick to measure oil temperature; it should not extend past the ball on the end of the dip stick.
Relieve coolant system pressure, remove the coolant hose from the thermostat outlet, secure a thermocouple so the bead is in the center of the thermostat outlet fitting, run leads out, and secure the

Troubleshoot − Battery Not Charging diagnostic

Check battery connections and battery condition (0.2 hr)
Perform checks in step 01 (0.8 hr): check circuit breaker, wiring connections, continuity of transformer, DC regulator

Troubleshoot − Coolant Loss (External) diagnostic

Check coolant level, cracked or leaking hoses, loose hose clamps, radiator for leaks, coolant in oil (0.4 hr)
Perform checks in step 01 (1.0 hr): pressure test coolant system; run generator set and check for leaks

Troubleshoot − Engine Cranks But Will Not Start (Genset) diagnostic

Check fuel level, prime fuel system, air in fuel system, air filter restriction, glow plug fuse (0.5 hr)
Perform checks in step 01 (0.7 hr): check connections at glow plug bus, resistance of each glow plug, fuel pump, B+ at glow plugs

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 oil filter does the Cummins/Onan HDKAJ use?

The Cummins/Onan HDKAJ uses oil filter part number FL777.

Which fuel filter part number does the Cummins/Onan HDKAJ take?

The Cummins/Onan HDKAJ uses fuel filter part number FS1006.

What air filter fits the Cummins/Onan HDKAJ?

The Cummins/Onan HDKAJ uses air filter part number AF2614.

Troubleshooting

Fault codes

Code	Meaning
Code 1	Engine Over Temperature
Code 2	Low Oil Pressure
Code 3	Service Check
Code 4	Over Crank
Code 12	Over Voltage
Code 13	Under Voltage

Fault codes and symptom→remedy steps extracted from this model’s service/owner documentation; verify against the official manual before servicing. Full Cummins/Onan HDKAJ troubleshooting guide (11 entries) →

Repair guides

− Changes to the repair procedure

Step-by-step procedures compiled from the Cummins/Onan service manual for this model.

Parts

Part #	Description	Qty	System
122-0833	Filter, Oil	1	Oil filter	Amazon $15.99 eBay $19.99 FridayParts $20.19
149-2513	Filter, Fuel	1	Fuel filter	Amazon $15.99 eBay $36.95 FridayParts $48.61
149-2790	Pump, Fuel	1	Pump	Amazon eBay $98.00 FridayParts $24.89
185-5433	Pump, Water	1	Pump	Amazon eBay $35.45 FridayParts $44.80
185-5458	Thermostat	1	Thermostat	Amazon eBay
185-5715	Impeller	1	Impeller	Amazon eBay
185-6120	Gasket, Cylinder Head	1	Gasket	Amazon eBay
337-3782	Plug, Glow	3	Glow plug	Amazon eBay
511-0235	Belt, Fan	1	Belt	Amazon eBay
541-0530	Installation of Auxiliary Fuel Pump Kit on Commercial HDKAJ, HDKAK Generator Set 1 (G300)		Fuel pump	Amazon eBay
541-0531	Installation of Remote Air Cleaner Kit on Commercial HDKAJ, HDKAK Generator Set 1 (G299)		Air filter	Amazon eBay
AF2614	Element Air Cleaner, Primary	1	Air filter	Amazon eBay $75.04
AF2615	Element Air Cleaner, Secondary	1	Air filter	Amazon eBay
FL3325	Filter, Oil (On Engine)	1	Oil filter	Amazon eBay
FL777	Filter, Oil (Skid Mounted)	1	Oil filter	Amazon eBay
FS1006	Filter, Fuel Water Separator	1	Fuel filter	Amazon $33.95 eBay $29.99
100-3707	Engine Replacement HDKAH/J/K Spec A	1	Service part / kit	Amazon eBay
185-6704	Block Assy Cylinder (Includes Parts Marked *) Spec A	1	Service part / kit	Amazon eBay
A043T622	Recommended Spares List (RSL) for RV Generator Set (HDKAJ, HDKAK)	1	Service part / kit	Amazon eBay

Service, wear & replacement parts referenced for this model and its engine — confirm the exact part for your serial number. See the full parts catalog to search and cross-reference.

Fuel consumption

Load	L/h	gal/h
	0.49	0.13
50%	1.85	0.49
100%	3.03	0.8

Available documents

Operator's manual (Cummins/Onan)Operator's manual — 981-0161 Onan HDKAx (spec L-M) RV Genset Operator manual (03-2010) (Cummins/Onan)Operator's manual — 981-0161C Onan HDKAH HDKAJ HDKAK HDKAT HDKAU HDKAV Mobile Genset Operator's manual (07-2006) (Cummins/Onan)Operator's manual — Onan - Generator Model HDKAH (Spec A-R), HDKAJ (Spec A-K), HDKAK (Spec A-R) Operator Manual (Cummins/Onan)Owner's manual (Cummins/Onan)Owner's manual — 981-0161B Onan HDKAJ HDKAK HDKAT HDKAU Mobile Genset Operator's manual (08-2005) (Cummins/Onan)Service manual (Cummins/Onan)Service manual — 0981-0522-i32-hdkax-service-manual (Cummins/Onan)Service manual — 900-0615B Onan HDKAJ HDKAK Repair Times (Cummins/Onan)Service manual — 981-0522B Onan HDKAJ HDKAK HDKAT Mobile Genset Service Manual (07-1999) (Cummins/Onan)Service manual — 981-0623 Onan HDKAJ HDKAK HDKAT Mobile Genset Installation manual (08-1999) (Cummins/Onan)Service manual — 981-0623B Onan HDKAJ HDKAK (spec A-H) HDKAT HDKAU (spec A-E) Diesel Mobile Genset Installation manual (08-2005) (Cummins/Onan)Service manual — A046L051 (Cummins/Onan)Service manual — A046L053 (Cummins/Onan)Service manual — HDKAH, HDKAJ, HDKAK, HDKAU, HDKAV Service Manual (Cummins/Onan)