Cummins/Onan HDKAJ — Specs, Engine, Parts & Maintenance

Service parts for the HDKAJ

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

Air intake

1 required

140-2897Air filter$19.99eBay

Fuel system

1 required

149-2513Fuel filter$31.59NAPA

Oil system

1 required

122-0833Oil filter$9.64NAPA

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	Air filter	140-2897	Amazon eBay $19.99 FridayParts $48.61
Fuel filter	Fuel filter	149-2513	Amazon eBay $36.95 NAPA $31.59 FridayParts $48.61
Oil filter	Oil filter	122-0833	Amazon eBay $19.99 NAPA $9.64 FridayParts $20.19
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	Engine Over Temperature	Engine coolant temperature exceeded 115°C (239°F) for 10 seconds	Shutdown	Check coolant level and add if needed; check for blockages/dirt on radiation fins; reduce load
2	Low Oil Pressure	Low oil pressure cutoff switch did not open	Shutdown	Check engine oil level, add or drain as needed
3	Service Check	Second-level service fault; flash STOP/PRIME once for 2-digit code	Warning	See second-level fault code
4	Over Crank	Cranking exceeded 30 seconds without engine starting	Shutdown	Check fuel level and prime; check air filter; replace oil with proper viscosity; check fuel fittings; replace fuel filter
8	OVERLOAD	Load exceeded 110% of genset rating for 2 minutes (HDKAH & HDKAV models)	Shutdown	Reduce load and restart
11	OVERCURRENT FAULT	AC output short	Shutdown	Turn off line breaker; check for short circuits in appliances or wiring
12	Over Voltage	Control unable to maintain rated voltage	Shutdown	Contact local dealer or distributor
13	Under Voltage	Control unable to maintain rated voltage	Shutdown	Reduce load (air conditioners, battery chargers)
14	Over Frequency	Engine governor unable to maintain rated frequency	Shutdown	Contact local dealer or distributor
15	Under Frequency	Engine governor unable to maintain rated frequency	Shutdown	Reduce load
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 continuity to ground; replace engine harness or controller assembly.
19	Governor Actuator	Control sensed an open or shorted circuit	Shutdown	Contact local dealer or distributor
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 Actuator Overload	Duration of operation near full-duty cycle beyond design limit	Shutdown	Reduce load; check air filter; check exhaust system for blockage
23	LOW OIL PRESSURE CUTOFF SWITCH	Switch still open during start - not a running fault	Shutdown	See an authorized Onan dealer
24	COOLANT TEMPERATURE SENDER	Did not sense temperature change during first 5 minutes	Shutdown	See an authorized Onan dealer
25	ENGINE ABOVE SPEED TARGET	Governor unable to regulate to target speed	Shutdown	See an authorized Onan dealer
26	ENGINE BELOW SPEED TARGET	Governor unable to regulate to target speed	Shutdown	Reduce connected load; prime fuel system
27	Voltage Sense	Control unable to sense output voltage	Shutdown	Contact local dealer or distributor
28	DC SENSE LOST	Controller unable to sense DC bus voltage	Shutdown	Open circuit breaker; disconnect excessive loads before starting
29	High Battery Voltage	Voltage across battery system greater than 19 Volts	Shutdown	Check battery bank connections (parallel 12V not series 24V); select lower boost charge rate
31	OVERSPEED	Engine speed greater than 3600 rpm	Shutdown	See an authorized Onan dealer
32	Low Cranking Speed	Cranking speed less than 180 RPM for more than 2 seconds	Shutdown	Clean/tighten battery connections, recharge/replace battery; replace engine oil with proper viscosity
33	HIGH ENGINE COOLANT TEMPERATURE	Engine coolant temperature exceeded design limit	Shutdown	Check coolant level and leaks; remove blockages; reduce load; clean cooling system
34	HIGH INVERTER TEMPERATURE	Inverter heat sink temperature exceeded design limit	Shutdown	Remove blockages from air openings; reduce connected appliances
35	Control Card Failure	Microprocessor EEPROM error during self test	Shutdown	Contact local dealer or distributor
36	Engine Stopped	Engine stopped without receiving command from control	Shutdown	Check fuel level and prime; check air filter; check for mechanical damage
37	INVALID GENSET CONFIGURATION	Genset configuration preprogrammed at factory	Shutdown	See an authorized Onan dealer
38	Over Current (Field Overload)	Low power factor loads	Shutdown	Reduce load; check appliances for proper operation
39	Low Battery Voltage Fault	Battery voltage dropped below 9 volts while genset running; discontinued beginning Spec F	Warning	Clean and tighten battery cable connections; avoid running genset while cranking the vehicle engine where genset batteries supplement vehicle batteries.
41	Generator Rotor	Control unable to sense field or output voltage	Shutdown	Contact local dealer or distributor
42	Processor	Microprocessor ROM error during self test	Shutdown	Contact local dealer or distributor
43	Processor	Microprocessor RAM error during self test	Shutdown	Contact local dealer or distributor
45	Speed Sense	Control unable to sense quadrature frequency	Shutdown	Contact local dealer or distributor
46	INVERTER POWER SUPPLY FAULT	Low battery voltage or power supply device failure	Shutdown	Avoid running genset during vehicle engine cranking; clean battery connections; recharge battery
48	Generator Field Sense	Control unable to sense field voltage	Shutdown	Contact local dealer or distributor
57	Over Prime	Priming exceeded 3 minutes	Shutdown	Check control switch; remove any object holding switch in STOP/PRIME position

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 122-0833.

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

The Cummins/Onan HDKAJ uses fuel filter part number 149-2513.

What air filter fits the Cummins/Onan HDKAJ?

The Cummins/Onan HDKAJ uses air filter part number 140-2897.

Troubleshooting

Fault codes

Code	Meaning	Remedy
1	Engine Over Temperature — during normal operation, the engine coolant temperature exceeded 115 °C (239 °F) for 10 seconds	Check engine coolant level: if coolant level is low, add coolant as necessary and repair any leaks; Check for blockages: if an air inlet or outlet opening on the bottom of the generator set is blocked, remove objects; if dirt is fouling the radiation fins, clean dirt out; Reduce load: reduce the number of connected appliances, especially air conditioners and battery chargers (review load management in Section 4.4)
2	Low Oil Pressure — the low oil pressure cutoff switch did not open	Check engine oil level: if the dipstick indicates oil is low, add oil; if oil is above the full mark on dipstick, drain excess oil
3	Service Check — see second-level fault code
4	Over Crank — cranking exceeded 30 seconds without engine starting	Check fuel level: if fuel level is low, fill the fuel tank; prime the engine fuel system by positioning the control switch to STOP/PRIME for 30 seconds; Check air filter element: replace the air filter if dirty; Replace engine oil with oil of proper viscosity for the ambient temperature; Check fuel fittings: tighten any fuel fitting if there is a fuel or air leak; reprime the engine fuel system by positioning the control switch to STOP/PRIME for 30 seconds; Replace fuel filter
12	Over Voltage — the control is unable to maintain rated voltage	Contact local dealer or distributor
13	Under Voltage — the control is unable to maintain rated voltage	Reduce load: reduce the number of connected appliances, especially air conditioners and battery chargers (review load management in Section 4.4)

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 (37 entries) →

Parts

Part #	Description	Qty	System
122-0833	Filter, Oil	1	Oil filter	Amazon eBay $19.99 NAPA $9.64 FridayParts $20.19
140-2897	Air filter	1	Air filter	Amazon eBay $19.99 FridayParts $48.61
149-2513	Filter, Fuel	1	Fuel filter	Amazon eBay $36.95 NAPA $31.59 FridayParts $48.61
149-2790	Pump, Fuel	1	Pump	Amazon eBay $98.00 FridayParts $24.89
185-5421	Plug, Glow	2	Glow plug	Amazon eBay $35.00
185-5433	Pump Assy, Water	1	Pump	Amazon eBay $35.45 FridayParts $44.80
185-5458	Thermostat	1	Thermostat	Amazon eBay
185-5715	Impeller, Water Pump	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	Auxiliary Fuel Pump Kit		Pump	Amazon eBay
541-0531	Remote Air Cleaner Kit		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 $220.47
FL3325	Filter, Oil (On Engine)	1	Oil filter	Amazon eBay
FL777	Filter, Oil (Skid Mounted)	1	Oil filter	Amazon eBay NAPA $19.46
FS1006	Filter, Fuel Water Separator	2	Fuel filter	Amazon eBay $29.99 NAPA $90.16
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)

This page was generated from the 15 manufacturer documents above by automated extraction; every figure shown is copied from one of them. How the data is compiled.

Cummins/Onan HDKAJ Generator Set

Service parts for the HDKAJ

Air intake

Fuel system

Oil system

Belts

Specifications

Maintenance & consumables

Service intervals

Service specifications

Recommended fluids

Fault codes

Procedures

Common questions

Troubleshooting

Fault codes

Repair guides

Parts

Fuel consumption

Available documents