The Cummins/Onan NH is an engine rated at 1800 rpm, producing up to 5.5 kW. It powers generator sets from Cummins/Onan, including the Contractor.
Also known as: Onan NH
| Rated speed | 1800 rpm |
|---|---|
| Gross power | 5 kW |
How to read your Cummins/Onan engine serial & model number →
| Code | Meaning |
|---|---|
| loss | Loss of coolant |
| Symptom | Cause | Remedy |
|---|---|---|
| Disconnecting Set from RV Systems | 1. First disconnect the negative (-) battery cable from the baitery and then disconnect the battery cables from the genset. 2. Disconnect the remote control wiring harness connector at the genset. 3. Disconnect the generator output wiring and conduit from the power distribution panel or box on the vehicle. Tag all wires to make reconnections easier. 4. Disconnect the exhaust tailpipe from the outlet of the muffler and then remove the muffler. See EXHAUST SYSTEM under Engine Subsystems. 5. Disconnect the fuel line from the genset. Follow the applicable instructions depending on the fuel. | |
| Engine Misfires | Faulty ignition due to: a. worn or fouled spark plugs. **b. worn breaker points. **c. incorrect ignition timing. d. faulty ignition coil, e. faulty plug wires. **f. faulty condenser. **g. faulty ignition module (electronic ignition); Lean fuel mixture due to: a. incorrectly adjusted fuel mixture screws. **b. incorrect float level. c. dirt in carburetor. d. vacuum leak.; Contaminated fuel; Carburetor icing *Gasoline sets only. | A. Replace spark plugs. b. Replace breaker points. c. Set breaker point gap. d. Test coil and replace if necessary. e. Test spark plug wires and f. Replace condenser. g. See Testing Ignition Module.; 2a. Adjust carburetor main and idle adjustment screws. b. Adjust carburetor float level. c. Disassemble carburetor and clean all internal passages. d. Locate leak and correct as required.; 3. Drain fuel tank and refill with fresh fuel. 4. In cold weather, place air preheater in winter position. |
| Engine Backfires | Faulty ignition due to: a. worn or fouled spark plugs. **b. worn breaker points. **c. incorrect ignition timing. d. faulty ignition coil, e. faulty plug wires. **f. faulty condenser. **g. faulty ignition module (electronic ignition) | A. Replace spark plugs. b. Replace breaker points. c. Set breaker point gap. d. Test coil and replace if necessary. e. Test spark plug wires and f. Replace condenser. g. See Testing Ignition Module. |
| Engine Lacks Power | Faulty ignition due to: **a. incorrect ignition timing. b. incorrect spark plug gap. **c. faulty condenser. | A. Adjust breaker point gap. b. Reset spark plug gap. c. Replace condenser. |
| Engine Overheats | Mechanical damage to engine *Gasoline sets only. | See Engine Block Assembly section. |
| Engine Hunts or Surges | 1. Sticking or binding governor linkage. 2. Incorrect governor adjustment 3. Faulty governor spring. 4. Incorrect fuel mixture due to: a. incorrectly adjusted fuel mixture screws, b. incorrect float level, or c. dirt in carburetor. 5. Governor mechanism worn excessively. *6. Carburetor icing. | 1. Clean and lubricate governor linkage. 2. Adjust governor speed and sensitivity. 3. Replace governor spring. 4a. Adjust carburetor main and idle adjustment screws. 4c. Disassemble carburetor and clean all internal passages. |
| High Oil Consumption | 1. Oil viscosity too light or oil is diluted. 2. Crankcase breather valve is dirty or defective. 3. Oil leaks. | 1. Drain oil and refill with correct viscosity oil. 2. Clean crankcase breather and replace if defective. 3. Locate source of leak and repair as required. |
| Low Oil Pressure | 1. Oil viscosity too light or oil is diluted. 2. Low oil level. 3. Low oil pressure switch defective. 4. Faulty oil bypass valve. | 1. Drain oil and refill with correct viscosity oil. 2. Add oil as required. 3. Replace oil pressure switch (see Engine Block Assembly section). 4. Inspect oil bypass valve and clean or replace as required (see Engine Block Assembly section.). |
| Black Exhaust Smoke | Lean fuel mixture due to: a. incorrectly adjusted fuel mixture screws. b. incorrect float level. c. dirt in carburetor. d. vacuum leak. | 3a. Adjust carburetor main and idle adjustment screws. 1b. Adjust carburetor float level. 1c. Disassemble carburetor and clean all internal passages. 1 Replace fuel filter. 4d. Repair vacuum leak. |
| White or Blue Exhaust Smoke | Rich fuel mixture due to: a. incorrect float level b. faulty carburetor float. | 1a. Adjust carburetor float level. 1b. Replace faulty carburetor float. |
| Engine surges | 1. Sticking or binding (mechanical) governor linkage. 2. Incorrect (mechanical) governor adjustment. 3. Faulty (mechanical) governor spring. 4. Incorrect fuel mixture due to: a. incorrectly adjusted fuel mixture screws.1 b. incorrect float level.1. 2 c. dirt in carburetor d. ignition misfires 5. Intermittent electrical connections. 6. Governor mechanism worn excessively. 7. Fuel supply problem caused by: a. Faulty fuel pump.2 b. Contaminated fuel supply.2 c. Vapor locking.2 d. Plugged fuel filter | 1. Clean governor linkage (remove dirt or ice buildup). Check that linkage does not touch other parts. 2. Adjust governor speed and sensitivity. 3. Replace governor spring. 4a. Adjust carburetor main and idle adjustment screws.1 4b. Adjust carburetor float level.1 4c. Disassemble carburetor and clean all internal passages.1 4d. Check connections, see Ignition section. 5. Check battery and ignition connections. 6. See Engine Block Assembly section.. 7a. Check fuel pump and replace if defective. 7b. Drain and refill fuel supply 7c. Check for cause of overheating 7d. Replace fuel filter. |
| Make sure there is ample fresh air when operating the genset in a confined area. | Ensure adequate ventilation when operating the genset in a confined space. | |
| Overheats | Restricted airflow due to: a.debris blocking air inlet or outlet. | Clear away debris. Do not use genset compartment for storage. |
| Lean fuel mixture | A.incorrectly adjusted fuel mixture screws. | Adjust carburetor main and idle adjustment screws.1 |
| Contaminated fuel supply | 2.Contaminated fuel.2 | Drain and replace fuel. |
| Governor mechanism worn excessively | 6.Governor mechanism worn excessively. | See Engine Block Assembly section. |
| Sticking or binding (mechanical) governor linkage | 1.Clean governor linkage (remove dirt or ice buildup). Check that linkage does not touch other parts. | |
| Incorrect (mechanical) governor adjustment | 2.Incorrect (mechanical) governor adjustment. | Adjust governor speed and sensitivity. |
| Faulty (mechanical) governor spring | 3.Faulty (mechanical) governor spring. | Replace governor spring. |
| Incorrect fuel mixture | 4a. Adjust carburetor main and idle adjustment screws. | Adjust carburetor main and idle adjustment screws.1 |
| Intermittent electrical connections | 5.Intermittent electrical connections. | Check battery and ignition connections. |
| Fuel supply problem caused by: a.Faulty fuel pump. | Check fuel pump and replace if defective. | |
| Fuel supply problem caused by: b.Contaminated fuel supply. | Drain and refill fuel supply | |
| Fuel supply problem caused by: c. Vapor locking. | Check for cause of overheating | |
| Fuel supply problem caused by: d.Plugged fuel filter. | Replace fuel filter. | |
| Carburetor icing | 8.Carburetor icing.2 | In cold weather, place air preheater in winter position. |
| Faulty ignition due to: a. worn or fouled spark plugs. | Misfires | Replace spark plugs. |
| Faulty ignition due to: b. faulty ignition coil. | Misfires | Test coil and replace if necessary. |
| Faulty ignition due to: c. faulty plug wires. | Misfires | Test spark plug wires and replace if faulty. |
| Lean fuel mixture due to: a. incorrectly adjusted main and idle adjustment screws. | Adjust carburetor main and idle adjustment screws. | |
| Lean fuel mixture due to: b. incorrect float level. | Adjust carburetor float level. | |
| Lean fuel mixture due to: c. dirt in carburetor. | Disassemble carburetor and clean all internal passages. Replace fuel filter. | |
| Lean fuel mixture due to: d. vacuum leak. | Locate leak and correct as required. | |
| Lean fuel mixture due to: e. altitude setting. | Reset altitude adjust knob on carburetor. | |
| Contaminated fuel. | Drain fuel tank and refill with fresh fuel. | |
| Carburetor icing. | Place air preheater in winter position. | |
| Faulty ignition due to incorrect spark plug gap. | Reset spark plug gap. | |
| Dirty air cleaner. | Replace air cleaner. | |
| Restricted fuel flow due to: a. Plugged fuel filter. | Replace fuel filter. | |
| Dizziness | IF YOU OR ANYONE ELSE EXPERIENCE ANY OF THESE SYMPTOMS, GET OUT INTO THE FRESH AIR IMMEDIATELY. If symptoms persist, seek medical attention. Shut down the unit and do not operate until it has been inspected and repaired. | |
| Muscular Twitching | IF YOU OR ANYONE ELSE EXPERIENCE ANY OF THESE SYMPTOMS, GET OUT INTO THE FRESH AIR IMMEDIATELY. If symptoms persist, seek medical attention. Shut down the unit and do not operate until it has been inspected and repaired. | |
| Vomiting | IF YOU OR ANYONE ELSE EXPERIENCE ANY OF THESE SYMPTOMS, GET OUT INTO THE FRESH AIR IMMEDIATELY. If symptoms persist, seek medical attention. Shut down the unit and do not operate until it has been inspected and repaired. | |
| Weakness and Sleepiness | IF YOU OR ANYONE ELSE EXPERIENCE ANY OF THESE SYMPTOMS, GET OUT INTO THE FRESH AIR IMMEDIATELY. If symptoms persist, seek medical attention. Shut down the unit and do not operate until it has been inspected and repaired. | |
| Inability to Think Coherently | IF YOU OR ANYONE ELSE EXPERIENCE ANY OF THESE SYMPTOMS, GET OUT INTO THE FRESH AIR IMMEDIATELY. If symptoms persist, seek medical attention. Shut down the unit and do not operate until it has been inspected and repaired. | |
| FAILS TO CRANK | 1. Low battery 2. Bad battery connection 3. Blown fuse. | |
| CRANKS SLOWLY | 1. Low battery. | 1. Check battery electrolyte level. 2. Clean and tighten all battery and cable connections. |
| CRANKS BUT WON'T START | Faulty Fuel Solenoid or Plugged Fuel Filter, Faulty Ignition | Fuel solenoid must open during cranking and running. Check by cranking set with spark plugs disconnected. Push priming button on regulator and listen for fuel flow and propane odor. If no flow or odor, check and replace fuel filter or fuel solenoid valve., Check to see if points open and close during cranking. If they do not open and close, adjust and set points. Plug and plug wires must be in good condition. Voltage at ignition coil negative terminal (-) must alternate from +12 volts to zero as points open and close during engine cranking., Check voltage from relay terminal '4' to ground while cranking unit. Battery voltage should appear at this terminal. If not check |
| CRANKS BUT WON’T START | 1. Fuel below genset pick-up level 2. Fuel supply shutoff valve closed. 3. Carbon deposits on spark plugs. 4. Blown fuel pump/in tank. | 1. Add fuel. 2. Fully open fuel supply valve. 3. Remove spark plugs and clean. 4. Replace fuse with same type and rating. If problem persists, see Onan service center. |
| EXHAUSTING BLACK SMOKE | 1. Rich fuel mixture. 2. Dirty air filter. 3. Choke stuck. | 1. Turn main fuel adjustment in 1/8 turn (location of adjustment is shown in Figure 3-1). 2. Replace air filter. 3. Contact an Onan service center. |
| UNIT RUNS THEN STOPS | 1. Out of fuel. 2. Low oil level. 3. Excess oil. | 1. Refill fuel tank. 2. Add oil if necessary. 3. Reduce engine oil level. |
| UNIT RUNS BUT SURGES | 1. Loose or worn spark plug leads at spark plugs and ignition coil. 2. Ignition coil, wiring, or control components defective. 3. Faulty spark plugs. 4. Governor out of adjustment. | 1. Check security of spark plug leads at spark plugs and ignition coil. Replace leads if worn. 2. Contact an Onan representative. 3. Remove and clean or replace faulty spark plugs. 4. Contact an Onan service center. |
| Low Bat LED (red) MAY flash ON | If it stays on during operation, see BATTERY CARE under Periodic Maintenance. | |
| Engine does not crank or start after several tries or stops running. | See Troubleshooting if the engine does not crank or start after several tries or stops running. | |
| The engine fails to crank at the remote START switch. | A. Turn the enable switch (if so equipped) to the enable position. b. Try starting at the genset rather than at the remote control. c. Push the genset control panel switch to RESET and then to START. | |
| The engine fails to crank at the genset START switch and Start Sol (Fig. 3) does not light. | A. Turn the enable switch (if so equipped) to the enable position. b. Push the genset control panel switch to RESET and then to START. c. Replace fuse F1 on the side of the control box if it has blown. d. Clean and tighten the positive (+) and negative (- ) battery cable connections at the battery and the genset. e. Recharge the battery. Refer to the battery manufacturer’s recommendations. | |
| The engine fails to crank at the genset START switch but Start Sol (Fig. 3) does light. | A. Clean and tighten the positive (+) and negative (- ) battery cable connections at the battery and the genset. b. Recharge the battery. Refer to the battery manufacturer’s recommendations. | |
| The engine cranks slowly. | A. Disconnect large electrical and mechanical loads. b. Clean and tighten the positive (+) and negative (- ) battery cable connections at the battery and the genset. c. Recharge the battery. Refer to the battery manufacturer’s recommendations. d. Change the engine oil to oil having the proper viscosity for the ambient temperature. See Table 1 on Page 3. | |
| The engine cranks but fails to start. Fuel Pump, AVR Field and Ignition (Fig. 3) do light. | A. Check the fuel tank and fill if necessary. b. Open any closed fuel shut off valve. c. Check engine oil level and add oil as necessary. d. Service the air cleaner. e. Secure the spark plug leads on the spark plugs. f. Replace the spark plugs. | |
| The engine cranks but fails to start. Fuel Pump, AVR Field or Ignition (Fig. 3) does not light. | Contact an authorized Onan dealer. | |
| The engine runs and then stops or surges. | A. Check the fuel tank and fill if necessary. b. Check the engine oil level and add oil as necessary. Drain excess oil if the level is above the dipstick Full mark. c. Check and reset the carburetor preheater lever and altitude adjust knob (gasoline models only). See Varying Weather and Altitude. d. Secure the spark plug leads on the spark plugs. e. Replace the spark plugs. | |
| The genset keeps stalling or the circuit breaker keeps tripping. | A. Try running with fewer appliances connected. See Powering Equipment. b. Check the fuel tank (LPG, vapor-withdrawal models) and fill as necessary. On cold days the LPG container may have to be kept at least half full to provide the rate of vaporization necessary to keep up with the genset fuel demand. | |
| There is no electrical power even though the genset runs and Gen AC (Fig. 3) lights. | A. Reset tripped circuit breakers. See Powering Equipment. b. Unless there is an automatic power transfer switch, plug the vehicle power cord into the genset power output receptacle (if so equipped) or turn the vehicle power selector switch to its genset position (if so equipped). | |
| Low Bat (Fig. 3) lights and/or the remote battery meter (Fig. 4) indicates low voltage. | A. Clean and tighten the positive (+) and negative (- ) battery cable connections at the battery and the genset. b. Recharge the battery. Refer to the battery manufacturer’s recommendations. | |
| Black smoke exits the tailpipe. | Service the air cleaner. | |
| The engine fails to crank. | A. Try starting at the genset rather than at the remote control. b. Replace fuse F1 on the control panel if it has blown. c. Clean and tighten the positive (+) and negative (- ) battery cable connections at the battery and the genset. d. Recharge the battery. Refer to the battery manufacturer’s recommendations. | |
| The engine cranks but fails to start. | A. Check the fuel tank and fill if necessary. b. Open any closed fuel shut off valve. c. Check engine oil level and add oil as necessary. d. Replace fuse F2 (side of control panel) if it has blown. e. Service the air cleaner. f. Secure the spark plug leads on the spark plugs. g. Replace the spark plugs. | |
| There is no electrical power even though the genset runs. | A. Reset tripped circuit breakers. See Powering Equipment. b. Unless there is an automatic power transfer switch, plug the vehicle power cord into the genset power output receptacle (if so equipped) or turn the vehicle power selector switch to its genset position (if so equipped). | |
| The remote battery condition meter indicates low voltage. | A. Clean and tighten the positive (+) and negative (- ) battery cable connections at the battery and the genset. b. Recharge the battery. Refer to the battery manufacturer’s recommendations. | |
| Eng Cranks But Will Not Start (Genset) | -01 Check: - Spark plugs - Ignition coil - Ignition module -02 Perform checks in step 01 | |
| Engine Overfueling (Genset) | -01 Check: - Spark plugs - Fuel pressure at carburetor - Vacuum pull−off - Electric choke heater -02 Perform checks in step 01 - Check: - Governor adjustments - Carburetor adjustments -03 Perform checks in step 02 - Check: - Ignition coil - Ignition module | |
| Engine Unstable (Hunts) (Genset) | -01 Check: - Fuel supply - Fuel Lines for leakage - Loose wire connection -02 Perform checks in step 01 - Check: - Governor linkage for binding - Governor adjustments - Carburetor adjustments | |
| Engine Will Not Crank (Genset) | -01 Check: - Low battery voltage - Terminal connection−loose or dirty - Battery cable size - Starter drive engagement -02 Perform checks in step 01 - Check: - Remote control - Connections on PCB control board - Start solenoid - Starter | |
| High/Low AC Output (Genset) | -01 Check: - Broken or loose wires - Voltage regulator - Transformer regulator - Engine speed - Voltage ad | |
| Blue Exhaust Smoke | 1. Incorrect float level in carburetor. | Adjust carburetor float level. Replace carburetor float |
| High Oil Consumption (Note: New engines sometimes have high oil consumption during break-In) | 1. Oil viscosity too light or oil is diluted. 2. Crankcase breather valve is dirty or faulty. 3. Oil leaks. 4. Excessive engine wear. 5. Light loading. | |
| If the genset fails to start | See the Troubleshooting Guide in the Operator’s Manual | |
| Fuel leaks are found | Stop the set immediately, close off the fuel supply and have the leak(s) repaired | |
| Exhaust system for leaks is examined | Stop the set and have the exhaust system repaired immediately | |
| Generator set is excessively noisy | Have it inspected and repaired immediately by an authorized Onan service center |
Fault codes and symptom→remedy steps extracted from this engine’s service/owner documentation; verify against the official manual before servicing.
| Item | Spec | Capacity | Part # | Interval | |
|---|---|---|---|---|---|
| Air filter | — | 100 hr | |||
| Fuel filter | — | 400 hr | |||
| Oil filter | — | 200 hr | |||
| Battery | — | 30 hr | |||
| Belt | — | ||||
| Coolant | — | ||||
| Coolant filter | — | ||||
| Oil | 3.3 L | — | 25 hr | ||
| Spark plug | — | 100 hr |
Pooled from every document that names this exact engine — confirm the interval and part number against your unit's serial number.
Step-by-step procedures compiled from the Cummins/Onan service manual for this engine.
The Cummins/Onan NH powers 1 generator set(s), including Cummins/Onan Contractor.
The Cummins/Onan NH oil change interval is every 25 hours.