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 |
| Code | Meaning |
|---|---|
| loss | Loss of coolant |
| Symptom | Cause | Remedy |
|---|---|---|
| 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.). |
| FAILS TO CRANK | Bad Battery Connection, Low Battery, Reverse current diode (CR1) may be shorted or open causing a drain on the battery. R2 may be open, Faulty Start Solenoid (K1), Faulty Start Switch | Clean and tighten all battery and cable connections., Check specific gravity. Recharge or replace battery if necessary., Push start switch. Check start solenoid 'S1' terminal voltage to ground When battery voltage at start solenoid 'B+' terminal is present. battery voltage should also appear at 'Sl' terminal; ii not. replace start solenoid., Jumper switch (#3 terminal) to ground. If solenoid energizes, replace switch. |
| CRANKS SLOWLY | Bad Battery Connection, Low Battery | Replace fuse (F2) |
| 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 |
| 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. | |
| Black Exhaust Smoke | Dirty air cleaner. Restricted fuel flow due to: a. plugged fuel filter or b. faulty fuel pump. Incorrect fuel mixture due to: a. incorrectly adjusted | A. Clean air cleaner. b. Replace or clean fuel filter if necessary. c. Repair or replace fuel pump as required. d. Adjust carburetor main and idle adjustment screws. |
Fault codes and symptom→remedy steps extracted from this engine’s service/owner documentation; verify against the official manual before servicing.
The Cummins/Onan NH powers 1 generator set(s), including Cummins/Onan Contractor.