Onan is the name of a comprehensive line of generator sets produced by the Cummins Power Generation company. In its turn, it belongs to Cummins Inc., which designs, manufactures, and sells diesel and natural gas engines and a wide range of related products, form filtration solutions to electrical power generation systems.
Although Onan generators are comparatively reliable, it doesn’t mean they can’t break at times. The tables below offer several troubleshooting possibilities. Everything depends on the type of problem your appliance is experiencing. Find the symptom you’ve noticed in the table below to solve the issue.
| PROBLEM | PROBABLE CAUSE | REMEDY |
|---|---|---|
| FAILS TO CRANK | 1. Bad Battery Connection | 1. Clean and tighten all battery and cable connections |
| 2. Low Battery | 2. A Check specific gravity. Recharge or replace battery if necessary. | |
| 2. B Reverse current doted (CR1) may be shorted or open causing a drain on the battery R2 may be open. | ||
| 3. Faulty Start Solenoid (K1) | 3. Push start switch. Check star* solenoid "S1” terminal voltage to ground When battery voltage at start solenoid "B + " terminal is present, battery voltage should also appear at “Si" terminal: if not. replace start solenoid. | |
| 4. Faulty Start Switch | 4. Jumper switch (#3 terminal) to ground. If solenoid energizes, replace switch. | |
| CRANKS SLOWLY | 1. Bad Battery Connection | |
| 2. Low Battery | ||
| CRANKS BUT WONT START | 1. Blown Fuse (F2) | 1. Replace fuse (F2) on control. |
| 2. Faulty Fuel Solenoid Or Fuel Pump. On later models, fuel solenoid is an integral part of fuel pump. | 2. Fuel solenoid must open during cranking and running. Check by removing steel line from carburetor and crank engine. If fuel solenoid is open, fuel will pulsate out of this line. If it does not, the fuel solenoid and fuel pump must be checked separately to determine defective part. | |
| 3. Faulty Ignition | 3. 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 volts as points open and close during engine cranking. | |
| 4. Inoperative Choke | 4. With engine not running, check choke vane movement by pushing choke lever arm. Choke must be in closed position with cold engine, and must be free to move against bimetal spring As engine warms up, bi-metal spring relaxes and allows choke vane to open fully. The lever will pulsate as engine warms up See ADJUSTMENT section. | |
| 5. Faulty Crank Ignition Relay (K2) | 5. Check voltage from relay terminal ”4,‘ to ground while cranking unit. Battery voltage should appear at this terminal. If not check for voltage at relay terminals "1" and "2”. If battery voltage is present at terminals 1 and 2. but not at 4. replace relay. If not voltage appears at terminals 1 and 2 on relay while cranking, check wiring between start solenoid (K1) and crank ignition relay (K2). | |
| UNIT STARTS, BUT STOPS IMMEDIATELY AFTER RELEASING START SWITCH S1 | 1. Resistor Rl may be open. | 1. Check voltage on both sides of Rl With set running voltage should be 24-32 volts DC |
| 2. Run Ignition Relay K3 | 2. Check voltage on both sides of K3. Should be 12 volts | |
| 3. Low Oil Level | 3. Check oil level. If low or empty, refill to proper level | |
| 4. Low oil pressure switch may be defective. | 4. Check S3. Switch should close with set running at 10 lbs minimum oil pressure. | |
| UNITS RUNS THEN STOPS | 1. Low Oil Level | 1. Check oil level. If low or empty, refill to proper level. |
| UNITS RUNS BUT SUHGES | 1. Stuck Choke | |
| 2 Governor Not Adjusted Properly | 2. Readjust governor. | |
| UNITS STOPS | 1. Faulty Ignition | |
| 2. Out of Fuel | 2. Refill fuel tank. | |
| 3. Low Oil Level | 3. Check oil level. If low or empty, refill to proper level. | |
| REMOTE RUNNING TIME METER OR GENERATOR LAMP INOPERATIVE | 1. Blown Fuse (F1) | 1. Replace F1 fuse on control. |
| Problem | Corrective Action |
|---|---|
| 1. 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. | |
| 2. The engine cranks slowly. | a. Disconnect the air conditioner and other large loads. |
| b. Clean and tighten the positive (+) and negative (-) battery cable connections at the battery and the genset. | |
| c. Recharge the battery. | |
| d. Change the engine oil to oil having the proper viscosity for the ambient temperature. | |
| 3. 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 (gasoline only). | |
| e. Service the air cleaner. | |
| f. Secure the spark plug leads on the spark plugs. | |
| g. Replace the spark plugs. | |
| 4. 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. | |
| d. Secure the spark plug leads on the spark plugs. | |
| e. Replace the spark plugs. | |
| 5. The genset keeps stalling or the circuit breaker keeps tripping. | a. Try running with fewer appliances connected. |
| 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. | |
| 6. There is no electrical power even though the genset runs. | a. Reset tripped circuit breakers. |
| 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). | |
| 7. The remote battery condition 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. | |
| 8. Black smoke exits the tailpape | Service the air cleaner. |
| Possible Cause | Corrective Action |
|---|---|
| 1. Air trapped in hydraulic fluid | Purge the air and refill the oil reservoir as necessary. A caution! Running the pump without oil will quickly destroy the pump. |
| 1. Loose fan, worn bearing or misaligned rotor and motor | |
| 1. ON/OFF Switch OFF | Turn the switch ON. |
| 2. ON/OFF Switch was ON when the engine was started or the PTO was engaged | Turn the switch OFF and then ON. |
| 3. Disengaged PTO | Engage the PTO. |
| 4. Blown Fuse (F1) | Replace with a 20 amp (yellow) blade-type fuse. If the new fuse blows, check for ground faults in harnesses 338-4084, 338-4085 and 338-4087 and replace as necessary. |
| 5. Blown Fuse (F2) | Replace with a 0.125 amp slow-blow fuse. |
| 6. Hydraulic fluid leak | Check for and repair any leaks in the system and refill as necessary |
| 7. 12 VDC not available or polarity reversed. | Disconnect connector J1 at the genset and check for 12 VDC across pins A and B and Positive (+) 12 VDC at pin A. |
| 8. Faulty ON/OFF Switch | Disconnect connector P2 at the genset and check for electrical continuity across pins A and B when the switch is turned on. |
| 9. Faulty Lead Harness | Check for bent, corroded or missing connector pins and damaged leads in harnesses 338-4084, 338-4085 and 338-4086 and replace as necessary. |
| 1. Line circuit breaker (vehicle AC distribution panel) OFF, TRIPPED or faulty | a. If the circuit breaker is OFF, find out why, make sure it is safe to reconnect power, and then switch it ON. |
| b. If the circuit breaker TRIPPED, shut down the genset and repair the shorted or grounded equipment that caused tripping. | |
| c. Replace a faulty circuit breaker. | |
| 2. Misconnected Genset Power Supply Conductors | Reconnect the genset power supply conductors correctly at the vehicle AC distribution panel |
| 3. Wrong PTO speed ratio or faulty hydraulic motor or controller | a. Verify that the combination of PTO speed ratio and engine speed range results in pump speeds that fall within the specified range If pump speed falls outside the range, reinstall the PTO with a gear ratio that will keep pump speed within the specified range at all engine speeds. |
| 1. Wrong PTO speed ratio or faulty hydraulic motor or controller | a. Voltage is frequency dependent. Verify that the combination of PTO speed ratio and engine speed range results in pump speeds that fall within the specified range. If pump speed falls outside the range, reinstall the PTO with a gear ratio that will keep pump speed within the specified range at all engine speeds. |