Cummins/Onan NTA-855-G2 troubleshooting: 19 fault codes and symptom-cause-remedy entries from the manufacturer's own service documentation.
Cummins/Onan NTA-855-G2 — full specs, parts & maintenance.
All Cummins/Onan fault codes →
| Symptom | Cause | Remedy |
|---|---|---|
| Engine will not crank. | Possible fault with control or starting system. | A. Fault lamp on. Correct fault and reset control. b. Poor battery cable connections. Clean the battery cable terminals and tighten all connections. c. Discharged or defective battery. Recharge or replace the battery. d. Contact your distributor for assistance if none of the above applies. |
| Engine starts from Manual Start controls but will not start automatically or from a remote panel. | Automatic Start switch must be in Auto position for automatic or remote starting. | 2. Aremote circuit breaker is tripped, reset breaker and restart. Contact your distributor if breaker trips after resetting. Remote wiring connections are incorrect. Review all remote start wiring, correct as needed. |
| No AC output voltage. | 3. Confirm that Exciter Switch is at ON position. Voltage regulator is inoperative. Refer to Initial Start and Checks, and Adjustments sections for voltage check and adjustment procedures. Contact your distributor if voltage build-up is still a problem. | |
| Engine runs and then shuts down, OVERSPEED lamp lights. | 4. Indicates engine has exceeded normal operating speed. Contact your distributor for service. | |
| LO OIL PRES lamp lights. Engine shuts down. | Engine oil pressure has dropped to 12 psi (88 kPa). | 5. Check oil level, lines and filters. If oil system is okay but oil level is low, replenish. Reset control and restart. Contact your distributor if oil pressure is not in the range of 40 to 70 psi (276 to 483 kPa). |
| H1 ENG COOLANT TEMP lamp lights. Engine shuts down. | Engine has overheated or coolant level is low (sets with coolant level sensor). | 6. Allow engine to cool down completely before proceeding with the following checks: a. Check coolant level and replenish if low. Look for possible coolant leakage points and repair if necessary. b. Check for obstructions to cooling airflow and correct as necessary. c. Check for a slipping fan belt, tighten if loose. d. Reset control and restart after locating and correcting problem. Contact your distributor if none of the above applies. |
| REMOTE STOP lamp lights. | 7. This fault function is programmed to shut down the set immediately, as in the case of an Emergency Stop pushbutton. The nature and location of the fault is an optional selection that is determined when the set installation is designed. Refer to specifics of on-site equipment. | |
| PRE LO OIL PRES lamp lights. | 8. Indicates engine oil pressure has dropped to 18 psi (124 kPa). If generator is powering critical loads and cannot be shut down, wait until next shutdown period and then follow step 5 procedure. If engine can be stopped, follow procedure in step 5. | |
| Sensor operation and allow the engine to overheat causing severe damage to the engine | Loss of coolant | Maintain adequate coolant level so the high engine coolant temperature Shutdown system can function properly. |
| Engine shutdown and lighting of high engine coolant temperature fault lamp | Low Coolant Level | A fluid level sensing switch provides engine shutdown if coolant level falls too low. |
| Engine continues to operate. Engine coolant temperature has risen to approximately 215°F (102°C). | A. Reduce load if possible by turning off non-Critical loads. b. Check air inlets and outlets and remove any obstructions to airflow. c. Open doors or windows in generator area to increase ventilation. | |
| LO ENG TEMP lamp lights. | A. Coolant heater not connected to power supply. Check for blown fuse or disconnected heater cord and correct as required. b. Check for low coolant level and replenish if required. Look for possible coolant leakage points and repair as required. c. Contact your distributor if none of the above applies. | |
| CONTROL NOT IN AUTO lamp flashes. | Moving the Automatic Start switch to the AUTO position will stop the lamp flashing and enable automatic starting. | |
| Engine cranks but will not start. OVERCRANK lamp lights and engine stops cranking. | A. Check for empty fuel tank, fuel leaks, or plugged fuel lines and correct as required. b. Check for dirty fuel filter and replace if necessary (see Maintenance section.) c. Also check for fuel shutoff valves not open, and leaks into suction line, etc. d. Check for dirty or plugged air filter and replace if necessary (see Maintenance section.) e. Refer to step 5. Reset the control and restart after correcting the problem. Contact your distributor for service if none of the above applies. | |
| LO FUEL lamp lights. Engine continues to run. | Check fuel supply and replenish as required. | |
| LO FUEL lamp lights. Engine shuts down and LO OIL PRES lamp lights. | Check fuel level and replenish as required. | |
| LOW BATTERY VOLTAGE lamp lights. | A. Poor battery cable connections. Clean the battery cable terminals and tighten all connections. b. Discharged or defective battery. Recharge or replace the battery. | |
| BATTERY CHARGER FAILURE lamp lights. | Refer to battery charger unit and remedy condition. | |
| Set-mounted circuit breaker tripped. | The optional line circuit breaker mounts on the generator conduit box. If the load exceeds the circuit breaker current rating, the circuit breaker will open to prevent the generator from being overloaded. If the circuit breaker trips, locate the source of the overload and correct as required. Manually reset the breaker to reconnect the load to the generator. Optional shunt trip functions can cause the generator set to shut down and will require resetting the control. |
Fault codes and symptom→remedy steps extracted from this model’s service/owner documentation; verify against the official manual before servicing.
Documented causes: Possible fault with control or starting system.. See the table for the matching fixes.
Documented causes: Automatic Start switch must be in Auto position for automatic or remote starting.. See the table for the matching fixes.
Documented causes: Engine oil pressure has dropped to 12 psi (88 kPa).. See the table for the matching fixes.