Cummins/Onan 300 DFCB troubleshooting: 2 fault codes and 19 symptom-cause-remedy entries from the manufacturer's own service documentation.
Cummins/Onan 300 DFCB — full specs, parts & maintenance.
All Cummins/Onan fault codes →
| Code | Meaning | Cause |
|---|---|---|
| FAULT 1 | The FAULT 1 or FAULT 2 fault lamp lights. Engine shuts down immediately, engine runs for several seconds and then shuts down, or engine continues to run. | The standard undesignated fault functions are programmed to shut down the set when a fault is sensed. Fault 1 is time delayed while Fault 2 is immediate. The nature of the fault is an optional selection that is determined when the set installation is designed. The undesignated fault functions may also be programmed for non-shutdown or non-time delay. |
| FAULT 2 | The FAULT 1 or FAULT 2 fault lamp lights. Engine shuts down immediately, engine runs for several seconds and then shuts down, or engine continues to run. | The standard undesignated fault functions are programmed to shut down the set when a fault is sensed. Fault 1 is time delayed while Fault 2 is immediate. The nature of the fault is an optional selection that is determined when the set installation is designed. The undesignated fault functions may also be programmed for non-shutdown or non-time delay. |
| Symptom | Cause | Remedy |
|---|---|---|
| PRE HI ENGINE TEMP lamp lights. Engine continues to operate. | Engine has begun to overheat and engine temperature has risen to approximately 215°F (102°C). | If generator is powering non-critical and critical loads and cannot be shut down: reduce load if possible by turning off non-critical loads; check air inlets and outlets and remove any obstructions to airflow. If engine can be stopped, follow procedure in step 3. |
| HI ENG TEMP lamp lights. Engine shuts down. | Engine has overheated (engine temperature has risen above 222°F/106°C) or coolant level is low (sets with coolant level sensor). | Allow engine to cool down completely before proceeding: check coolant level and replenish if low, look for possible coolant leakage points and repair if necessary; check for obstructions to cooling airflow and correct as necessary; check for a slipping fan belt and tighten if loose; reset control and restart after locating and correcting problem; contact an authorized service center if none of the above. |
| PRE LO OIL PRES lamp lights. Engine continues to operate. | Engine oil pressure has dropped to 20 psi (138 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 procedures in step 5. |
| LO OIL PRES lamp lights. Engine shuts down. | Engine oil pressure has dropped to 14 psi (97 kPa). | Check oil level, lines and filters; if oil system is OK but oil level is low, replenish; reset control and restart; contact an authorized service center if oil pressure is not in the range of 25 to 40 psi (172 to 275 kPa). |
| OVERCRANK lamp lights and engine stops cranking. or Engine runs, shuts down, and LO OIL PRES lamp lights. | Possible fuel system problem. | Check for empty fuel tank, fuel leaks, or plugged fuel lines and correct as required; check for dirty fuel filter and replace if necessary (see Maintenance section); check for dirty or plugged air filter and replace if necessary (see Maintenance section); reset the control and restart after correcting the problem; contact an authorized service center for service if none of the above. |
| Engine runs and then shuts down, OVERSPEED lamp lights. | Engine has exceeded normal operating speed. | Contact an authorized service center for service. |
| SWITCH OFF lamp flashes. | Run/Stop/Remote switch is in the Stop position which will prevent automatic starting if an automatic transfer switch is used. | Move the Run/Stop/Remote switch to the Remote position for automatic starting. |
| LO FUEL lamp lights. Engine continues to run. | Diesel fuel supply is running low. | Check fuel supply and replenish as required. |
| LO FUEL LAMP lights. Engine shuts down and LO OIL PRES lamp lights. | Engine has run out of fuel. | Check fuel level and replenish as required. |
| LO ENG TEMP lamp lights. Set is in standby mode but is not operating. (Lamp lights when engine coolant temperature is 70°F (21°C) or lower. Since the lamp goes out after the engine warms up, there should be no cause for alarm even during initial generator set operation.) | Engine coolant heater is not operating or is not circulating coolant. | Check for the following conditions: coolant heater not connected to power supply, check for blown fuse or disconnected heater cord and correct as required; check for low coolant level and replenish if required, look for possible coolant leakage points and repair as required; contact an authorized service center if none of the above. |
| Fault lamp lights but no fault exists. Engine gauges show oil pressure, engine temperature, and frequency (speed) are within normal limits. | The monitor board or a sensor may be at fault. | Contact an authorized service center for service. |
| Engine starts from generator control panel but will not start automatically or from a remote panel. (Note: The Run/Stop/Remote switch must be in the Remote position for automatic or remote starting). | Remote circuit breaker is tripped. | Reset breaker and restart; contact an authorized service center if breaker trips after resetting. |
| Engine will not crank. | Fault lamp on. | Correct fault and reset control. |
| Engine will not crank. | Poor battery cable connections. | Clean the battery cable terminals and tighten all connections. |
| Engine will not crank. | Discharged or defective battery. | Recharge or replace the battery. |
| Engine will not crank. | Emergency stop button (if equipped) pushed in. | To reset, pull switch out and move Run/Stop/Remote switch to Stop position. Then push test switch to Reset/Lamp position. |
| Engine will not crank. | Possible fault with control or starting system (none of the above). | Contact an authorized service center if none of the above. |
| No AC output voltage. | Field breaker is tripped. | Reset breaker; contact an authorized service center if voltage buildup causes breaker to trip. |
| Green RUN lamp does not light following engine startup. | Possible Start/Disconnect relay failure. | Contact an authorized service center for assistance. |
Fault codes and symptom→remedy steps extracted from this model’s service/owner documentation; verify against the official manual before servicing.
Documented causes: Fault lamp on.; Poor battery cable connections.; Discharged or defective battery.; Emergency stop button (if equipped) pushed in.. See the table for the matching fixes.
Documented causes: The standard undesignated fault functions are programmed to shut down the set when a fault is sensed. Fault 1 is time delayed while Fault 2 is immediate. The nature of the fault is an optional selection that is determined when the set installation is designed. The undesignated fault functions may also be programmed for non-shutdown or non-time delay.. See the table for the matching fixes.
Documented causes: Engine has begun to overheat and engine temperature has risen to approximately 215°F (102°C).. See the table for the matching fixes.