Cummins/Onan ES-1788 troubleshooting: 18 fault codes and symptom-cause-remedy entries from the manufacturer's own service documentation.
Cummins/Onan ES-1788 — full specs, parts & maintenance.
All Cummins/Onan fault codes →
| Symptom | Cause | Remedy |
|---|---|---|
| Green RUN lamp lights following engine start-up. | Indicates all engine systems are normal. No corrective action required. | |
| PRE Hi ENGINE TEMP lamp lights. Engine continues to operate. | Indicates engine has begun to overheat and engine temperature has risen to approximately 202°F (94°C). If generator is powering non-critical and critical loads and cannot be shutdown, use the following: 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. If engine can be stopped, follow procedure in step 3. | |
| HI ENG TEMP lamp lights. Engine shuts down. | Indicates 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 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 and tighten if loose. d. Reset control and restart after locating and correcting problem. Contact a Cummins Dealer or Distributor if none of the above. | |
| PRE LO OIL PRES lamp lights. Engine continues to operate. | Indicates 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. | Indicates engine oil pressure has dropped to 14 psi (97 kPa). Check oil level, lines and filters. If oil system is okay but oil level is low, replenish. Reset control and restart. Contact a Cummins Dealer or Distributor if oil pressure is not in the range of 35 to 55 psi (241 to 379 kPa). | |
| OVERCRANK lamp lights and engine stops cranking. | Indicates possible fuel system problem. 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. Check for dirty or plugged air filter and replace if necessary (see Maintenance section). d. Refer to Step 5. e. Reset the control and restart after correcting the problem. Contact a Cummins Dealer for service if none of the above. | |
| Engine runs, shuts down, and LO OIL PRES lamp lights. | Indicates engine has exceeded normal operating speed. Contact a Cummins Dealer for service. | |
| SWITCH OFF lamp flashes. | Indicates 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. | Indicates 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. | Indicates 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. Indicates engine coolant heater is not operating or is not circulating coolant. Check for the following conditions: 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 a Cummins Dealer if none of the above. | |
| Engine does not start | Place the Run/Stop/Remote switch in the STOP position and momentarily depress the Reset switch. Wait two minutes for the starter motor to cool and then repeat the starting procedure. | |
| Engine does not run after a second attempt at starting | Refer to the Troubleshooting section | |
| Fault lamp lights but no fault exists. | The monitor board or a sensor may be at fault. | Contact a Cummins Dealer or Distributor for service. |
| Engine starts from generator control panel but will not start automatically or from a remote panel. | Remote circuit breaker is tripped. | Reset breaker and restart. Contact a Cummins Dealer if breaker trips after resetting. |
| Engine will not crank. | Possible fault with control or starting system. | Check for the following conditions: - Fault lamp on. Correct fault and reset control. - Poor battery cable connections. Clean the battery cable terminals and tighten all connections. - Discharged or defective battery. Recharge or replace the battery. - Contact a Cummins Dealer or Distributor for assistance if none of the above. |
| No AC output voltage. | Field breaker is tripped. | Reset breaker. Contact a Cummins Dealer or Distributor if voltage build up causes breaker to trip. |
| Green:RUN lamp does not light following engine start-up. | Possible Start/Disconnect relay failure. | Contacta Cummins Dealer or Distributor 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: The monitor board or a sensor may be at fault.. See the table for the matching fixes.
Documented causes: Remote circuit breaker is tripped.. See the table for the matching fixes.
Documented causes: Possible fault with control or starting system.. See the table for the matching fixes.