Cummins/Onan MDGDB troubleshooting: 19 fault codes and symptom-cause-remedy entries from the manufacturer's own service documentation.
Cummins/Onan MDGDB — full specs, parts & maintenance.
All Cummins/Onan fault codes →
| Code | Meaning |
|---|---|
| Low Oil Pressure | Low oil pressure (lower than 14 ±2 PSI) |
| High Engine Temperature | High engine temperature (higher than 220 ±6°F) |
| High Exhaust Temperature | High exhaust temperature (higher than 190 ±9°F) |
| Symptom | Cause | Remedy |
|---|---|---|
| The engine does not crank. | Service the battery and battery terminals and cables. Replace the control circuit fuse if it has blown. | |
| The engine cranks, but does not start. | Service the battery and battery terminals and cables. Replace the control circuit fuse if it has blown. | |
| The engine coolant temperature gauge indicates 220° F or more while the engine is running. | Shut down the set if possible. Disconnect as many non-critical loads as possible so that the engine will run cooler, and service as soon as possible. | |
| The engine shuts down due to high engine temperature or low coolant level. | Shut down the set if possible. Disconnect as many non-critical loads as possible so that the engine will run cooler, and service as soon as possible. | |
| The engine oil pressure gauge indicates less than 20 psi. | Fill coolant, if necessary, after the engine has cooled down, and fix any leaks. See Maintenance for servicing the cooling system. | |
| The engine shuts down due to low oil pressure or low oil level. | Fill coolant, if necessary, after the engine has cooled down, and fix any leaks. See Maintenance for servicing the cooling system. | |
| There is no output because the line circuit breaker (if provided) or the field circuit breaker has tripped. | Reset the tripped fault circuit breaker. | |
| Breaker reset button extends out past normal | Push the button to restore operation (after the engine has been properly serviced) | |
| The engine coolant temperature gauge indicates 2200F or more while the engine is running. | Shut down the set if possible. See Maintenance for servicing the cooling system. | |
| The engine shuts down due to over-speed. | Check the governor-throttle linkage. See Adjustments. Reset the tripped fault circuit breaker. | |
| ENGINE DOES NOT CRANK | The batteries are worn out or discharged, the terminal connectors are loose or corroded or the battery cables are corroded. Control circuit fuse NO1 is blown. The local or pilot house Start / Run / Stop switch is faulty. Crank relay K104 or run relay K105 is faulty. The starter motor, motor solenoid, wire or connector is faulty. | Service or replace the batteries, terminal connectors and cables. Specific gravity for a fully charged battery is approximately 1.260 at 80° F (27°C). Service the engine-driven battery charging alternator in accordance with the engine service manual if normal battery charging voltage is not between 13 and 14 volts for 12 volt systems and between 26 and 28 volts for 24 volt systems. Replace the fuse with one of the same type and amp rating. Remove the control box cover and push the control switch to Start and hold it there. Replace the switch if it is open (infinite resistance) between terminals 2 and 3. Remove the control box cover and push the control switch to Start. Replace either relay if it does not 'click'. Repeat the test to make sure. Push the control switch to the Start position and hold it there. Check for battery voltage at the starter motor solenoid terminal. Service the starter motor or solenoid in accordance with the engine service manual if there is battery voltage at the terminal. If there is no voltage repair the wire (yellow/orange) or terminal 8 of connector J1/P1. |
| ENGINE CRANKS BUT DOES NOT START | The fuel supply tank is empty. The electronic governor or fuel solenoid valve K118 does not function. Engine temperature is too low for starting. Cranking speed is too slow because of low battery charge, loose or corroded terminal connectors, corroded battery cables or too much starter solenoid contact resistance. The fuel system has lost prime, the fuel lines or filters are plugged, the fuel lift pump is not working, the fuel is contaminated or the air filter is plugged. The engine fuel injection system is faulty. | Fill the fuel supply tank with the appropriate grade of fuel. The fuel solenoid valve (threaded into the fuel injection pump unit) should 'click' when the panel switch is pushed to the Start position. The electronic governor should also drive the fuel injection pump unit to the full power fuel position. Both are powered through engine block terminal T26 (located just below the injection unit). Service the electronic governor if there is battery voltage at terminal T26 during cranking but it does not function. See Engine Control. Replace the fuel solenoid if it does not function. If there is no voltage at terminal T26, check wires and connectors. Remove the control box cover, if necessary, to checkout run relay K105. It should 'click' when the control switch is pushed to Start. Repeat the test to make sure. Plug in, repair or install engine coolant and engine oil heaters. Replace the engine oil if it is not of the recommended viscosity for the ambient temperature. Service the batteries, terminal connectors, cables or starter solenoid. Cable, terminal or solenoid contact resistance is too high if there is more than 1 volt drop between battery and motor terminals for 12 volt systems and 2 volts drop for 24 volt systems while the engine is cranking. Service the engine-driven battery charging alternator in accordance with the engine service manual if normal battery charging voltage is not between 13 and |
| UNSTABLE OUTPUT VOLTAGE AT STABLE OPERATING SPEED | Adjust voltage regulator Vi321 as described under AC Control. Adjust engine speed as described under Engine Control. Check connections and wiring continuity in all circuits connected to the voltage regulator (exciter, alternator, PMG, voltage trimmer and field circuit breaker). Service as necessary. Replace voltage adjusting rheostat R21 if it is open. Replace voltage regulator VR21 if the connected circuits are okay. | |
| OUTPUT VOLTAGE TOO HIGH OR TOO LOW | Replace voltage regulator VR21 before servicing other faults can lead to damage to the new voltage regulator. Check the alternator output terminals and reconnect, if necessary, per the appropriate reconnection diagram (Page 7-6). | |
| NO OUTPUT THROUGH MOUNTED LINE CIRCUIT BREAKER | If the circuit breaker is in the tripped position, determine the cause; whether overload, ground fault or shunt trip. Service as required. If the circuit breaker is in the OFF Position, find out why, and make sure the set is in operating condition and available for use before throwing the switch ON. | |
| UNBALANCED OUTPUT VOLTAGE | Disconnect all loads from the generator set. Is output amperage still unbalanced? Check the alternator output terminals and reconnect, if necessary, per the appropriate reconnection diagram. Check for proper grounding of the neutral terminal. Check each stator winding for continuity and service as described under Generator Testing and Service. Check the loads for ground faults and service as required. |
Fault codes and symptom→remedy steps extracted from this model’s service/owner documentation; verify against the official manual before servicing.
Documented causes: The batteries are worn out or discharged, the terminal connectors are loose or corroded or the battery cables are corroded. Control circuit fuse NO1 is blown. The local or pilot house Start / Run / Stop switch is faulty. Crank relay K104 or run relay K105 is faulty. The starter motor, motor solenoid, wire or connector is faulty.. See the table for the matching fixes.
Documented causes: The fuel supply tank is empty. The electronic governor or fuel solenoid valve K118 does not function. Engine temperature is too low for starting. Cranking speed is too slow because of low battery charge, loose or corroded terminal connectors, corroded battery cables or too much starter solenoid contact resistance. The fuel system has lost prime, the fuel lines or filters are plugged, the fuel lift pump is not working, the fuel is contaminated or the air filter is plugged. The engine fuel injection system is faulty.. See the table for the matching fixes.