Cummins/Onan MDGBA troubleshooting: 29 symptom-cause-remedy entries from the manufacturer's own service documentation.
Cummins/Onan MDGBA — full specs, parts & maintenance.
All Cummins/Onan fault codes →
| Symptom | Cause | Remedy |
|---|---|---|
| Engine does not crank | The batteries are worn out or discharged, the terminal connectors are loose or corroded or the battery cables are corroded | 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. |
| Engine does not crank | Control circuit fuse NO1 is blown | Replace the fuse with one of the same type and amp rating. |
| Engine does not crank | The local or pilot house Start / Run / Stop switch is faulty | 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. |
| Engine does not crank | Crank relay K104 or run relay K105 is faulty | 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. |
| Engine does not crank | The starter motor, motor solenoid, wire or connector is faulty | 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 | Fill the fuel supply tank with the appropriate grade of fuel. |
| Engine cranks but does not start | The electronic governor or fuel solenoid valve K118 does not function | 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 check out run relay K105. It should "click" when the control switch is pushed to Start. Repeat the test to make sure. |
| Engine cranks but does not start | Engine temperature is too low for starting | 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. |
| Engine cranks but does not start | 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 | 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 14 volts for 12 volt systems and 26 and 28 volts for 24 volt systems. |
| Engine cranks but does not start | 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 | Bleed the fuel system in accordance with the Operator's Manual. If the engine still does not start, check out each of the other possibilities thoroughly and service. |
| Engine cranks but does not start | The engine fuel injection system is faulty | Service according to the appropriate engine service manual. |
| Engine runs until fault shutdown | The overspeed circuit breaker has tripped | Service and adjust the engine governor. See Engine Control. If the governor is functioning properly, readjust the electronic overspeed module to the proper setting. See Engine Control. |
| Engine runs until fault shutdown | The Low Oil Pressure or Low Oil Level circuit breaker has tripped | Refill with as much engine oil as necessary and repair any leaks before putting the set back into service. Start the engine and note the pressure indicated by the control panel gauge. If engine oil pressure is greater than 15 PSIG, the low oil pressure cutout switch is faulty and must be replaced. If engine oil pressure is less, service the lubricating oil system according to the engine service manual. |
| Engine runs until fault shutdown | The High Engine Temperature or Low Coolant Level circuit breaker has tripped | Refill with as much engine coolant as necessary and repair any leaks before putting the set back into service. Clean out the sea water strainer and make sure the sea water cock is fully open if the engine has a heat exchanger. Start the engine and note the temperature indicated by the control panel gauge. |
| Engine runs until fault shutdown | The High Exhaust Temperature or Low Water Flow circuit breaker has tripped | |
| Unstable output voltage at stable operating speed | Adjust voltage regulator VR21 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; Check the alternator output terminals and reconnect, if necessary, per the appropriate reconnection diagram (Page 7-6) | |
| Output voltage too high or too low | Adjust voltage regulator VR21 as described under AC Control; Check the rotating diode assembly, exciter stator winding, exciter rotor winding, rotor field winding and main stator winding. Service as described under Generator Testing and Service; Check connections and wiring continuity in all circuits connected to voltage regulator VR21 (exciter, alternator, PMG, voltage trimmer and field circuit breaker). Service as described under Generator Testing and Service; Check the alternator output terminals and reconnect, if necessary, per the appropriate reconnection diagram (Page 7-6) | |
| Field circuit breaker keeps tripping | Does AC output voltage build up to at least 150 percent of rated output before the breaker trips? If yes, adjust voltage regulator VR21 as described under AC Control; Check the rotating diode assembly, exciter stator winding, exciter rotor winding, rotor field winding and main stator winding. Service as described under Generator Testing and Service; Check connections and wiring continuity in all circuits connected to voltage regulator VR21 (exciter, alternator, PMG, voltage trimmer and field circuit breaker). Service as described under Generator Testing and Service; Check the alternator output terminals and reconnect, if necessary, per the appropriate reconnection diagram (Page 7-6) | |
| Unbalanced output voltage | Disconnect all loads from the generator set. Is output amperage still unbalanced? If no, check the loads for ground faults and service as required; Redistribute the load so that there is less than 10 percent variation between phases. Check for proper grounded neutral connections; 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 | |
| No output through mounted line circuit breaker | The circuit breaker is in the tripped position (overload, ground fault or shunt trip) | Determine the cause; whether overload, ground fault or shunt trip. Service as required. |
| No output through mounted line circuit breaker | 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. |
| The engine does not crank. | Service the battery and battery terminals and cables. See Maintenance. Replace control circuit fuse F101 if it has blown. | |
| The engine cranks, but does not start. | Check the fuel supply. If a fault circuit breaker has tripped, service the fault, and reset the circuit breaker. Service the battery if the engine cranks too slowly to start, refill with engine oil of suitable viscosity and plug in or service the engine coolant heater, if provided. Install an engine coolant heater if necessary. | |
| 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 high engine temperature or low coolant level. | Shut down the set if possible. See Maintenance for servicing the cooling system. | |
| 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 oil, if necessary. 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 over-speed. | Check the governor-throttle linkage. See Adjustments. Reset the tripped fault circuit breaker. | |
| There is no output because the line circuit breaker (if provided) or the field circuit breaker has tripped. | Determine the cause (overload or short circuit) and clear the fault. Reset the line circuit breaker. Reset the field circuit breaker. |
Fault codes and symptom→remedy steps extracted from this model’s service/owner documentation; verify against the official manual before servicing.
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. See the table for the matching fixes.
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. See the table for the matching fixes.
Documented causes: The overspeed circuit breaker has tripped; The Low Oil Pressure or Low Oil Level circuit breaker has tripped; The High Engine Temperature or Low Coolant Level circuit breaker has tripped; The High Exhaust Temperature or Low Water Flow circuit breaker has tripped. See the table for the matching fixes.