Generac MMG35DF4 troubleshooting: 58 fault codes and 46 symptom-cause-remedy entries from the manufacturer's own service documentation.
Generac MMG35DF4 — full specs, parts & maintenance.
| Code | Meaning | Cause | Remedy |
|---|---|---|---|
| HIGH TEMPERATURE | Unit shuts down during operation. | Check ventilation around the intake, exhaust and rear of generator. Contact Independent Authorized Servicing Dealer if no obstruction is found. | |
| OVERLOAD REMOVE LOAD | Unit shuts down during operation. | Clear alarm and remove household loads from the generator. Put back in AUTO and restart. | |
| RPM SENSE LOSS | Unit was running and shuts down, attempts to restart. | Clear alarm and remove household loads from the generator. Put back in AUTO and restart. If problem returns, contact Independent Authorized Servicing Dealer to investigate possible fuel issue. | |
| NOT ACTIVATED | Unit will not start in AUTO with 2-wire start signal. | Refer to Activation. | |
| LOW OIL PRESSURE | Unit will not start in AUTO with 2-wire start signal. | Check oil level. Add oil per Owner's Manual. Contact Independent Authorized Servicing Dealer if oil level is correct. | |
| RPM SENSE LOSS | Unit will not start in AUTO with 2-wire start signal. | Clear alarm. Navigate to the BATTERY MENU on the control pad LCD. Contact Independent Authorized Servicing Dealer if battery is GOOD. Replace battery If CHECK BATTERY is displayed. | |
| OVERCRANK | Unit will not start in AUTO with 2-wire start signal. | Check fuel line shutoff valve is in the ON position. Clear alarm. Attempt to start the unit in MANUAL. If it does not start or starts and runs rough, contact Independent Authorized Servicing Dealer. | |
| LOW VOLTS REMOVE LOAD | Unit will not start in AUTO with 2-wire start signal. | Clear alarm and remove household loads from the generator. Set back to AUTO and restart. | |
| FUSE PROBLEM | Unit will not start in AUTO with 2-wire start signal. | Check ATO 7.5 Amp fuse. Replace with same type fuse if bad. Contact Independent Authorized Servicing Dealer if fuse is good. | |
| OVERSPEED | Unit will not start in AUTO with 2-wire start signal. | Contact Independent Authorized Servicing Dealer. | |
| UNDER VOLTAGE | Unit will not start in AUTO with 2-wire start signal. | Contact Independent Authorized Servicing Dealer. | |
| UNDERSPEED | Unit will not start in AUTO with 2-wire start signal. | Contact Independent Authorized Servicing Dealer. | |
| STEPPER OVERCURRENT | Unit will not start in AUTO with 2-wire start signal. | Contact Independent Authorized Servicing Dealer. | |
| MISWIRE | Unit will not start in AUTO with 2-wire start signal. | Contact Independent Authorized Servicing Dealer. | |
| 1048 | VSCF Overload — Unit shuts down during operation. | Alternator, AVR or wiring is damaged. | Contact Independent Authorized Servicing Dealer. |
| 1049 | VSCF Overload — Unit shuts down during operation. | Generator output is shorted or severely overloaded. | Identify and clear the overload, and then restart. |
| 1051 | VSCF High Battery — Yellow LED illuminated in any state. | Voltage supply to the AVR is high. | If an external battery charger is in use, contact installing dealer to correct installation. If an external battery charger is NOT in use, contact Independent Authorized Servicing Dealer. |
| 1052 | VSCF DC Overvoltage — Unit shuts down during operation. | The generator was temporarily overloaded; The output was temporarily shorted. | Try to restart the unit. |
| 1053 | VSCF Gate Fault — Unit shuts down during operation or starting. | AVR is damaged. | Contact Independent Authorized Servicing Dealer. |
| 1054 | VSCF IGBT Overtemp. — Unit shuts down during operation or starting. | Replace AVR filter. Inspect fan. | Replace AVR filter. Inspect fan. |
| 1054 | VSCF IGBT Overtemp. — Unit shuts down during operation or starting. | Intake or exhaust air path is blocked. | Check intake and exhaust. |
| 1054 | VSCF IGBT Overtemp. — Unit shuts down during operation or starting. | Air leak in AVR enclosure. | Contact Independent Authorized Servicing Dealer. |
| 1054 | VSCF IGBT Overtemp. — Unit shuts down during operation or starting. | Engine running too hot. | Inspect air intake and exhaust. |
| 1054 | VSCF IGBT Overtemp. — Unit shuts down during operation or starting. | Ambient temperature has risen above 60º F (15.5 °C). | Derate the generator output per specifications. |
| 1055 | VSCF Phase Error — Unit shuts down during starting. | An incorrect voltage and frequency has been detected during starting. Alternator damage. | Contact Independent Authorized Servicing Dealer. |
| 1055 | VSCF Phase Error — Unit shuts down during starting. | Generator has started into a severe load. | Manually operate generator breaker and try to restart unit. If problem persists, remove load and attempt to restart unit again. |
| 1055 | VSCF Phase Error — Unit shuts down during starting. | The engine may not be reaching its prescribed speed. | Verify stepper motor is moving and linkage is free; Verify stepper motor is plugged in; Verify gas pressure is within specified limits. |
| 1056 | VSCF Undervoltage — Unit shuts down during operation or starting. | The generator output voltage is too low. The load is too large. | Remove load and attempt to restart unit. |
| 1056 | VSCF Undervoltage — Unit shuts down during operation or starting. | Alternator or AVR damage. | Contact Independent Authorized Servicing Dealer. |
| 1057 | VSCF Overvoltage — Unit shuts down during operation or starting. | The generator has been overloaded. | Remove load and attempt to restart unit. |
| 1057 | VSCF Overvoltage — Unit shuts down during operation or starting. | Generator has started into a severe load. | Manually operate generator breaker and try to restart unit. If problem persists, remove load and attempt to restart unit again. |
| 1058 | VSCF DC Undervoltage — Unit shuts down during operation or starting. | The DPE winding supplies this voltage. Alternator damage. | Contact Independent Authorized Servicing Dealer. |
| 1059 | VSCF Field Loss — Unit shuts down during starting. | Unit detects no output voltage while starting. Alternator damage. | Contact Independent Authorized Servicing Dealer. |
| 1061 | VSCF Field Loss — Unit shuts down during operation. | Unit detects loss of output voltage while running. Alternator damage. | Contact Independent Authorized Servicing Dealer. |
| 1060 | Big Fan Failure — Unit shuts down during operation. | This alarm occurs when the AVR electronics temperature exceeds 70 C. AVR filter faulty. | Replace AVR filter. |
| 1060 | Big Fan Failure — Unit shuts down during operation. | Intake or exhaust air path is blocked. | Check intake and exhaust. |
| 1060 | Big Fan Failure — Unit shuts down during operation. | Air leak in AVR enclosure. | Contact Independent Authorized Servicing Dealer. |
| 1060 | Big Fan Failure — Unit shuts down during operation. | Engine running too hot. | Inspect air intake and exhaust. |
| 1060 | Big Fan Failure — Unit shuts down during operation. | Ambient temperature has risen above 60º F (15.5 °C). | Derate the generator output per specifications. |
| 1060 | Big Fan Failure — Unit shuts down during operation. | If message is displayed when generator is stopped, also check SMALL fan. Small fan RUNS for 60 minutes after generator is stopped and keeps electronics cool during heat soak. | |
| 1065 | Overfrequency — Unit shuts down during operation. | Overload. | Remove load and attempt to restart unit. |
| 1065 | Overfrequency — Unit shuts down during operation. | RPM sensor has failed. | Contact Independent Authorized Servicing Dealer. |
| 1065 | Overfrequency — Unit shuts down during operation. | Stepper motor problem. | Contact Independent Authorized Servicing Dealer. |
| 1066 | VSCF Speed mismatch — Unit shuts down during Operation or starting. | Fuel problem (pressure loss). | Check fuel supply and attempt to restart unit. |
| 1066 | VSCF Speed mismatch — Unit shuts down during Operation or starting. | Large overload. | Remove load and attempt to restart unit. |
| 1066 | VSCF Speed mismatch — Unit shuts down during Operation or starting. | Throttle or engine problem. | Contact Independent Authorized Servicing Dealer. |
| 1070 | Small fan failure — "Small fan failure" is displayed. If unit was running in AUTO, it will continue to run for one hour to cool electronics without fan. | Small fan current incorrect. Fan wiring or mechanical problem. | Contact Independent Authorized Servicing Dealer. |
| 1049 VSCF | Overload RED Unit shuts down during operation. | Check the LEDs/Screen for alarms. Generator output is shorted or severely overloaded. Identify and clear the overload, and then restart. | |
| 1051 VSCF | High Battery YELLOW LED illuminated in any state. | Check the LEDs/Screen for alarms. Voltage supply to the AVR is high. If an external battery charger is in use, contact installing dealer to correct installation. If an external battery charger is NOT in use, contact Independent Authorized Servicing Dealer. | |
| 1052 VSCF | DC Overvoltage RED Unit shuts down during operation. | Check the LEDs/Screen for alarms. Probable causes are: 1) The generator was temporarily overloaded. 2) The output was temporarily shorted. Try to restart the unit. | |
| 1053 VSCF | Gate Fault RED Unit shuts down during operation or starting. | Check the LEDs/Screen for alarms. AVR is damaged. Contact Independent Authorized Servicing Dealer. | |
| 1055 VSCF | Phase Error RED Unit shuts down during starting. | Check the LEDs/Screen for alarms. An incorrect voltage and frequency has been detected during starting. Probable causes are: 1) Alternator damage. Contact Independent Authorized Servicing Dealer. 2) Generator has started into a severe load. Manually operate generator breaker and try to restart unit. If problem persists, remove load and attempt to restart unit again. 3) The engine may not be reaching its prescribed speed. Proceed as follows: •Verify stepper motor is moving and linkage is free. •Verify stepper motor is plugged in. •Verify gas pressure is within specified limits. | |
| 1056 VSCF | Undervoltage RED Unit shuts down during operation or starting. | Check the LEDs/Screen for alarms. The generator output voltage is too low. Probable causes are: 1) The load is too large. Remove load and attempt to restart unit. 2) Alternator or AVR damage. Contact Independent Authorized Servicing Dealer. | |
| 1057 VSCF | Overvoltage RED Unit shuts down during operation or starting. | Check the LEDs/Screen for alarms. Probable causes are: 1) The generator has been overloaded. Remove load and attempt to restart unit. 2) Generator has started into a severe load. Manually operate generator breaker and try to restart unit. If problem persists, remove load and attempt to restart unit again. | |
| 1058 VSCF | DC Undervoltage RED Unit shuts down during operation or starting. | Check the LEDs/Screen for alarms. The DPE winding supplies this voltage. 1) Alternator damage. Contact Independent Authorized Servicing Dealer. | |
| 1059 VSCF | Field Loss RED Unit shuts down during starting. | Check the LEDs/Screen for alarms. Unit detects no output voltage while starting. 1) Alternator damage. Contact Independent Authorized Servicing Dealer. | |
| 1061 VSCF | Field Loss RED Unit shuts down during operation. | Check the LEDs/Screen for alarms. Unit detects loss of output voltage while running. 1) Alternator damage. Contact Independent Authorized Servicing Dealer. | |
| 1066 VSCF | Speed mismatch RED Unit shuts down during Operation or starting. | Check the LEDs/Screen for alarms. Probable causes are: 1) Fuel problem (pressure loss). Check fuel supply and attempt to restart unit. 2) Large overload. Remove load and attempt to restart unit. 3) Throttle or engine problem. Contact Independent Authorized Servicing Dealer. |
| Symptom | Cause | Remedy |
|---|---|---|
| Low Fuel Level Shutdown | Fuel level low or unit not sitting level; leaks in fuel tank; fuel level sender or connecting wiring damaged | Check fuel level on the LCD window and verify the unit is sitting level; check for leaks in fuel tank; check the fuel level sender and the connecting wiring for damage and check for continuity between the sender and the engine controller |
| Low Oil Pressure Shutdown | Engine oil level low; oil leaks; loss of oil pressure; oil pressure sender fault | Check engine oil level with the dipstick and add oil if required; visually inspect engine for oil leaks; restart the unit and verify the loss of oil pressure, shutting the engine down immediately if the oil pressure value does not read 5 psi (34 kPa) within five seconds; check oil pressure sender per the troubleshooting section of the engine operator's manual |
| Low Coolant Level Shutdown | Coolant level low; leaks in coolant hoses, engine block or water pump; coolant mixed with engine oil | Allow engine to cool; check coolant level in the radiator and add coolant until it is 3/4 in. (2 cm) below the filler neck, then secure the radiator cap; inspect coolant hoses, engine block and water pump for visible leaks; check engine oil to verify no coolant has mixed with it and see the engine operator's manual |
| High Coolant Temperature Shutdown | Coolant level low | Check coolant level in the overflow jug; restart engine and read the coolant temperature to verify a high coolant temperature shutdown, stopping engine immediately if the coolant temperature is 230°F (110°C) or more; allow engine to cool, add coolant to the overflow jug if it is low and check the level of coolant in the radiator |
| Low fuel level Shutdown | Low fuel level | Check fuel level in LCD window of controller. |
| Low fuel level Shutdown | Unit not level | Confirm that unit is sitting level to ensure an accurate reading. |
| Low fuel level Shutdown | Fuel tank leaking | Check tank for leaks. |
| Low fuel level Shutdown | Damaged fuel sender or wiring | Check for continuity between sender and engine controller. (See Wiring Diagrams.) |
| Low oil pressure shutdown | Low oil level | Check oil level on dipstick. Add oil, if needed. |
| Low oil pressure shutdown | Oil leaking from engine | Visually inspect the engine for leaks. Restart unit and verify loss of pressure. Shut down immediately if pressure does not reach 5 psi (34 kPa) within five seconds. |
| Low oil pressure shutdown | Oil pressure sender | See engine operator’s manual to identify corrective action. |
| Low coolant level shutdown | Low coolant level | Allow engine to cool, then check coolant level in radiator. Add coolant, if needed. |
| Low coolant level shutdown | Coolant hoses leaking | Inspect hoses for leaks. Repair or replace as necessary. |
| Low coolant level shutdown | Engine block or water pump leaking | Visually inspect for leaks. Verify no coolant has mixed with the engine oil (oil will appear milky). See engine operator’s manual for additional information. |
| High coolant temperature shutdown | Low coolant level | Add coolant if needed. Allow engine to cool, then check coolant level in radiator. Restart engine and check coolant temperature (on controller). Stop engine immediately if temperature is 210 °F (99 °C) or 230 °F (110 °C). |
| High coolant temperature shutdown | Blockage in radiator | Check radiator shroud and ducting for blockage and remove any foreign matter. |
| High coolant temperature shutdown | Leakage in coolant hoses, engine block, or water pump | Inspect for visible leaks. Check tension of water pump serpentine drive belt. |
| Overcrank shutdown | Fuel level low | Check fuel level in tank. |
| Overspeed or underspeed shutdown | Frequency setting incorrect | Disconnect all loads and restart unit. Read frequency (Hz) in the LCD window on controller. Frequency should read 60 Hz. |
| Engine will not crank. | Fuse blown. | Correct short circuit condition by replacing 7.5 Amp fuse. |
| Engine will not crank. | Loose, corroded or defective battery cables. | Tighten, clean or replace as necessary.* |
| Engine will not crank. | Defective starter contact. | Tighten, clean or replace as necessary.* |
| Engine will not crank. | Defective starter motor. | Tighten, clean or replace as necessary.* |
| Engine will not crank. | Dead battery. | Charge or replace battery. |
| Engine cranks but will not start. | Out of fuel. | Replenish fuel / Turn on fuel valve. |
| Engine cranks but will not start. | Defective fuel solenoid (FS). | * |
| Engine cranks but will not start. | Defective spark plug(s). | Clean, check gap, or replace plug(s). |
| Engine cranks but will not start. | Valve clearance needs adjustment. | Adjust valve clearance. |
| Engine starts hard and runs rough. | Air cleaner plugged or damaged. | Check / replace air cleaner. |
| Engine starts hard and runs rough. | Defective spark plug(s). | Clean, check gap, or replace plug(s). |
| Engine starts hard and runs rough. | Fuel regulator not set. | Set fuel regulator. |
| Engine starts hard and runs rough. | Fuel pressure incorrect. | Confirm fuel pressure to regulator is 10–12 in. water column (19–22 mm mercury) for LP, and 3.5–7 in. water column (7–13 mm mercury) for natural gas. |
| Engine starts hard and runs rough. | Fuel selector in wrong position. | Move selector to correct position. |
| Generator is set to OFF, but the engine continues to run. | Control board wired incorrectly. | Repair wiring or replace control board.* |
| Generator is set to OFF, but the engine continues to run. | Defective control board. | Replace control board. |
| No AC output from generator. | Main line circuit breaker is in the OFF (or OPEN) position. | Reset circuit breaker to ON (or CLOSED). |
| No AC output from generator. | Generator internal failure. | * |
| Unit consumes large amounts of oil. | Oil tank is over filled with oil. | Adjust oil to proper level. |
| Unit consumes large amounts of oil. | Engine breather defective. | * |
| Unit consumes large amounts of oil. | Improper type or viscosity of oil. | See Engine Oil Recommendations. |
| Unit consumes large amounts of oil. | Damaged gasket, seal or hose. | Check for oil leaks. |
| Unit running in AUTO but no power in house. | Contact Independent Authorized Servicing Dealer if Generator Disconnect circuit breaker is in the ON position. | |
| Unit will not start in AUTO with 2-wire start signal. | Check screen for start delay countdown. If the start up delay is greater than expected, contact Independent Authorized Servicing Dealer to adjust from 2 to 1500 seconds. | |
| Generator stalls when large load is supplied. | Total load is too big for the generator. | Loads must be less than 10 kW or 2 hp when operating under 3600 rpm. Contact installing dealer to correct installation. |
| Output voltage is low/high. | Voltage calibration incorrect. | Contact Independent Authorized Servicing Dealer. |
| Generator does not pull full power. | Current calibration incorrect. | Contact Independent Authorized Servicing Dealer. |
Fault codes and symptom→remedy steps extracted from this model’s service/owner documentation; verify against the official manual before servicing.
Documented causes: This alarm occurs when the AVR electronics temperature exceeds 70 C. AVR filter faulty.; Intake or exhaust air path is blocked.; Air leak in AVR enclosure.; Engine running too hot.. See the table for the matching fixes.
Documented causes: Fuse blown.; Loose, corroded or defective battery cables.; Defective starter contact.; Defective starter motor.. See the table for the matching fixes.
Documented causes: Air cleaner plugged or damaged.; Defective spark plug(s).; Fuel regulator not set.; Fuel pressure incorrect.. See the table for the matching fixes.