Generac generator fault codes

Every Generac engine fault code in our verified reference — 30 codes, 25 of them with a documented remedy. Find your code in the table, read the likely causes, then work the remedy. If it is beyond a field fix, our workshop in Embakasi repairs Generac controllers and engines at board level.

Covers: 2 Cylinder Units · 5500 · Single Cylinder Units · Various

Generac generator engine fault codes with causes and remedies
Code	Fault	Likely cause	Remedy
2	Low oil pressure fault (Low oil pressure cutoff switch did not open).	—	Check engine oil level and add oil as necessary. Drain excess oil (above dipstick Full mark).; Check wiring and connections. Inspect hand throttle sensor. Reset ECU and test.
3	Service check fault (Indicates fault with second-level fault code).	—	Check the second-level fault code by pressing STOP once. The second-level fault code will have two-digits. The faults are listed in numerical order in this table.; Check actuator wiring and connections. Inspect EGR or throttle valve. Reset ECU and test.
3	Service Check Fault (First-level fault code—Indicates fault with second-level fault code).	spark plug	Check the second-level fault code by pressing STOP once. The second-level fault code will have two digits. The faults are listed in numerical order in the table.
4	Overcrank fault (Cranking exceeded 30 seconds without engine starting).	Gasoline Models – Check and fill the fuel tank; as necessary. (Note: The genset fuel pickup tube is probably higher up in the fuel tank than the vehicle engine pickup.) Prime the engine fuel system by holding the control switch at Stop/Prime for 30 seconds. Low Pressure LPG Models – Check and fill the LPG container; as necessary. On cold days the LPG container may have to be kept at least half full to provide the rate of vaporization necessary to keep up with the genset fuel demand. High Pressure LPG Models – Check and fill the LPG container; as necessary; and drain the genset LPG system of oil that may have migrated from the supply system. Make sure to re-close the drain valve. Open any closed fuel valves. Secure the spark plug leads on the spark plugs. Replace the spark plugs. Service the air cleaner.	Check actuator wiring and connections. Inspect EGR or throttle valve. Reset ECU and test.
4	Overcrank Fault (First-level fault code—Cranking exceeded 20 seconds without engine starting).	Gasoline Models - Check and fill the fuel tank; as necessary. (Note: The genset fuel pickup tube is probably higher up in the fuel tank than the vehicle engine pickup.) Prime the engine fuel system by holding the control switch at Stop/Prime for 30 seconds. LPG Models - Check and fill the LPG container; as necessary. On cold days the LPG container may have to be kept at least half full to provide the rate of vaporization necessary to keep up with the genset fuel demand. Open any closed fuel valves. Secure the spark plug lead on the spark plug. Replace the spark plug. Service the air cleaner.	reprogram or replace ECU. Contact Deutz service.
12	Overvoltage fault (Controller unable to maintain rated voltage).	See an authorized Onan dealer.	Check actuator wiring and connections. Inspect EGR or throttle valve. Reset ECU and test.
12	Overvoltage Fault (Controller unable to maintain rated voltage).	See an authorized Onan dealer.; overheating	—
13	Undervoltage fault (Controller unable to maintain rated voltage).	Reduce the number of connected appliances	Check actuator wiring and connections. Inspect EGR or throttle valve. Reset ECU and test.
13	Undervoltage Fault (Controller unable to maintain rated voltage).	Reduce the number of connected appliances; injectors	—
14	Overfrequency fault (Engine governor unable to maintain rated frequency).	See an authorized Onan dealer.	Check actuator wiring and connections. Inspect EGR or throttle valve. Reset ECU and test.
14	Overfrequency Fault (Engine governor unable to maintain rated frequency).	See an authorized Onan dealer.; stopping the unit immediately.	—
15	Underfrequency fault (Engine governor unable to maintain rated frequency).	Reduce the number of connected appliances; especially when air conditioners and battery chargers are running. High Pressure LPG Models – Drain the genset LPG system of oil that may have migrated from the supply system. Make sure to re-close the drain valve.	Check actuator wiring and connections. Inspect EGR or throttle valve. Reset ECU and test.
19	Governor actuator fault (Controller sensed open or shorted circuit).	See an authorized Onan dealer.	Check actuator wiring and connections. Inspect EGR or throttle valve. Reset ECU and test.
22	Governor actuator overload fault (Duration of operation at or near full-duty cycle beyond design limit).	Reduce the number of connected appliances; especially when air conditioners and battery chargers are running. Service the air cleaner. Check for and repair a blocked exhaust system.	replace ECU. Contact Deutz service.
23	Low oil pressure cutoff switch fault (Controller sensed switch still open during start—not a running fault).	See an authorized Onan dealer.	reprogram or replace ECU. Contact Deutz service.
27	Voltage sense fault (Controller unable to sense output voltage).	See an authorized Onan dealer.; spark plug	—
29	High battery voltage fault (Voltage across battery system greater than 19 volts).	spark plug	Check battery bank connections and reconnect if necessary so that the 12 volt batteries serving the genset are connected in parallel (12 volt) rather than in series (24 volt). Select a lower battery boost charge rate.
31	Overspeed fault (Engine speed greater than 3400 rpm).	See an authorized Onan dealer.; spark plug	—
1500	Overspeed. Engine speed exceeds safe operating limits.	or Incorrect	Contact service for speed control issues
1501	RPM Sensor Loss for a 2 cylinder unit already running.	ignition coils; and engine load; or Period	Check fuel
1505	RPM Sensor Loss for a 2 cylinder unit cranking.	starter; wiring; and ignition coils; or Incorrect	Check battery
1511	RPM Sensor Loss for a single cylinder unit already running.	ignition coil; and engine load; or Incorrect	Check fuel
1515	RPM Sensor Loss for a single cylinder unit cranking.	starter; wiring; and ignition coil; or Period	Check battery
1600	Internal fault / Underspeed. Internal component failure or wiring issues / Overloaded or throttle control problem.	or Incorrect	Contact service for internal faults / Check load and throttle control
1603	Engine never reached rated 3600 RPM speed during startup.	fuel system; and fuel selector; or Period	Check stepper motor; check engine RPM and correct issues
1610	Overcurrent. Generator output current exceeds safe operating levels.	Reduce load and check electrical connections	Check oil level and pressure. Inspect sensor and wiring. Adjust setpoints if necessary.
1620	Underfrequency. Generator output frequency drops below acceptable levels.	—	Contact service for frequency control issues; Check coolant temperature. Inspect sensor and wiring. Ensure temperature is above setpoint.
1630	Over frequency. Generator output frequency exceeds acceptable levels.	waiting until the ECU has shut off and switching ignition on again. Check if the error is still active.	Contact service for frequency control issues; Check the cabling for a short circuit/cable break; repair/replace cables if necessary. Check the particular component for damage or the need of maintenance; repair/replace it if necessary. Reset the ECU by switching ignition off
1710	Overload. Generator output load exceeds safe operating levels.	Reduce load and check sensing circuit; waiting until the ECU has shut off and switching ignition on again. Check if the error is still active.	Check the cabling for a short circuit/cable break; repair/replace cables if necessary. Check the particular component for damage or the need of maintenance; repair/replace it if necessary. Reset the ECU by switching ignition off
1800	Overvoltage for a prolonged period.	—	Check voltage regulator and wiring for issues; Check wiring and connections. Inspect hand throttle sensor. Reset ECU and test.

Codes and descriptions are industry-standard identifiers reproduced for identification only. This reference is not affiliated with or endorsed by Generac; for official procedures always refer to the manufacturer’s service manual for your specific engine. A dash means our registry holds no verified entry for that column — we publish the gap rather than fill it in.

Cannot clear the fault?

Send us the code and the engine serial. We diagnose Generac sets on site across all 47 counties, and repair controllers at board level on the bench in Embakasi.

Generac generator fault codes

Covers: 2 Cylinder Units · 5500 · Single Cylinder Units · Various

Generac generator engine fault codes with causes and remedies
Code	Fault	Likely cause	Remedy
2	Low oil pressure fault (Low oil pressure cutoff switch did not open).	—	Check engine oil level and add oil as necessary. Drain excess oil (above dipstick Full mark).; Check wiring and connections. Inspect hand throttle sensor. Reset ECU and test.
3	Service check fault (Indicates fault with second-level fault code).	—	Check the second-level fault code by pressing STOP once. The second-level fault code will have two-digits. The faults are listed in numerical order in this table.; Check actuator wiring and connections. Inspect EGR or throttle valve. Reset ECU and test.
3	Service Check Fault (First-level fault code—Indicates fault with second-level fault code).	spark plug	Check the second-level fault code by pressing STOP once. The second-level fault code will have two digits. The faults are listed in numerical order in the table.
4	Overcrank fault (Cranking exceeded 30 seconds without engine starting).	Gasoline Models – Check and fill the fuel tank; as necessary. (Note: The genset fuel pickup tube is probably higher up in the fuel tank than the vehicle engine pickup.) Prime the engine fuel system by holding the control switch at Stop/Prime for 30 seconds. Low Pressure LPG Models – Check and fill the LPG container; as necessary. On cold days the LPG container may have to be kept at least half full to provide the rate of vaporization necessary to keep up with the genset fuel demand. High Pressure LPG Models – Check and fill the LPG container; as necessary; and drain the genset LPG system of oil that may have migrated from the supply system. Make sure to re-close the drain valve. Open any closed fuel valves. Secure the spark plug leads on the spark plugs. Replace the spark plugs. Service the air cleaner.	Check actuator wiring and connections. Inspect EGR or throttle valve. Reset ECU and test.
4	Overcrank Fault (First-level fault code—Cranking exceeded 20 seconds without engine starting).	Gasoline Models - Check and fill the fuel tank; as necessary. (Note: The genset fuel pickup tube is probably higher up in the fuel tank than the vehicle engine pickup.) Prime the engine fuel system by holding the control switch at Stop/Prime for 30 seconds. LPG Models - Check and fill the LPG container; as necessary. On cold days the LPG container may have to be kept at least half full to provide the rate of vaporization necessary to keep up with the genset fuel demand. Open any closed fuel valves. Secure the spark plug lead on the spark plug. Replace the spark plug. Service the air cleaner.	reprogram or replace ECU. Contact Deutz service.
12	Overvoltage fault (Controller unable to maintain rated voltage).	See an authorized Onan dealer.	Check actuator wiring and connections. Inspect EGR or throttle valve. Reset ECU and test.
12	Overvoltage Fault (Controller unable to maintain rated voltage).	See an authorized Onan dealer.; overheating	—
13	Undervoltage fault (Controller unable to maintain rated voltage).	Reduce the number of connected appliances	Check actuator wiring and connections. Inspect EGR or throttle valve. Reset ECU and test.
13	Undervoltage Fault (Controller unable to maintain rated voltage).	Reduce the number of connected appliances; injectors	—
14	Overfrequency fault (Engine governor unable to maintain rated frequency).	See an authorized Onan dealer.	Check actuator wiring and connections. Inspect EGR or throttle valve. Reset ECU and test.
14	Overfrequency Fault (Engine governor unable to maintain rated frequency).	See an authorized Onan dealer.; stopping the unit immediately.	—
15	Underfrequency fault (Engine governor unable to maintain rated frequency).	Reduce the number of connected appliances; especially when air conditioners and battery chargers are running. High Pressure LPG Models – Drain the genset LPG system of oil that may have migrated from the supply system. Make sure to re-close the drain valve.	Check actuator wiring and connections. Inspect EGR or throttle valve. Reset ECU and test.
19	Governor actuator fault (Controller sensed open or shorted circuit).	See an authorized Onan dealer.	Check actuator wiring and connections. Inspect EGR or throttle valve. Reset ECU and test.
22	Governor actuator overload fault (Duration of operation at or near full-duty cycle beyond design limit).	Reduce the number of connected appliances; especially when air conditioners and battery chargers are running. Service the air cleaner. Check for and repair a blocked exhaust system.	replace ECU. Contact Deutz service.
23	Low oil pressure cutoff switch fault (Controller sensed switch still open during start—not a running fault).	See an authorized Onan dealer.	reprogram or replace ECU. Contact Deutz service.
27	Voltage sense fault (Controller unable to sense output voltage).	See an authorized Onan dealer.; spark plug	—
29	High battery voltage fault (Voltage across battery system greater than 19 volts).	spark plug	Check battery bank connections and reconnect if necessary so that the 12 volt batteries serving the genset are connected in parallel (12 volt) rather than in series (24 volt). Select a lower battery boost charge rate.
31	Overspeed fault (Engine speed greater than 3400 rpm).	See an authorized Onan dealer.; spark plug	—
1500	Overspeed. Engine speed exceeds safe operating limits.	or Incorrect	Contact service for speed control issues
1501	RPM Sensor Loss for a 2 cylinder unit already running.	ignition coils; and engine load; or Period	Check fuel
1505	RPM Sensor Loss for a 2 cylinder unit cranking.	starter; wiring; and ignition coils; or Incorrect	Check battery
1511	RPM Sensor Loss for a single cylinder unit already running.	ignition coil; and engine load; or Incorrect	Check fuel
1515	RPM Sensor Loss for a single cylinder unit cranking.	starter; wiring; and ignition coil; or Period	Check battery
1600	Internal fault / Underspeed. Internal component failure or wiring issues / Overloaded or throttle control problem.	or Incorrect	Contact service for internal faults / Check load and throttle control
1603	Engine never reached rated 3600 RPM speed during startup.	fuel system; and fuel selector; or Period	Check stepper motor; check engine RPM and correct issues
1610	Overcurrent. Generator output current exceeds safe operating levels.	Reduce load and check electrical connections	Check oil level and pressure. Inspect sensor and wiring. Adjust setpoints if necessary.
1620	Underfrequency. Generator output frequency drops below acceptable levels.	—	Contact service for frequency control issues; Check coolant temperature. Inspect sensor and wiring. Ensure temperature is above setpoint.
1630	Over frequency. Generator output frequency exceeds acceptable levels.	waiting until the ECU has shut off and switching ignition on again. Check if the error is still active.	Contact service for frequency control issues; Check the cabling for a short circuit/cable break; repair/replace cables if necessary. Check the particular component for damage or the need of maintenance; repair/replace it if necessary. Reset the ECU by switching ignition off
1710	Overload. Generator output load exceeds safe operating levels.	Reduce load and check sensing circuit; waiting until the ECU has shut off and switching ignition on again. Check if the error is still active.	Check the cabling for a short circuit/cable break; repair/replace cables if necessary. Check the particular component for damage or the need of maintenance; repair/replace it if necessary. Reset the ECU by switching ignition off
1800	Overvoltage for a prolonged period.	—	Check voltage regulator and wiring for issues; Check wiring and connections. Inspect hand throttle sensor. Reset ECU and test.

Cannot clear the fault?

Send us the code and the engine serial. We diagnose Generac sets on site across all 47 counties, and repair controllers at board level on the bench in Embakasi.