Fault codes / Onan generator / 51
Onan generator code 51
What it means: Processor malfunction.
What to check
Power cycle. If it returns, replace the control board.
Learn the system
Practice it on a service call
Guided diagnosis
Other Onan generator codes
- Onan generator code 2 Low oil pressure
- Onan generator code 3 Service check: a two-digit code is stored
- Onan generator code 4 Over crank: 30 seconds without starting
- Onan generator code 12 Output over voltage
- Onan generator code 13 Output under voltage
- Onan generator code 14 Output over frequency
- Onan generator code 15 Output under frequency
- Onan generator code 19 Throttle actuator circuit fault
- Onan generator code 22 Governor actuator overload: near full duty too long
- Onan generator code 25 Alternator over voltage
- Onan generator code 26 Alternator under voltage
- Onan generator code 27 Pma sense lost
- Onan generator code 29 Battery over voltage
- Onan generator code 31 Over speed: above 3400 rpm
- Onan generator code 32 Low cranking speed: under 180 rpm for 2 s
- Onan generator code 35 Control card failure (EEPROM)
- Onan generator code 36 Engine stopped without a stop command
- Onan generator code 37 Invalid generator set configuration
- Onan generator code 38 Over current / field overload
- Onan generator code 41 Generator rotor: can't sense field or output voltage
- Onan generator code 42 Processor ROM error
- Onan generator code 43 Processor RAM error
- Onan generator code 45 Speed sense: can't sense quadrature frequency
- Onan generator code 47 Ignition: control can't sense ignition
- Onan generator code 48 Generator field sense
- Onan generator code 52 Fuel injector open or short (EFI models)
- Onan generator code 54 Mat sender open or short (efi)
- Onan generator code 56 Map sender open or short (efi)
- Onan generator code 57 Over prime: more than 3 minutes
- Onan generator code 58 Exhaust gas temperature over 650°C (1202°F)
- Onan generator code 81 Egt sensor open
- Onan generator code 82 Egt sensor shorted
Full field guide: Cummins Onan RV generator
Codes come from the maker manuals and public service sheets. Your model's own chart always wins, and LP and 120 volt work belongs to a qualified technician.