Fault codes / Onan generator / 25

Onan generator code 25

What it means: Alternator over voltage.

What to check

Alternator control fault. Service.

Learn the system

• Generators
• Transfer switches and generator power

Practice it on a service call

• Generator starts then quits
• Generator runs but coach has no power
• Generator cranks but won't start

Guided diagnosis

• Generator

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 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 51 Processor malfunction
• 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.