Onan

OVERSPEED

UnclassifiedCooling

What This Code Means

Engine fails to crank with switch in RUN position; Engine malfunction shutdown immediately after start; Engine overspeed during operation; Overspeed light on; Engine shuts down after running short time; LOP lamp comes on and engine stops running after about 12 seconds; OC (overcrank) lamp comes on and engine stops after running about 1 minute; Engine shutdown; Fault lamp illuminated; Overcrank diagnostic diode illuminated; Cranking circuit opens; Low oil pressure diagnostic diode illuminated; No diagnostic diodes illuminated (on standard control panels); High engine temperature diagnostic diode illuminated; Low engine temperature fault lamp illuminated; Engine malfunction shutdown; Engine does not overspeed during operation; Engine overspeeds during operation

Possible Causes

  • •Active shutdown fault (High Engine Temperature, Low Oil Pressure, Overcrank, or Overspeed)
  • •Bare wires grounding terminal TB11-40
  • •Battery connected incorrectly or abnormal voltage
  • •Defective Engine Monitor module J5
  • •Defective OS module 54
  • •Defective R-S-R switch S15
  • •Defective oil pressure sensor
  • •Defective starter
  • •Dirty K12 relay contacts or defective K12 relay
  • •Dirty K14 relay contacts or defective K14 relay
  • •Engine not pumping oil properly
  • •Engine speed reaches approximately 2100 r/min (overspeed condition)
  • •Failure to start after the 75-second cranking period
  • •Fault in Overspeed module
  • •Fault in Shutdown module
  • •Faulty Engine Monitor module J5
  • •Oil pressure drops to 14 psi (97 kPa)
  • •Open K12 ignition relay coil or dirty K12 relay socket connection
  • •Open-circuit starter coil or poor wiring between TB11 terminal 22 and starter
  • •Remote governor control set at High RPM position
  • •Start-Disconnect module J3 malfunction
  • •Throttle & governor linkage restricted movement

Suggested Actions

  1. 1Check for B+ at K13 terminal 3 to verify Start-Disconnect operation
  2. 2Check for defective OS module 54 or bare wires grounding terminal TB11-40
  3. 3Check fuse F1
  4. 4Check if ignition relay K12 energizes (See Test Procedure [A])
  5. 5Check or replace Engine Monitor module J5
  6. 6Check or replace Overspeed module
  7. 7Check or replace Shutdown module
  8. 8Check or replace Start-Disconnect module J3
  9. 9Check throttle & governor linkage for free movement
  10. 10Check wiring between TB11 terminal 22 and starter
  11. 11Clean K12 relay contacts or replace K12 relay
  12. 12Clean K14 relay contacts 1 h 7, check wiring, and replace K14 if necessary (See Test Procedure [D])
  13. 13Clean relay K12 socket connection
  14. 14Ensure remote governor control is not set at High RPM position
  15. 15Perform jumper test (jumper B+ at center terminal of R-S-R switch to terminal B of K12) and see Test Procedure [J]
  16. 16Reconnect wire
  17. 17Remove jumper and replace Engine Monitor module J5
  18. 18Remove lead from TB11-40 (P1-7 to overspeed module E3)
  19. 19Remove wire from terminal TB11-30 (P1-6 to S1) and reset
  20. 20Replace Engine Monitor module J5
  21. 21Replace defective R-S-R switch S15
  22. 22Replace lead to TB11-40 when engine is running
  23. 23Replace starter
  24. 24Reset and check if engine cranks when switched to Run
  25. 25Verify battery connection and voltage (See Test Procedure [B])

Related Onan Fault Codes

OVERSPEED LAMPOVERCRANK LAMPOVERCRANKO.S.O.C.LOW OIL PRESSURE LAMPLOW OIL PRESSURELOW ENGINE TEMPERATURELOPLETHIGH ENGINE TEMPERATURE LAMPHIGH ENGINE TEMPERATURE
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