Here's a cheat sheet I have for common faults:
Onan common fault Codes Cheat Sheet
• Two blinks indicates a low oil pressure fault.
• Three blinks indicates a service fault.
Press Stop once to cause the two-digit, second level fault code to blink.
(Pressing Stop again will stop the blinking.)
The two-digit code consists of 1, 2, 3, 4 or 5 blinks, a brief pause, and then 1 to 9 blinks.
The first set of blinks represents the tens digit
and the second set of blinks the units digit of the fault code number.
For example, Fault Code No. 36 appears as:
blink-blink-blink—pause—blink-blink-blink-blink-blink-blink— long pause—repeat
• Four blinks indicates that cranking
exceeded 30 seconds without the engine
starting.
Restoring Fault Code Blinking – The fault code stops blinking after five minutes
(15 minutes, Series HGJAA).
Press Stop three times within five seconds to restore blinking.
Note that the last fault logged will blink, even after the condition that
caused the shutdown has been corrected.
TABLE 5. TROUBLESHOOTING
LOW OIL PRESSURE FAULT—CODE NO. 2
(First-level fault code—Low oil pressure cutoff switch did not open)
SERVICE CHECK FAULT—CODE NO. 3
(First-level fault code—Indicates fault with second-level fault code)
Corrective Action: 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.
OVERCRANK FAULT—CODE NO. 4
(First-level fault code—Cranking exceeded 30 seconds without engine starting)
LOW OIL PRESSURE CUTOFF SWITCH FAULT—CODE NO. 23
(Controller sensed switch still open during start—not a running fault)
ENGINE STOPPED FAULT—CODE NO. 36
(Engine stopped without command by controller)
OVERPRIME FAULT—CODE NO. 57
(Prime mode exceeded 3 minutes)
