Onan Generator: “Fault 2 (Low Oil)”
danger RV generator fault codes
What it means
Low oil pressure fault (a first-level fault shown as two blinks, code 2). The low-oil-pressure cutoff switch did not stay closed, so the controller shut the engine down to protect it. This is one of the most common reasons an Onan starts then dies.
Most likely causes
- Engine oil level low most likely
- Operating on a steep slope so the pickup is uncovered common
- Overfilled oil (above the Full mark) causing aeration less common
- Faulty oil-pressure cutoff switch or actual low oil pressure less common
Safe checks you can do yourself
- With the engine off and cool and the RV reasonably level, check the dipstick and add oil to the Full mark if low.
- If overfilled above the Full mark, drain the excess.
- Make sure the RV is roughly level when running the genset.
How to reset / clear Fault 2 (Low Oil)
- Correct the oil level first, then restart.
- The fault is logged; press Stop three times within 5 seconds to re-display it. It clears on the next successful run cycle.
- Note: code 2 (and code 3 and 4) are FIRST-level codes - do not misread two blinks as a second-level code 22, three as 33, or four as 44.
When to call a technician
Oil level is correct and the RV is level but code 2 keeps shutting the unit down (possible faulty cutoff switch or real low oil pressure) - see an authorized Onan dealer.
Applies to
Onan RV QG / KY series RV gensets · Onan blink-code-controller RV gensets
FAQ
What does Onan Generator code "Fault 2 (Low Oil)" mean?
Low oil pressure fault (a first-level fault shown as two blinks, code 2). The low-oil-pressure cutoff switch did not stay closed, so the controller shut the engine down to protect it. This is one of the most common reasons an Onan starts then dies.
How do I reset Onan Generator Fault 2 (Low Oil)?
Correct the oil level first, then restart. The fault is logged; press Stop three times within 5 seconds to re-display it. It clears on the next successful run cycle. Note: code 2 (and code 3 and 4) are FIRST-level codes - do not misread two blinks as a second-level code 22, three as 33, or four as 44.
What is the most common cause of Fault 2 (Low Oil) on a Onan Generator?
The most likely cause is engine oil level low.
Related · Onan generator
First-level 'service check' fault. Three blinks tell you the… Fault 12
Overvoltage fault. The controller could not keep the output … Fault 13
Undervoltage fault. The controller could not hold the genera… Fault 14
Overfrequency fault. The engine governor could not hold the … Fault 15
Underfrequency fault. The engine governor could not keep the… Fault 19
Governor actuator fault. The controller detected an open or …
Sources
- Onan RV Generator Troubleshooting Codes (Table 5) — TABLE 5 - LOW OIL PRESSURE FAULT-CODE NO. 2 (first-level; cutoff switch did not open) (Cummins/Onan (hosted by Heartland Owners))
Note: Code 2 is a first-level (single-tier) fault shown as a steady repeating 2-blink, distinct from the two-digit second-level service codes that follow a 3-blink 'service' indication.
● Last verified 2026-06-29 · compiled from manufacturer documentation. Codes can vary by model year — always cross-check your unit’s manual.