Onan Generator: “Fault 2 (Low Oil)”
danger RV generator fault codes
What it means
Low oil pressure — a first-level fault shown as two blinks. The Quiet Diesel manual defines it precisely: oil pressure dropped below 14 psi for three seconds during normal operation. The controller shuts the engine down rather than let it run without pressure.
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.
- If the dipstick reads above Full, drain the excess: too much oil lets the crankshaft whip it into foam, and a pump cannot pump foam.
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.
Accuracy notes
Two blinks is a first-level fault on liquid-cooled Quiet Diesel sets. The air-cooled KY and KYD operator manuals document only three and four blinks at that level, so on a gasoline or LPG set a count of two is usually a miscount — watch a full cycle and find the long pause. Do not read two blinks as second-level code 22 either; codes 33 and 44 are unassigned precisely so first-level and second-level counts cannot collide.
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 — a first-level fault shown as two blinks. The Quiet Diesel manual defines it precisely: oil pressure dropped below 14 psi for three seconds during normal operation. The controller shuts the engine down rather than let it run without pressure.
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.
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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))
- Operator Manual — RV Generator Set HDKCA / HDKCB (Spec A–E) — 0981-0173 (Issue 10), Section 4 Troubleshooting, Table 4-1 (Cummins Inc. (Onan Quiet Diesel))
● Checked against 2 manufacturer documents · Last verified 2026-08-07 · compiled from manufacturer documentation. Codes can vary by model year — always cross-check your unit’s manual. How we verify