Onan Generator: “Fault 27”
warning RV generator fault codes
What it means
Voltage sense fault. The controller was unable to sense the generator's output voltage, so it shut down.
Most likely causes
- Internal voltage-sensing circuit or control fault most likely
- Wiring fault in the output-voltage sensing path common
Safe checks you can do yourself
- Confirm the code by reading the two-digit readout after the Code 3 service flash.
- Check that the generator's main breaker is set correctly and that obvious output connections are intact (generator off, battery negative disconnected).
How to reset / clear Fault 27
- This fault generally requires diagnosis by a dealer; there is no owner adjustment that clears the root cause.
When to call a technician
Whenever Code 27 appears — Onan directs this to an authorized dealer.
Applies to
Marquis Gold · QG 4000 · QG 5500 · KY series · HGJAA · HGJAB · HGJAC · HGJAD · HGJAE · HGJAF
FAQ
What does Onan Generator code "Fault 27" mean?
Voltage sense fault. The controller was unable to sense the generator's output voltage, so it shut down.
How do I reset Onan Generator Fault 27?
This fault generally requires diagnosis by a dealer; there is no owner adjustment that clears the root cause.
What is the most common cause of Fault 27 on a Onan Generator?
The most likely cause is internal voltage-sensing circuit or control fault.
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Sources
- Onan Troubleshooting Codes (Service Manual Table 5) — Voltage Sense Fault — Code No. 27 (Cummins Onan (hosted by Heartland Owners))
Note: Owner-facing forums sometimes report Code 27 clearing after fixing loose output/sense connections, but the manual lists it as dealer service.
● Last verified 2026-06-29 · compiled from manufacturer documentation. Codes can vary by model year — always cross-check your unit’s manual.