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.
Accuracy notes
The Quiet Diesel manual is specific about when the controller decides this: AC sensing was lost while the field was working normally and frequency was at least 40 Hz — so the engine was running fine and only the sensing path failed. That is why it points at the voltage sense transformer and its wiring rather than at the engine.
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.
Related · Onan generator
Overvoltage fault. The controller could not keep the output voltage at… Fault 13
Undervoltage fault. The controller could not hold the generator's AC…
Sources
- Onan Troubleshooting Codes (Service Manual Table 5) — Voltage Sense Fault — Code No. 27 (Cummins Onan (hosted by Heartland Owners))
- Operator Manual — RV Generator Set KY (Spec J–N) — 981-0159 (Issue 9), Section 4 Troubleshooting, Table 2 (Cummins Inc. (Onan))
- 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 3 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