Fault 15

Onan Generator: “Fault 15”

warning RV generator fault codes

Safety Draining the LPG system involves propane — do it outdoors, away from any flame or spark, with the generator off and cool. Propane is heavier than air and pools underneath the coach. Re-close the drain valve fully before restarting.

What it means

Underfrequency fault. The engine governor could not keep the engine spinning fast enough to maintain rated output frequency (Hz), so the controller shut the unit down.

Most likely causes

Excessive electrical load overworking the engine/governor (A/C plus chargers) most likely
On high-pressure LPG models: oil migrated from the supply system into the genset LPG plumbing, starving fuel common
Air cleaner restriction or a fuel-delivery problem limiting power less common

Safe checks you can do yourself

Reduce the number of connected appliances, especially air conditioners and active battery chargers, then restart.
On high-pressure LPG models only: with the system depressurized, drain accumulated oil from the genset LPG drain valve per the manual, then be sure to re-close the drain valve.
Check that the air cleaner is not clogged.

How to reset / clear Fault 15

Shed load and/or clear the LPG oil, then restart from the control switch.
Confirm the unit holds frequency under your normal load.

When to call a technician

If underfrequency continues after reducing load and (on LPG units) draining oil — the governor or fuel system likely needs a dealer.

Applies to

Marquis Gold · QG 4000 · QG 5500 · KY series · HGJAA · HGJAB · HGJAC · HGJAD · HGJAE · HGJAF

FAQ

What does Onan Generator code "Fault 15" mean?

Underfrequency fault. The engine governor could not keep the engine spinning fast enough to maintain rated output frequency (Hz), so the controller shut the unit down.

How do I reset Onan Generator Fault 15?

Shed load and/or clear the LPG oil, then restart from the control switch. Confirm the unit holds frequency under your normal load.

What is the most common cause of Fault 15 on a Onan Generator?

The most likely cause is excessive electrical load overworking the engine/governor (a/c plus chargers).

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Sources

Onan Troubleshooting Codes (Service Manual Table 5) — Underfrequency Fault — Code No. 15 (Cummins Onan (hosted by Heartland Owners))

Note: The LPG oil-drain step applies only to high-pressure LPG models; gasoline and low-pressure LPG units skip it.

● Last verified 2026-06-29 · compiled from manufacturer documentation. Codes can vary by model year — always cross-check your unit’s manual.