Fault 24

Onan Generator: “Fault 24”

warning RV generator fault codes

Safety Until the sender works again the genset has no over-temperature protection. Do not run it hard with this fault outstanding. This is a fuel-burning engine. Never run it in an enclosed space or occupy the vehicle while it runs without a working carbon monoxide detector, and let hot parts cool before touching anything.

What it means

Faulty engine temperature sender. After ten minutes of normal running the controller checks the coolant temperature sender circuit, and it found the sender or its harness open. The engine is not necessarily overheating — the controller has simply lost its ability to tell.

Most likely causes

  1. Harness connector at the temperature sender disconnected or corroded most likely
  2. Broken wire between the control board and the sender common
  3. Failed temperature sender common

Safe checks you can do yourself

How to reset / clear Fault 24

  1. Reconnect anything found loose and run the set for more than ten minutes — the check only runs after that point.
  2. To re-display a logged code, press Stop three times within five seconds — the blinking times out after five minutes (fifteen on the HGJAA series). The controller keeps replaying the last fault even after the cause is gone; only a successful run clears it.

When to call a technician

The connector is sound and the fault repeats — the sender or the control board needs testing.

Accuracy notes

The same wire produces two different codes depending on how it fails. An open circuit is code 24; a lead touching ground is interpreted by the controller as genuine high temperature and comes out as code 1. A set that reports over-temperature while feeling cold is worth checking for a grounded sender lead before anyone drains the coolant.

Applies to

Onan Quiet Diesel HDKCA / HDKCB

FAQ

What does Onan Generator code "Fault 24" mean?

Faulty engine temperature sender. After ten minutes of normal running the controller checks the coolant temperature sender circuit, and it found the sender or its harness open. The engine is not necessarily overheating — the controller has simply lost its ability to tell.

How do I reset Onan Generator Fault 24?

Reconnect anything found loose and run the set for more than ten minutes — the check only runs after that point. To re-display a logged code, press Stop three times within five seconds — the blinking times out after five minutes (fifteen on the HGJAA series). The controller keeps replaying the last fault even after the cause is gone; only a successful run clears it.

What is the most common cause of Fault 24 on a Onan Generator?

The most likely cause is harness connector at the temperature sender disconnected or corroded.

Related · Onan generator

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Sources

● Checked against 1 manufacturer document · 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