Fault 4

Onan Generator: “Fault 4”

warning RV generator fault codes

Safety 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

Overcrank — a first-level fault shown as four blinks. The starter turned the engine and it never caught, so the controller stopped cranking to protect the starter. It is a fuel, spark or cranking-speed problem, not a controller problem.

Most likely causes

  1. Out of fuel — on a shared tank the genset pickup tube sits higher than the vehicle engine pickup, so the generator runs dry while the dash gauge still shows fuel most likely
  2. Fuel system needs priming after running dry or standing most likely
  3. LPG container low, or too cold to vaporise fast enough to meet demand common
  4. Spark plug worn or its lead not seated (gasoline and LPG sets) common
  5. Air cleaner clogged common
  6. Cranking too slow to fire — weak battery, poor connections, or oil too thick for the temperature common
  7. Glow plugs not heating (diesel sets) less common
  8. Fuel pump, fuel filter or an air leak in the fuel line less common
  9. Governor actuator not pulling in its plunger, so the engine cannot start at all (diesel sets) rare

Safe checks you can do yourself

How to reset / clear Fault 4

  1. Correct the cause, then start again. Do not crank for more than 30 seconds at a time — Cummins warns that excessive cranking overheats and damages the starter motor.
  2. Let the starter cool between attempts.
  3. 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

Fuel, spark, air and battery all check out and it still will not fire — the fuel pump, injectors, glow plugs or the governor actuator need testing.

Accuracy notes

Cummins does not give one consistent cranking limit for this code. The KY operator manual says '15 to 20 seconds' in its introduction and 'exceeded 20 seconds' in its own troubleshooting table in the same document; the 2019 RV Generator Handbook says 30 seconds; the HDKCA/HDKCB diesel manual says 35 seconds. Any page quoting a single figure as 'the' Onan overcrank threshold has copied one table without checking the others. The number does not change the diagnosis.

Applies to

Onan RV QG / KY series (gasoline and LPG) · Onan KYD · Onan Quiet Diesel HDKCA / HDKCB

FAQ

What does Onan Generator code "Fault 4" mean?

Overcrank — a first-level fault shown as four blinks. The starter turned the engine and it never caught, so the controller stopped cranking to protect the starter. It is a fuel, spark or cranking-speed problem, not a controller problem.

How do I reset Onan Generator Fault 4?

Correct the cause, then start again. Do not crank for more than 30 seconds at a time — Cummins warns that excessive cranking overheats and damages the starter motor. Let the starter cool between attempts. 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 4 on a Onan Generator?

The most likely cause is out of fuel — on a shared tank the genset pickup tube sits higher than the vehicle engine pickup, so the generator runs dry while the dash gauge still shows fuel.

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Sources

● 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