Onan Generator: “Fault 29”
warning RV generator fault codes
What it means
High battery voltage fault. The voltage across the genset's starting battery system was above roughly 19 volts — typically because the batteries got wired in series (24V) instead of parallel (12V), or a charger is boosting too hard.
Most likely causes
- 12V batteries serving the genset accidentally connected in series (24V) rather than parallel most likely
- Battery boost/charge rate set too high common
Safe checks you can do yourself
- Check the genset battery bank connections and confirm the 12V batteries are wired in parallel (12V), not in series (24V).
- Lower the battery boost charge rate if your charger offers that setting.
- Measure battery voltage with a meter; it should be near 12-14V, not approaching 19V+.
How to reset / clear Fault 29
- Correct the battery wiring or charge rate, then restart the generator from the control switch.
When to call a technician
If the wiring is confirmed correct and the charge rate is sensible but Code 29 persists.
Applies to
Marquis Gold · QG 4000 · QG 5500 · KY series · HGJAA · HGJAB · HGJAC · HGJAD · HGJAE · HGJAF
FAQ
What does Onan Generator code "Fault 29" mean?
High battery voltage fault. The voltage across the genset's starting battery system was above roughly 19 volts — typically because the batteries got wired in series (24V) instead of parallel (12V), or a charger is boosting too hard.
How do I reset Onan Generator Fault 29?
Correct the battery wiring or charge rate, then restart the generator from the control switch.
What is the most common cause of Fault 29 on a Onan Generator?
The most likely cause is 12v batteries serving the genset accidentally connected in series (24v) rather than parallel.
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Sources
- Onan Troubleshooting Codes (Service Manual Table 5) — High Battery Voltage Fault — Code No. 29 (>19 volts) (Cummins Onan (hosted by Heartland Owners))
Note: The ~19V threshold is per the cited service manual; exact trip point may vary slightly by control version.
● Last verified 2026-06-29 · compiled from manufacturer documentation. Codes can vary by model year — always cross-check your unit’s manual.