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.
Accuracy notes
The KY manual gives the threshold as 'greater than 19 volts'. The Quiet Diesel manual is tighter: above 19.2 V for 5 milliseconds during startup, or above 19.2 V for one second while running. The usual cause is the same either way — genset batteries wired in series for 24 V instead of parallel for 12 V, or a boost charge rate set too high.
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.
Related · Onan generator
Low cranking speed fault. During start the engine cranked slower than… Fault 12
Overvoltage fault. The controller could not keep the output voltage at…
Sources
- Onan Troubleshooting Codes (Service Manual Table 5) — High Battery Voltage Fault — Code No. 29 (>19 volts) (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