OBD-II code · Powertrain (generic, extended)
P25B9 Auxiliary Ignition Switch On/Start Position Circuit High
Auxiliary ignition switch On/Start input reads stuck high — short to battery voltage. Wiring faults of this kind typically come from chafing, water ingress at connector seals, or pin push-back — a wiggle test on the harness while the code is active often confirms the location.
Is it safe to drive with P25B9?
Usually safe to drive in the short term. Get it diagnosed when convenient, sooner if the car drives differently.
Common causes
- Most likelyWire shorted to battery voltage
- Less likelyConnector pins corroded - high contact resistance
- Less likelySupply wire pinched against B+ source
Repair at a glance
- Difficulty
- Medium
- DIY friendly
- Best left to a mechanic
- Typical labour
- 0.5–2 h
- Emissions test
- Usually unaffected
- Parts involved
- Auxiliary Ignition Switch, Wiring Harness
Related codes
- P25B7Auxiliary Ignition Switch On/Start Position Circuit
- P25B6Turbocharger/Supercharger Wastegate B Stuck Closed
- P25B8Auxiliary Ignition Switch On/Start Position Circuit Low
- P25BARegeneration Control Switch Circuit/Open
- P25BBRegeneration Control Switch Circuit Low
- P25BCRegeneration Control Switch Circuit High
Code data: OBDex open dataset (CC0). Labour times are typical ranges, not a quote.