OBD-II code · Powertrain (generic, extended)
P25C9 Brake System Control Module B Requested MIL Illumination
A second brake system control module (typically the redundant secondary unit on by-wire or AV-grade brake systems) has signalled an emissions-relevant fault and requested the engine controller to switch on the MIL.
Is it safe to drive with P25C9?
Usually safe to drive in the short term. Get it diagnosed when convenient, sooner if the car drives differently.
Common causes
- Most likelyActive DTC stored in the secondary brake module
- Less likelyCommunication loss interpreted as MIL request
Repair at a glance
- Difficulty
- Medium
- DIY friendly
- Best left to a mechanic
- Typical labour
- 0.5–2.5 h
- Emissions test
- Usually unaffected
- Parts involved
- Brake Control Module B, Communication Bus
Related codes
- P25A2Brake System Control Module A Requested MIL Illumination
- P25C6Brake Booster Temperature Sensor A Circuit Low
- P25C7Brake Booster Temperature Sensor A Circuit High
- P25C8Brake Booster Temperature Sensor A Circuit Intermittent/Erratic
- P25CAIntake Camshaft Actuator Park Lock Control Circuit / Open Bank 1
- P25CBIntake Camshaft Actuator Park Lock Control Circuit Low Bank 1
- P25CCIntake Camshaft Actuator Park Lock Control Circuit High Bank 1
Code data: OBDex open dataset (CC0). Labour times are typical ranges, not a quote.