P25C9Brake System Control Module B Requested MIL Illumination
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- How the car detects it
- P25C9 tells the engine module that a second brake system control module, labelled B, has found an emission-relevant malfunction and wants the check engine lamp switched on. GM uses the code in its hybrid OBD tables 16OBDG01, 18OBDG01 and 19OBDG01: the engine module listens to the lamp request message from module B continuously, starting three seconds after power-up, and logs P25C9 as Type A but without its own lamp request, since the brake module already asks for the lamp. Which fault lies behind it only module B can say, so its memory is read first; a low battery or network trouble can also upset it. Brake module A reports the same situation as P25A2. As braking functions may be involved, the car should be checked soon.
- What you may notice
- Check engine lamp on
- Brake or stability warnings at the same time
- Likely causes
- LikelyFault stored in brake system control module B
- PossibleWeak battery or low system voltage
- RareCommunication fault between module B and its partners
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Hard · Usually a job for a workshop.Typical cost: €50 – €1,500
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.