P25C9 code meaning
Brake System Control Module B Requested MIL Illumination
Powertrain system Generic code P25xx codes Check engine light
What P25C9 means
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.
P25C9 at a glance
- Check engine lightYes, usually on
- Emissions testCan fail
- Limp modeNot expected
- Repair difficultyHard
- Typical labor0.5 to 3 hours
- Clears after repairWhen cleared with a scanner
Symptoms of P25C9
- Check engine lamp on
- Brake or stability warnings at the same time
Common causes of P25C9
- Most likelyFault stored in brake system control module B
- PossibleWeak battery or low system voltage
- Less likelyCommunication fault between module B and its partners
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Brake control module bCommunication bus
What each part of P25C9 means
| P | Powertrain system: engine, fuel system, ignition, emissions and transmission. |
| 2 | Generic code (second SAE range): it means the same on every make. |
| 5 | Area: vehicle speed, idle control and auxiliary inputs. |
| C9 | The exact fault in that area. |
What to do next
- Note P25C9 and any other codes stored with it: several codes together often point to one cause.
- Check for loose connectors and damaged wiring around the parts the code names.
- Check open recalls for your car: some faults are fixed for free by the dealer. Enter your VIN.
- Clear the code only after the repair. If it comes back, the fault is still there.
Buying a used car? Scan it for stored codes before you pay. A recently cleared memory can hide a problem.
Questions about P25C9
What does P25C9 mean?
P25C9 means "Brake System Control Module B Requested MIL Illumination". 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. It is a generic code, so it means the same on every make.
Is it safe to drive with P25C9?
Usually yes, for a short time, if the check engine light is steady and the car drives normally. If the light flashes or the car runs badly, stop and have it checked.
Will P25C9 fail an emissions test?
Yes, it can. P25C9 is emissions-related, so most inspection programs fail a car while it is stored or while the check engine light is on.
How hard is P25C9 to fix?
Difficulty: hard. A typical repair takes 0.5 to 3 hours of work. This is a job for a workshop.
Will P25C9 clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.