BMW fault CF2C - Brake pedal signal (engine management)
P1782 · Signal invalid
CF2C is set by the GS transmission control module when the brake pedal signal from the DME/DDE is invalid or missing. The transmission uses brake pedal status to manage creep behavior at standstill, prevent unintended engagement during braking, and coordinate hill-hold.
The GS module detected that the brake pedal status signal from the DME/DDE is absent or invalid. The warning severity is speed-dependent: ID 250 below 10 km/h (where brake input matters most for transmission control), ID 419 above 10 km/h. Monitoring requires 9-16V with terminal 30 on.
Safety warning
Loss of brake pedal signal can cause unexpected creep at standstill.
- Module
- GS
- Severity
- Warning
- Likely cause
- DME/DDE not receiving valid brake switch input
- Common fix
- Replacing the brake light switch or resolving DME/DDE fault
Symptoms
- Check engine light on after the second drive cycle.
- More prominent warning below 10 km/h where brake pedal input is critical for transmission control.
- Vehicle may creep unexpectedly at standstill if the transmission does not detect the brake.
- Hesitation or jerky behavior when transitioning from brake to throttle.
- Hill-hold may not engage or may disengage early.
Common causes
- DME/DDE not receiving valid brake switch input, preventing it from broadcasting brake status. The brake light switch sends the primary signal to the DME/DDE, which rebroadcasts it on CAN. A failed or misadjusted switch is the most common upstream root cause.
- DME/DDE fault preventing it from processing or rebroadcasting the brake switch input.
- Wiring damage between the brake light switch and DME/DDE. The connector at the brake pedal is in the driver's footwell and is exposed to moisture and physical contact.
- CAN bus fault (less likely unless other DME signals are also affected).
Diagnosis
- Read fault memory in the GS and DME/DDE with ISTA. If the DME/DDE has brake light switch faults, those are the upstream cause.
- Check basic brake light function: have someone observe the brake lights while you press the pedal. Lights that stay on, do not illuminate, or work intermittently point to the brake light switch.
- View DME/DDE live data for brake switch status. Press and release the pedal. The value should toggle cleanly between on and off with no delay or flickering.
- If the DME shows valid brake data but the GS does not receive it, inspect CAN wiring between the two modules.
- Inspect the brake light switch physically. It is mounted on a bracket near the top of the brake pedal arm. Check that it is seated in its retainer clip and that the plunger contacts the pedal lever cleanly. Check the connector for bent pins, corrosion, or loose fit.
Resolution
If the brake light switch is faulty, replace it. It is a common wear item and inexpensive. After replacement, verify proper seating in the retainer and clean pedal actuation. Clear faults in the GS and DME/DDE and test drive, paying attention to creep engagement and hill-hold function.