BMW fault CF18 - Accelerator pedal signal
U112E · Lost communication
CF18 is set by the GS transmission control module when it loses the accelerator pedal position signal from the DME/DDE. The transmission uses pedal position to anticipate driver intent and adjust shift timing and gear selection accordingly.
The GS module has lost the CAN message carrying pedal position data. The DME/DDE reads the pedal sensor directly and broadcasts the position to other modules. Monitoring requires 9-16V battery voltage with terminal 30 on.
- Module
- GS
- Severity
- Warning
- Likely cause
- DME/DDE fault or pedal sensor failure
- Common fix
- Resolving the DME/DDE or pedal sensor fault
Symptoms
- Check engine light on after the second drive cycle.
- CC-ID 419 (transmission warning) displayed.
- Sluggish or unpredictable shift behavior as the transmission cannot anticipate throttle input.
- Delayed or inappropriate upshifts during acceleration.
- Hesitation during kickdown requests.
Common causes
- DME/DDE fault affecting its pedal sensor reading or CAN broadcast. The DME/DDE is the source of this signal.
- Accelerator pedal sensor failure or intermittent connection. The DME/DDE cannot broadcast data it is not receiving.
- Wiring damage between the pedal sensor and DME/DDE, or between the DME/DDE and the CAN bus. The pedal connector in the driver's footwell is susceptible to moisture or physical damage.
- Broader CAN bus fault preventing the message from reaching the GS module.
Diagnosis
- Read fault memory in the GS and DME/DDE with ISTA. If multiple modules report communication faults, the issue is likely a CAN bus problem. If only the GS reports this, focus on the DME/DDE and pedal sensor.
- Check the DME/DDE for accelerator pedal sensor faults. If present, those are the upstream cause.
- View DME/DDE live data for pedal position. With ignition on, slowly press the pedal from rest to full travel. The value should sweep smoothly from 0% to 100% with no dropouts or dead spots.
- If the DME shows valid pedal data but the GS does not receive it, inspect CAN wiring between the two modules.
- If the DME shows invalid pedal data, inspect the pedal sensor connector in the driver's footwell for corrosion, bent pins, and secure seating. Check the wiring from the pedal to the DME for chafing or breaks.
Resolution
Resolve the upstream DME/DDE or pedal sensor fault first. If the pedal sensor has failed, replace the pedal assembly (on most platforms this is a complete unit including the sensor). If CAN wiring is damaged, repair the harness. Clear all faults and test drive to confirm normal shift behavior.