C0040: Brake Pedal Switch A — what it means, the affected system and what to check before replacing parts.
Meaning, symptoms, causes and checks
Brake Pedal Switch A. Basic catalogue definition; diagnostic details have not yet been reviewed.
Affected system: Chassis
Symptoms
- Illumination of the ABS warning light
- Activation of traction or stability control warning lamps
- Loss of anti-lock braking system functionality
- Potential wheel locking or skidding during emergency stops
Possible causes
- Faulty right front wheel speed sensor
- Damaged, corroded, or disconnected sensor circuit wiring
- Contaminated or physically damaged reluctor ring
- Internal failure of the wheel bearing magnetic encoder
- Malfunction of the ABS control module
What to check
- Scan the system for additional ABS-related diagnostic trouble codes
- Inspect the right front sensor wiring and connector for corrosion or physical damage
- Test the sensor electrical resistance using a multimeter according to factory specifications
- Monitor the live sensor signal with an oscilloscope while rotating the wheel manually
- Examine the reluctor ring or magnetic encoder for missing teeth, cracks, or debris
Also written as: C0040-00, C004000, CO040 (some scan tools add the fault-type byte, e.g. -00).