What it means
This code identifies a fault associated with brake pedal switch A. The specific failure depends on the diagnostic subtype.
How it works
The brake control module monitors brake pedal switch A to detect pedal application, which can affect braking functions and cruise control. C0040 identifies a subfault associated with switch A; the accompanying diagnostic subtype indicates the specific problem, such as a switch, adjustment, wiring, fuse, or module fault.
Common causes
Most likely first.
- Faulty brake pedal switch
- Misadjusted switch
- Damaged wiring or connector
- Blown fuse
- Brake control module fault
Symptoms
- Brake lights fail or stay on
- Cruise control may not work
- ABS or brake warning light
How to diagnose it
- Read C0040's accompanying subfault details with an ABS-capable scan tool, then check whether brake lights turn on and off correctly as the pedal is pressed and released.
- Inspect brake pedal switch A and its connector for looseness, damage, or misalignment that could prevent reliable pedal detection.
- Check the switch A wiring and relevant fuse for an open, short, or loss of supply indicated by the subfault, comparing results with the manufacturer's specification.
- Monitor switch A status on a scan tool while operating the pedal to see whether the module registers each press and release consistently.
- If the switch, adjustment, wiring, and fuse check out, test the brake control module using the vehicle's diagnostic procedure.
Common fixes
- Adjust brake pedal switch A if it is misaligned and the manufacturer's procedure allows adjustment.
- Reconnect or repair a damaged switch A connector or wiring.
- Replace a faulty brake pedal switch A after confirming it fails the prescribed checks.
- Replace a blown relevant fuse after identifying and correcting the cause.
- Repair a brake control module fault only if switch circuit tests pass.
Can I keep driving?
Do not drive if the brake lights fail, stay on, or the brake pedal behavior is abnormal; other drivers may not see your braking, and cruise control may not disengage as expected. If brake lights work normally and braking is normal, drive cautiously to arrange prompt repair.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.