Brake Switch A Circuit

What it means

The engine computer has detected an implausible signal from the brake pedal switch. The computer uses this signal to cancel cruise control and release the transmission park lock, and the rear brake lights also depend on it.

Related codes: P0500P0850

Symptoms5

• Cruise control does not work.
• Brake lights do not come on, or stay on all the time.
• Shifter hard to move out of Park on some vehicles.
• Push-button start may not crank on some vehicles because the computer does not see the brake pressed.
• Check engine light on.

Possible causes6

• Misadjusted or failed brake switch.
• Worn or missing rubber or plastic stop pad that the switch presses against at the pedal.
• Blown brake light fuse.
• Open or shorted switch wiring.
• Loose or corroded connector.
• Disagreement between the two switch circuits on vehicles that use a dual-circuit switch.

How to diagnose5

1. Check that the rear brake lights come on when the pedal is pressed and go off when released.
2. Watch the brake switch status on a scan tool while pressing and releasing; it should change immediately.
3. Check the brake light fuse.
4. Inspect the switch position at the pedal and the stop pad it rests on.
5. Measure switch continuity and voltage at the connector and compare with the manufacturer specification.

How to fix5

1. Replace a blown fuse after making sure there is no short.
2. Adjust the brake switch or replace the missing stop pad.
3. Repair the wiring or connector.
4. Replace the brake switch.
5. Clear the codes and confirm the brake lights and cruise control work.

Repair cost

In Saudi riyals; the highlighted part is the expected range for this fault.

The cost is usually low because the fix is a fuse, an adjustment or an inexpensive switch; it rises a little if the wiring needs repair.

Prices are rough estimates for common cars at independent workshops and vary with the car and the source of the part.
Prices last updated: September 2026

Frequently asked questions