Brake Switch 'B' Circuit High
The Brake Switch 'B' circuit has detected a high voltage condition.
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What it means (plain English)
The brake switch is sending a signal that indicates the brakes are applied, but the voltage level is higher than expected, usually above 4.5 volts when the switch is on.
What the computer is actually seeing
The vehicle's control module sees an input voltage from the brake switch that exceeds 4.5 volts for too long when it should be toggling between 0 volts (off) and around 5 volts (on).
What a healthy reading looks like
Brake switch should see between 0 and 5 volts; when pressed, it should go to around 5 volts and drop to 0 volts when released.
Guided diagnostic — the DiagCoach way
Don't just throw parts at it. Walk through these in order — each step tells you whether to keep going or stop and fix what you found.
- 11. Inspect the brake switch connector and wiring harness for physical damage or corrosion. If damaged, repair or replace.
- 22. With the key in the ON position, use a multimeter to measure voltage at the brake switch - should be below 4.5 volts when the brake is not pressed. If it’s above, proceed to step 3.
- 33. Check the signal wire for shorts to voltage, tracing it back to the BCM. If there's a short, repair the wiring.
- 44. If no shorts are found, replace the brake switch and recheck the circuit.
Common causes
- Faulty brake switch
- Poor ground connection
- Wiring short to voltage
- Faulty Body Control Module (BCM)
Typical repair cost
$$$
Related codes
Frequently asked questions
Is it safe to drive with this code?
It's moderate; you should fix it soon but it’s typically drivable unless the brake lights are stuck on.
Will this code come back after repairs?
If all repairs are properly done and the circuit is fixed, the code should not return.
Why is this related to the BCM?
The BCM controls many functions including the brake light signals; a fault can affect multiple systems.
Working a real vehicle right now?
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