Brake Switch Input Circuit Failure
The brake switch is malfunctioning or has an open circuit.
Heads up: this code wasn't in our hand-written library yet, so DiagCoach AI built this page on the fly. Double-check critical specs against service info before condemning parts.
What it means (plain English)
The brake switch tells the computer when the brake pedal is pressed. If it's not working right, the computer might not know when to control the brakes, causing safety issues.
What the computer is actually seeing
The computer monitors the brake switch input voltage. It expects a voltage of 0V when the switch is off (brake not pressed) and approximately 5V when on (brake pressed).
What a healthy reading looks like
0V (brake off), 5V (brake pressed)
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.
- 1Check the condition of the brake fluid level and brake system integrity.
- 2Inspect wiring and connectors for frays, corrosion, or looseness.
- 3Test the brake switch: unplug it and measure voltage at the harness while activating the pedal. You're looking for 0V when off and about 5V when pressed. If the voltage is outside these specs, the switch is bad.
- 4If the switch tests okay, trace the wiring back to the ECM. Check for any shorts or opens in the circuit that could prevent the correct signal from reaching the computer.
- 5Reconnector any loose connections and clear the code to see if it returns.
Common causes
- Faulty brake switch
- Wiring issues to the brake switch
- Corroded or loose connectors
- Poor ground connections
Typical repair cost
$$
Related codes
Frequently asked questions
Is it safe to drive with this code active?
It's not recommended to drive as the brake system may not function properly, risking safety.
Will this code come back after clearing it?
If the underlying issue isn't fixed, it will likely return.
Why does this code pair with SPN 478?
SPN 478 indicates an issue with the brake pedal position, which can be directly related to the brake switch failure.
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