Brake Switch Fault
The brake switch is malfunctioning or sending an incorrect signal.
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)
Inside the truck's control unit, the brake switch is supposed to send a signal between 0 to 5 volts when the brake pedal is pressed. If it sends a signal that's too high or low, or if it doesn’t signal at all, the system throws this code.
What the computer is actually seeing
The control module expects a signal between 0.1V (off) and 4.5V (on) from the brake switch. If it sees a voltage outside this range, it triggers the fault code.
What a healthy reading looks like
0.1V (brake off) to 4.5V (brake pressed) from the brake switch.
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 wiring and connectors at the brake switch for damage or corrosion. If damaged, repair or replace as needed. Decision Point: If wiring/connectors are good, proceed to step 2. If damaged, fix before testing further.
- 22. Check the brake switch operation by measuring the voltage at the switch with the brake pedal pressed and released. Expected voltage: 0.1V (off), 4.5V (on). Decision Point: If voltages are out of range, replace the brake switch. If voltages are correct, proceed to step 3.
- 33. Inspect the ABS module and its connections for faults or moisture. Decision Point: If found faulty, replace the ABS module; if in good condition, further diagnostics are needed. Loop back to step 1 if more symptoms are present.
Common causes
- Faulty brake switch
- Wiring issues or shorts in brake switch circuit
- Bad connector at the brake switch
- Faulty ABS module affecting brake signal
Typical repair cost
$$
Related codes
Frequently asked questions
Is it safe to drive with this code?
It's moderate severity; you can drive but should fix it soon to ensure braking systems function properly.
Will this code come back after clearing?
If the underlying issue isn’t fixed, yes, the code is likely to return.
Why does this code pair with SPN 156?
SPN 156 also involves braking system faults, indicating related issues in brake control signaling.
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