Brake System Pressure Sensor Signal Invalid
The brake system pressure sensor is sending invalid data to the control module.
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 pressure sensor measures how hard you're pushing the brake pedal. If it sends incorrect readings, the computer can't adjust brake performance properly.
What the computer is actually seeing
The brake control module expects to see a voltage signal from the pressure sensor that corresponds to the brake fluid pressure. Under normal operation, this voltage should range between 0.5V and 4.5V depending on the pressure applied.
What a healthy reading looks like
Expected sensor voltage is 0.5V (no pressure) to approx 4.5V (full pressure).
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. Check brake fluid level. Ensure it's between the minimum and maximum marks. If low, top it up and see if the code clears.
- 22. Inspect the wiring and connectors to the brake pressure sensor for any signs of damage or corrosion. Repair any issues found and retest.
- 33. Measure the voltage output from the brake pressure sensor with a multimeter while someone presses the brake. It should range from 0.5V to 4.5V. If it's outside this range, replace the sensor.
- 44. If the sensor tests good, check the brake control module for fault codes or issues. If necessary, replace the control module.
Common causes
- Faulty brake pressure sensor
- Damaged wiring to the brake pressure sensor
- Faulty brake control module
- Low brake fluid level
Typical repair cost
$$
Related codes
Frequently asked questions
Is it safe to drive with this code active?
Yes, but be cautious. You'll have reduced braking performance and should get it fixed soon.
Will this issue come back after clearing the code?
If the underlying problem isn't fixed, the code will likely return.
Why does this code sometimes pair with C121B?
C121B indicates a similar issue with the brake pedal position or additional brake system faults that may occur concurrently.
Working a real vehicle right now?
Let DiagCoach walk you through it live with your specific symptoms, vehicle, and what you've already checked.
Start guided diagnostic →