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DTC codes / C00xx · Brakes, steering and suspension / C0090

C0090Hydraulic Brake Pressure Sensor Circuit

C0090 indicates that the antilock braking system (ABS) control module has detected an electrical fault in the circuit for the hydraulic brake pressure sensor, which monitors the pressure in the brake hydraulic system. The computer compares the sensor signal voltage against expected values and sets this code when the signal is out of range, erratic, or missing entirely.

SystemChassis
Code typeGeneric (all makes)
SeverityMedium
Fix difficultyIntermediate
AreaBrakes, steering and suspension

Symptoms you may notice

  • The ABS warning light illuminates on the dashboard.
  • The traction control or stability control warning light may also turn on.
  • The ABS system may be disabled, though normal braking usually remains functional.
  • A soft or spongy brake pedal feel if the sensor is reading incorrectly.
  • Often no symptoms besides the warning light, especially if the sensor signal is only intermittently faulty.

Common causes, most likely first

  1. Faulty hydraulic brake pressure sensor.
  2. Damaged or corroded wiring or connector at the sensor.
  3. Open or short circuit in the sensor wiring harness.
  4. Contaminated or degraded brake fluid affecting sensor operation.
  5. Failed ABS control module (less common).
  6. Air trapped in the hydraulic system causing pressure readings to be out of range.

How to diagnose and fix it

  1. Inspect the sensor connector and wiring for corrosion, damage, or loose pins.
  2. Check brake fluid level and condition; top off or replace if contaminated.
  3. Use a scan tool to read live data from the hydraulic brake pressure sensor and compare to expected values.
  4. Perform a voltage drop test on the sensor circuit to check for excessive resistance.
  5. Bleed the brake system to remove air that could cause incorrect pressure readings.
  6. Replace the hydraulic brake pressure sensor if testing confirms it is faulty.
  7. Clear the code and verify the repair with a test drive and re-scan.

What most technicians overlook on C0090

  • A weak battery or charging system issue can cause the ABS module to set false pressure sensor codes, so always check battery voltage and ground connections first.
  • The hydraulic brake pressure sensor is sometimes integrated into the ABS pump assembly, making replacement more involved than a simple sensor swap.
  • Brake fluid that has absorbed moisture can cause the sensor to read incorrectly, so a fluid flush is sometimes the only repair needed.
  • The code may be stored due to a momentary glitch and not return after clearing; always test-drive before condemning parts.

Can I keep driving with C0090?

The vehicle is generally safe to drive with the ABS light on because normal braking remains, but avoid hard braking or slippery conditions where ABS is needed. Have the system diagnosed soon to restore full ABS function.

Tools that help

Tools we recommend are in the Auto Veteran shop on Amazon. As an Amazon Associate we earn from qualifying purchases.

Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.

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