ABS and brakes

C0090 — Right Rear ABS Solenoid #1 Circuit Malfunction

Severity: medium Drive with care, to a shop

What C0090 means

The ABS control module uses solenoid valves in the hydraulic unit to modulate brake pressure at each wheel during hard braking. C0090 is set when the module sees an open, short or out-of-range current or resistance in the right rear solenoid #1 circuit. The module then usually disables ABS and related stability functions.

Symptoms

  • ABS warning light on
  • Traction or stability control light on
  • Rear wheel locking under hard or slippery-surface braking
  • Pulsating or unusual brake pedal feel
  • Intermittent stability control faults

Possible causes

  1. Failed right rear ABS solenoid #1 (coil or hydraulic unit)
  2. Damaged wiring or connector in the solenoid circuit (open, short, corrosion)
  3. Poor power supply or ground to the circuit
  4. Faulty ABS control module (EBCM)
  5. Rarely, a wheel speed sensor problem causing a related ABS fault

How to diagnose

  1. Scan all modules, review freeze frame data, clear the code and see if it returns
  2. Check brake fluid level and condition
  3. Inspect the hydraulic unit connector and harness for corrosion, moisture, chafing or past repairs
  4. Check ABS fuses and relays, and verify power and ground at the module
  5. Measure solenoid coil resistance and compare with the manufacturer spec
  6. Test wiring between the module and solenoid for opens and shorts to ground or voltage
  7. Run the scan tool's active valve test if available
  8. If wiring and solenoid test good, suspect the ABS module

Common fixes

  • Repair damaged wiring or replace the connector
  • Clean terminals and restore power and ground to the module
  • Replace the solenoid or the hydraulic unit assembly (valves are often not sold separately)
  • Repair or replace the ABS module, then program it and bleed the brakes

Questions and answers

Can I drive with a C0090 code?

Usually yes, since the base brake system typically still works, but ABS and stability control may be off. Drive carefully and don't put off diagnosis.

What most often causes C0090?

A failed solenoid in the hydraulic unit or damaged wiring and connectors are the usual culprits. Inspect the harness, check power and ground, then measure the solenoid resistance.

This is general information about the code. The meaning can differ between makes and models: a scan tool and the repair manual for your car will show the exact cause.