C0594Brake Booster Motor A Performance
- Generic OBD-II code · Chassis
- Turns on the check-engine light
- Can trigger limp mode
- How the car detects it
- C0594 judges whether booster motor A moves as commanded, not its wiring. GM's 2016/2019 hybrid booster flags a motor turning against the commanded direction (under 15 rad/s while more than 25 rad/s is requested), more than seven direction reversals, oscillation with the brake applied, or unintended backward rotation above 40 rad/s. In the XT4 unit and the 2023/2025 EBCM tables the plunger must reach its end position at start-up; the code also sets if the motor test finds a hardware fault, if pressure sensor 2 stays at or below 10 bar while the motor moves, or if modelled and measured pressure differ by over 40 bar for 0.2 s. All Type A with MIL. Mitsubishi files C18E1-49 (motor not operating normally) of the Outlander PHEV as C0594 with MIL.
- What you may notice
- Loss of brake assist with a heavy pedal
- Check engine and brake warning lamps on
- Booster noise or pedal vibration before the fault sets
- Likely causes
- LikelyBinding gear, spindle or plunger inside the booster
- PossibleWorn or damaged booster motor A
- PossibleAir or leakage in the hydraulic circuit so pressure does not follow motor travel
- RareFaulty rotor position feedback causing wrong direction or oscillation
- Repair
- Workshop only · Usually a job for a workshop.Typical cost: €250 – €3,000
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.