C05ACBrake Blending Separation Valve Stuck Closed
- Generic OBD-II code · Chassis
- Can trigger limp mode
- Needs a drive cycle to confirm a fix
- How the car detects it
- C05AC names one specific failure: the separation valve of the blended brake stays closed when it should open. Toyota's patent for a hybrid brake defines this closure failure and shows how it is pinned down: the control pressure sensor lags its target by more than a set amount for too long, the sensor passes its self-test and the upstream linear valve demonstrably delivers fluid, so the blockage must be the separation valve. The brake then drops into a no-current backup mode with master cylinder pressure on the front axle. Designs differ in how much a closed separation valve costs: Lucas showed a layout in which both front brakes still respond to the pedal although the isolating valve stays shut. No manufacturer publishes C05AC; assist and regeneration are typically suspended.
- What you may notice
- Brake warning, assist and regeneration off
- Higher pedal effort, longer stopping distance in backup mode
- Uneven braking between axles possible
- Likely causes
- LikelyValve armature stuck by contamination or corrosion
- PossibleOpen coil or wiring so a normally closed valve cannot open
- RareValve driver stage in the brake module defective
- Repair
- Workshop only · Usually a job for a workshop.Typical cost: €150 – €3,000
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.