Chassis, generic

C05AC Brake Blending Separation Valve Stuck Closed

Check engine lightUsually off
EmissionsNot relevant
Drive cycleRequired
Limp modePossible

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.

Likely causes

Valve armature stuck by contamination or corrosion
Open coil or wiring so a normally closed valve cannot open
Valve driver stage in the brake module defective

Symptoms

  • Brake warning, assist and regeneration off
  • Higher pedal effort, longer stopping distance in backup mode
  • Uneven braking between axles possible

Repair estimate

DifficultyShop_onlyWorkshop job
Parts and labour€150–3,000
Time1–4 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

brake blending valve

Related codes

C05ABC05ADC0024

References: patents.google.com, patents.google.com, patents.google.com.