Chassis, generic

C0266 Active Brake Booster

Check engine lightUsually off
EmissionsNot relevant
Drive cycleNot required
Limp modePossible

Active brake booster faults are filed under C0266 by no maker, and the reachable J2012 lists omit the code. The number is a GM one: it shows up among PIP5094's keywords, and AA1Car words it exactly like C0265, EBCM Relay Circuit, so on GM vehicles it points to the relay that powers the ABS valves and pump rather than to a booster. The part in the title is a booster that builds pressure without the driver, either a vacuum unit with a solenoid or an electromechanical design such as Bosch's iBooster, whose motor works independently of engine vacuum and can brake on its own for assistance functions. On a vehicle with such a booster, its own maker-specific codes cover faults; with C0266, first find out which module stored it.

Likely causes

On GM vehicles fault in the brake module relay supply (fuse, contact, ground)
Faulty actuator or motor of an active booster
Damaged wiring or connector to the booster or relay

Symptoms

  • ABS or brake warning lamp on
  • Assistance functions such as automatic braking unavailable

Repair estimate

DifficultyHardWorkshop job
Parts and labour€30–1,800
Time0.5–4 h

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

Parts involved

ebcm relayactive brake boosterbrake control module

Related codes

C0265C0273C0595

References: static.nhtsa.gov, aa1car.com, bosch-mobility.com.