Chassis, generic

C0666 Right Rear Wheel Speed Sensor B Circuit/Open

Check engine lightUsually off
EmissionsNot relevant
Drive cycleNot required
Limp modePossible

The second speed channel at the right rear wheel is open: a wire, terminal or the sensor itself no longer conducts. C0666 is not documented by any carmaker. Where the repair ends depends on the hub design. Schaeffler's wheel bearing brochure notes that some third-generation bearings carry all speed sensors inside the bearing unit, so an internal open there can mean replacing the whole hub assembly. The loss also affects the parking brake. A ZF patent on electric parking brakes handles a missing or implausible speed signal by closing the brake only while the switch is held and with a steady rise in force, so the car stays stable; full clamping follows only once maximum force is reached. Normal ABS often stays available through sensor A.

Likely causes

Harness or connector open at the right rear wheel
Sensor inside the hub bearing unit failed open
Input stage for channel B in the brake module defective

Symptoms

  • Warning for brake or stability system on every start
  • Electric parking brake may only apply gradually while the switch is held

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€60–600
Time0.5–2.5 h

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

Parts involved

rr wss bsensor wiring

Related codes

C0667C0668C0669C066AC0512C065F

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