C066A Right Rear Wheel Speed Sensor B Intermittent/Erratic

C066A describes a second right rear speed signal that keeps dropping out or jumping. No carmaker documents it. Apart from loose contacts, the encoder deserves a close look. Schaeffler explains that many wheel bearings carry a multipole encoder just inside the seal: a ring magnetised in alternating poles that the sensor reads. NSK adds that this surface must not be pressed on during fitting and must be kept away from magnets and dirt. A ring with a cracked section, a spot of attracted metal swarf or a weakened pole produces a pulse train with gaps, which reads as an erratic speed rather than a dead channel. Such a ring cannot be repaired on its own when it is part of the bearing, so the bearing or hub has to be replaced.

Likely causes

Symptoms

• Warning appears and clears again during a drive
• Speed of the right rear wheel jumps in live data

Repair estimate

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

Parts involved

Related codes

References: schaeffler.com, nsk.com.