C066A code meaning
Right Rear Wheel Speed Sensor B Intermittent/Erratic
What C066A means
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.
C066A at a glance
- Check engine lightUsually not
- Emissions testNot an emissions code
- Limp modePossible
- Repair difficultyMedium
- Typical labor0.5 to 3 hours
- Clears after repairAfter a drive cycle
Symptoms of C066A
- Warning appears and clears again during a drive
- Speed of the right rear wheel jumps in live data
Common causes of C066A
- Most likelyEncoder ring with metal swarf, cracks or weakened poles
- PossibleIntermittent contact in plug or harness
- Less likelyWorn wheel bearing letting the encoder wobble
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Rr wss bTone ringSensor wiring
What each part of C066A means
| C | Chassis system: brakes, ABS, steering and suspension. |
| 0 | Generic code: it means the same on every make (SAE standard). |
| 6A | The exact fault in that area. |
What to do next
- Note C066A and any other codes stored with it: several codes together often point to one cause.
- Check for loose connectors and damaged wiring around the parts the code names.
- Check open recalls for your car: some faults are fixed for free by the dealer. Enter your VIN.
- Clear the code only after the repair. If it comes back, the fault is still there.
Buying a used car? Scan it for stored codes before you pay. A recently cleared memory can hide a problem.
Questions about C066A
What does C066A mean?
C066A means "Right Rear Wheel Speed Sensor B Intermittent/Erratic". C066A describes a second right rear speed signal that keeps dropping out or jumping. It is a generic code, so it means the same on every make.
Is it safe to drive with C066A?
Drive gently and only to a workshop. With C066A the car can go into limp mode (reduced power) to protect itself.
Will C066A fail an emissions test?
C066A is not an emissions code, so on its own it usually does not fail an emissions test. Other stored codes or a lit check engine light still can.
How hard is C066A to fix?
Difficulty: medium. A typical repair takes 0.5 to 3 hours of work. This is a job for a workshop.
Will C066A clear itself after the repair?
After the repair the car has to complete a drive cycle (a mix of city and highway driving) before the test runs again. Until then the readiness monitor shows "not ready", which can fail an inspection.