C066B code meaning
Right Rear Wheel Speed Sensor B Correlation
What C066B means
The second right rear speed value is electrically fine but disagrees with its references. No carmaker documents C066B or its limits. A Ford patent shows a check that suits a driven rear axle: the right rear speed is calculated as twice the output shaft speed divided by the axle ratio, minus the measured left rear speed. If measured and calculated values differ beyond a tolerance on consecutive passes or for more than 0.2 s, the fault is registered, and the calculated value stands in meanwhile. The tolerance can be tightened with lateral acceleration, and the side under more load gets the closer look. Bosch describes a similar estimate from the three other wheels, validated against the gearbox output. Wrong tire sizes or a damaged encoder can trigger such a mismatch.
C066B 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 C066B
- Warning after a fast or long drive
- Traction or stability functions temporarily reduced
Common causes of C066B
- Most likelyMismatched tire size or tread depth at the right rear
- PossibleEncoder with missing or extra pulses
- Less likelyAxle ratio or tire data in the module not matching the vehicle
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Rr wss bRr wssTone ring
What each part of C066B means
| C | Chassis system: brakes, ABS, steering and suspension. |
| 0 | Generic code: it means the same on every make (SAE standard). |
| 6B | The exact fault in that area. |
What to do next
- Note C066B 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 C066B
What does C066B mean?
C066B means "Right Rear Wheel Speed Sensor B Correlation". The second right rear speed value is electrically fine but disagrees with its references. It is a generic code, so it means the same on every make.
Is it safe to drive with C066B?
Drive gently and only to a workshop. With C066B the car can go into limp mode (reduced power) to protect itself.
Will C066B fail an emissions test?
C066B 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 C066B to fix?
Difficulty: medium. A typical repair takes 0.5 to 3 hours of work. This is a job for a workshop.
Will C066B 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.