C0664 code meaning
Left Rear Wheel Speed Sensor B Correlation
What C0664 means
C0664 flags that the second left rear speed value disagrees with its reference speeds, although its circuit is sound. No carmaker publishes the comparison. Two patents show how a rear wheel can be cross-checked. Bosch uses the left rear wheel as its example of a failed or omitted sensor: the module estimates that wheel from the other three, for instance as the front average or as front left plus front right minus rear right, and checks the result against the gearbox output speed. A fault counts only when the deviation stays above a threshold for a set time. Ford relies on the differential: the mean of both rear wheels follows from the output shaft speed and the final drive ratio. A sensor that disagrees with such references gets flagged even though it still sends pulses.
C0664 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 C0664
- Warning set after a longer drive, not at start
- Automated or redundant brake functions refused
Common causes of C0664
- Most likelyDamaged or wrong encoder ring giving a false pulse count
- PossibleTire of different size or heavily worn on the left rear
- Less likelySensor B losing pulses at high speed
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Lr wss bLr wssTone ring
What each part of C0664 means
| C | Chassis system: brakes, ABS, steering and suspension. |
| 0 | Generic code: it means the same on every make (SAE standard). |
| 64 | The exact fault in that area. |
What to do next
- Note C0664 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 C0664
What does C0664 mean?
C0664 means "Left Rear Wheel Speed Sensor B Correlation". C0664 flags that the second left rear speed value disagrees with its reference speeds, although its circuit is sound. It is a generic code, so it means the same on every make.
Is it safe to drive with C0664?
Drive gently and only to a workshop. With C0664 the car can go into limp mode (reduced power) to protect itself.
Will C0664 fail an emissions test?
C0664 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 C0664 to fix?
Difficulty: medium. A typical repair takes 0.5 to 3 hours of work. This is a job for a workshop.
Will C0664 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.