Chassis, generic

C0664 Left Rear Wheel Speed Sensor B Correlation

Check engine lightUsually off
EmissionsNot relevant
Drive cycleRequired
Limp modePossible

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.

Likely causes

Damaged or wrong encoder ring giving a false pulse count
Tyre of different size or heavily worn on the left rear
Sensor B losing pulses at high speed

Symptoms

  • Warning set after a longer drive, not at start
  • Automated or redundant brake functions refused

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€60–900
Time0.5–3 h

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

Parts involved

lr wss blr wsstone ring

Related codes

C0660C0663C0665C0511C066B

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