C0663 Left Rear Wheel Speed Sensor B Intermittent/Erratic

Here the second left rear speed signal drops out for moments or jumps, without a lasting circuit fault. No public service data describes the code, so diagnosis has to follow the sensor principle. NXP's application note on magnetoresistive speed sensors warns that outside magnetic fields add to the measuring field: motors, relays and even wires carrying large currents close by can shift the signal far enough to lose pulses, and very strong fields can permanently change the magnet built into the sensor. On many cars the encoder is a magnetised ring in the wheel bearing seal; NTN-SNR points out that a magnetic screwdriver can erase its poles, which leaves gaps in the pulse train. C0663 also appears in GM's PIP5094 list, but only as an old, unrelated GM number.

Likely causes

Symptoms

• Warning comes and goes, often on rough roads
• Brief, unexpected stability or ABS interventions

Repair estimate

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

Parts involved

Related codes

References: nxp.com, techtalk.ie, static.nhtsa.gov.