Chassis, generic

C0651 Left Front Wheel Speed Sensor B Circuit/Open

Check engine lightUsually off
EmissionsNot relevant
Drive cycleNot required
Limp modePossible

C0651 reports an open circuit at the second speed sensor of the left front wheel. Sensor B exists only where a wheel carries two independent speed signals, mainly in redundant brake systems for automated driving. Continental describes two layouts: two separate sensors per wheel, each wired to its own brake control unit, or one housing with two sensing elements, each with its own two-wire cable that can run to a different controller. On such two-wire sensors the signal rides on the supply current, and Allegro notes that the module can spot opens and shorts simply from the current drawn. No carmaker publishes C0651. Sensor A (C0500) usually keeps ABS working, but the redundancy is lost.

Likely causes

Broken wire in the sensor B cable near the wheel
Plug of the second channel loose or corroded
Second sensing element inside the sensor failed open

Symptoms

  • Warning for brake or driver assistance system
  • Automated driving or redundant brake functions unavailable

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€60–500
Time0.5–2 h

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

Parts involved

lf wss bsensor wiring

Related codes

C0652C0653C0654C0655C0500C0658

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