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C0668 — Right Rear Wheel Speed Sensor B Circuit Low

Generic OBD-II · all makesChassis

This diagnostic trouble code indicates the ABS control module detects a voltage signal from the right rear wheel speed sensor that is below the expected operating range. This condition typically suggests an electrical fault such as a short to ground, a broken wire, or an internal sensor failure. The ABS system will usually disable anti-lock functions until the fault is resolved.

Symptoms

What causes it — most likely first

1. Failed wheel speed sensor

Internal electrical failure within the sensor unit causes a low voltage signal.

2. Damaged wiring harness

Wires near the wheel may be chafed, melted, or shorted to ground due to heat or movement.

3. Corroded electrical connector

Moisture or debris at the sensor plug creates high resistance or poor contact.

4. Damaged tone ring

Missing teeth or cracks on the reluctor ring prevent proper signal generation.

5. Poor system ground

A corroded ground strap for the ABS system can cause low voltage readings.

6. Internal ABS control module failure

Rare internal fault within the module itself; only considered after all external circuits are verified.

How it's diagnosed

  1. Perform visual inspection of the right rear sensor wiring and connector for damage
  2. Measure sensor resistance and compare to manufacturer specifications
  3. Check wiring continuity between the sensor connector and the ABS module
  4. Inspect the tone ring for cracks, missing teeth, or debris
  5. Clear the code and test drive while monitoring live wheel speed data
  6. Test ABS module power and ground circuits before considering module replacement

Code facts & related codes

SystemChassis
StandardizationSAE generic — identical on every make

Frequently asked

Is the ABS computer usually the cause of this code?

No, external sensors and wiring fail much more frequently than the control module.

Is it safe to drive with this code active?

The vehicle will brake normally, but anti-lock and traction features will not function during emergency maneuvers.

Can a bad bearing trigger this code?

Yes, excessive wheel bearing play can alter the sensor gap and cause erratic signals.

Should the control module be replaced immediately?

No, module replacement is rarely required unless all wiring and sensor tests pass.