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C0663 — Left Rear Wheel Speed Sensor B Intermittenterratic

Generic OBD-II · all makesChassis

Diagnostic trouble code C0663 indicates an intermittent or erratic signal from the left rear wheel speed sensor, often labeled as 'Sensor B' on vehicles with dual sensors per wheel. This code is triggered when the ABS control module detects an unstable or missing signal from that sensor, which can affect anti-lock braking, traction control, and stability systems.

Symptoms

What causes it — most likely first

1. Faulty left rear wheel speed sensor

The sensor itself may have internal damage, corrosion, or an intermittent electrical failure. This is the most common cause.

2. Damaged or corroded wiring/connector

The wiring harness or connector at the left rear wheel can suffer from chafing, corrosion, or loose pins, causing an intermittent signal.

3. Dirty or damaged tone ring (reluctor ring)

The tone ring attached to the wheel hub or axle may be cracked, missing teeth, or contaminated with debris, leading to erratic sensor readings.

4. Wheel bearing play affecting sensor gap

Excessive play in the wheel bearing can alter the air gap between the sensor and tone ring, causing intermittent signal loss.

5. ABS module internal fault

Less commonly, the ABS control module may have an internal issue that misinterprets a valid sensor signal as erratic. This is rare and should only be considered after thoroughly checking the sensor and wiring.

How it's diagnosed

  1. Visually inspect the left rear wheel speed sensor, wiring, and connector for damage, corrosion, or loose connections.
  2. Measure the sensor's resistance with a multimeter and compare to manufacturer specifications (typically 1–2 kΩ).
  3. Raise the vehicle and spin the left rear wheel while monitoring the sensor's AC voltage output; it should increase smoothly with wheel speed.
  4. Inspect the tone ring (reluctor ring) for cracks, missing teeth, or debris buildup.
  5. Check for excessive wheel bearing play that could alter the sensor-to-tone-ring gap.
  6. If all above checks pass, consider testing the ABS module by swapping with a known-good unit or performing a module-specific diagnostic scan.

Code facts & related codes

SystemChassis
StandardizationSAE generic — identical on every make
Related codesC0660 — Left Rear Wheel Speed Sensor B RangepeC0661 — Left Rear Wheel Speed Sensor B CircuitC0662 — Left Rear Wheel Speed Sensor B CircuitC0664 — Left Rear Wheel Speed Sensor B CorrelaC0665 — Left Rear Wheel Speed Sensor B IncorreC0666 — Right Rear Wheel Speed Sensor B Circui

Frequently asked

Can I drive my car with code C0663?

Yes, you can usually drive, but the ABS and traction control systems will likely be disabled. The standard braking system will still work, but you may lose stability control in slippery conditions. It's best to diagnose and repair the issue promptly.

Do I need to replace the ABS control module for this code?

Almost never. The ABS module is rarely the cause of a wheel speed sensor code. The vast majority of C0663 issues are due to a faulty sensor, damaged wiring, or a contaminated/damaged tone ring. Only consider the module after thoroughly testing the sensor and its circuit.

What is the difference between Sensor A and Sensor B for the same wheel?

Some vehicles use two wheel speed sensors per wheel for redundancy or to support advanced stability control systems. Sensor B is typically the secondary sensor. The diagnostic approach is the same: inspect the sensor, wiring, and tone ring for that specific sensor.

Will this code clear itself after fixing the issue?

If the repair is successful, the code may clear after several drive cycles with no fault detected. However, it is often necessary to manually clear the code with a scan tool to reset the ABS module and turn off the warning lights.