C0300: Rear Speed Sensor Circuit Malfunction

What Does C0300 Mean?

Code C0300 indicates a general rear speed sensor circuit fault detected by the ABS module. On some vehicles, particularly those with a rear-wheel ABS system, a single sensor on the rear axle or differential provides speed data. This code means that sensor circuit has an electrical problem preventing accurate speed measurement.

Common Causes

• Failed rear axle speed sensor
• Damaged tone ring in the rear differential
• Corroded sensor connector near the rear axle
• Wiring damage from road debris or dragging
• Rear differential fluid contaminating the sensor

Symptoms

• ABS warning light on
• Rear ABS disabled
• Brake warning light may illuminate
• Traction control disabled
• Speedometer may be inaccurate on some vehicles

Diagnostic Steps

1. 1Read ABS codes with scan tool
2. 2Locate and inspect the rear speed sensor on the axle housing or differential
3. 3Check sensor wiring from the axle back to the ABS module
4. 4Clean metallic debris from the sensor tip
5. 5Measure sensor resistance and compare to specs
6. 6Inspect the tone ring inside the differential if accessible

Estimated Repair Cost

Frequently Asked Questions