◆OBD Codes

C0021

Left Rear Wheel Speed Sensor Circuit Range/Performance

Moderatesensor

Overview

The C0021 diagnostic trouble code means the chassis control module has identified a left rear wheel speed sensor circuit range/performance problem. This code indicates that a chassis sensor or its circuit is not providing expected readings to the ABS/stability control system. Accurate sensor data is essential for the proper operation of anti-lock brakes, traction control, and electronic stability control, and a fault in this circuit can cause these safety systems to be disabled.

Symptoms

  • ABS warning light illuminated on dashboard
  • Ride height abnormal or uneven
  • Traction control warning light on
  • Loss of anti-lock braking function

Common Causes

  • Excessive air gap between sensor and tone ring
  • Failed yaw rate or lateral accelerometer sensor
  • Contaminated or worn brake fluid level sensor
  • Damaged wheel bearing causing sensor misalignment

Diagnosis Steps

  1. 1Connect an OBD-II scanner and read all stored chassis trouble codes and freeze frame data
  2. 2Monitor wheel speed sensor signals using scan tool live data while driving
  3. 3Inspect the affected sensor and its wiring connector for damage or corrosion
  4. 4Check the sensor air gap and tone ring for damage, debris, or excessive wear
  5. 5Test the sensor resistance and voltage output with a multimeter; compare to specifications

Estimated Repair Cost

$100 — $500

Cost varies by vehicle, location, and repair shop. Includes parts and labor.

Commonly Affected Vehicles

Chevrolet EquinoxFord EscapeNissan AltimaMazda CX-5

Related Codes

C0040C0020C0146

More Sensor Codes

P0070Ambient Air Temperature Sensor Circuit
Low
P0071Ambient Air Temperature Sensor Range/Performance
Low
P0072Ambient Air Temperature Sensor Circuit Low
Low
P0073Ambient Air Temperature Sensor Circuit High
Low
P0074Ambient Air Temperature Sensor Circuit Intermittent
Low
P0095Intake Air Temperature Sensor 2 Circuit
Low

Frequently Asked Questions

The most common causes are a faulty sensor, damaged tone ring, excessive air gap, metallic debris on the sensor tip, corroded wiring, or a worn wheel bearing that allows the sensor to lose alignment with the tone ring.