C0303

Code

Generic C — Chassis

Wheel Speed Sensor Circuit Fault

Brand: Generic

Type: C — Chassis

Views: UK: 9 EN: 61 RU: 14

AI status

Completed

ready

Completed 100%

Page language: EN

Causes

Damaged or failed wheel speed sensor (magnetic/active)
Open, shorted or chafed wiring in the sensor harness
Corroded, loose or contaminated sensor connector
Broken, missing or heavily corroded tone ring/reluctor wheel
Incorrect sensor air gap or misalignment
Wheel bearing damage allowing sensor contact or signal loss

Symptoms

ABS warning light illuminated
Traction/stability control warning and/or disabled functions
Intermittent or no speed signal for one wheel in live data
ABS pump/cycle events during braking or reduced ABS functionality
Possible speedometer or cruise control anomalies (on some vehicles)
Pulsating brakes or unusual brake feel if tone ring or bearing is damaged

What to check

Read stored codes and freeze frame with a scan tool; note which wheel is affected
Check live wheel speed sensor data and compare all four wheel readings at slow wheel rotation
Visual inspection of the suspect sensor, wiring harness and connector for damage, contamination or corrosion
Inspect the tone ring (reluctor) for missing teeth, heavy rust, or debris
Backprobe sensor connector to check for supply voltage (active sensor) and ground integrity
Measure sensor resistance with ohmmeter (passive sensors) and compare to spec or opposite wheel

Signal parameters

Passive (VR) sensor: resistance typically 200–2,000 Ω (varies by vehicle); AC output varies with speed (≈0.1–4 VAC)
Active (powered) sensor: usually supplied with 5 V or reference; output is digital/square wave 0–5 V (or 0.2–4 V) with frequency proportional to speed
Typical frequency range: 0–2000 Hz depending on wheel speed and tooth count
Normal idle rotation output: small amplitude; amplitude and frequency increase smoothly with wheel rotation; missing pulses or flat signal indicates fault

Diagnostic algorithm

Safety first: safely support vehicle on stands and chock wheels before jack work
Retrieve DTC(s) and live data: confirm which wheel circuit (front/rear, left/right) is flagged
Visual inspection: inspect sensor, connector, tone ring and nearby wiring for damage, rubbing, corrosion or contaminants
Check connectors: disconnect sensor and inspect pins; clean and reseat connector; check for corrosion or bent pins
Measure sensor resistance (passive) at the sensor connector; compare to spec or the opposite wheel
Backprobe with key on and spin wheel: for active sensors verify reference voltage (typically 5V), ground, and output waveform; for passive sensors measure AC voltage while spinning
Wiggle test the harness while monitoring output to find intermittent faults
Check continuity from sensor connector to ABS module and for short to chassis ground or battery positive
Inspect tone ring: jack up wheel and rotate to observe damaged/missing teeth, heavy rust or foreign debris; check wheel bearing play
Repair as indicated: clean connectors, correct air gap, repair/replace wiring, repair or replace tone ring, or replace sensor
Clear codes, perform road test and re-scan; verify live data and absence of recurrence

Likely causes

Corroded/loose connector at the sensor
Open or short in the harness between sensor and ABS module
Contaminated or damaged tone ring (rust, missing teeth)
Failed wheel speed sensor

Fault status

⚠️ Status

ABS control module detected an abnormal or missing wheel speed sensor signal on the wheel speed circuit. Fault stored and related stability/ABS functions may be disabled until resolved.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 0.5-2.5 hours