C1002

Code

Generic C — Chassis

ABS wheel speed sensor circuit fault

Brand: Generic

Type: C — Chassis

Views: UK: 19 EN: 38 RU: 21

AI status

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Page language: EN

Causes

Damaged or contaminated wheel speed sensor
Open, shorted or corroded wiring/connectors between sensor and ABS module
Missing, damaged or dirty tone ring (reluctor) or magnet
Sensor misalignment or incorrect air gap
Failed ABS sensor (passive or active)
Faulty ABS control module or poor module ground

Symptoms

ABS warning lamp (and possibly traction/stability lamp) illuminated
Loss of ABS functionality; ABS may be disabled
Intermittent or no wheel speed reading for one wheel on live data
Possible stability control or traction control faults
Inconsistent speedometer or speed readings in some systems
Pulsating brake feel only when ABS activates (if available)

What to check

Read ABS codes with a capable scan tool and note freeze frame/live data
Visually inspect sensor, tone ring, harness and connectors for damage or contamination
Wiggle harness and connector while monitoring live wheel speed data for intermittency
Measure sensor resistance (for passive sensors) and compare with specification
Check sensor supply/reference voltage and ground (for active sensors)
Inspect tone ring for missing teeth, cracks, heavy rust or debris

Signal parameters

Passive (variable reluctance) sensors: generate AC voltage; amplitude increases with wheel speed. DC resistance typically in a vehicle-specific range (commonly a few hundred to a few thousand ohms).
Active (hall/effect) sensors: require reference voltage (commonly ~5V) and provide digital/sine-square pulses from ~0–5V; frequency increases with wheel speed.
Expected behavior: smooth, consistent waveform on oscilloscope and sensible wheel speed values on scan tool corresponding to vehicle motion.
Fault signatures: no signal (open), constant voltage (short to Vb), zero/near-zero (short to ground), erratic/noisy or missing pulses (tone ring damage or contamination).

Diagnostic algorithm

Safety: Park on level ground, chock wheels, lift and support vehicle safely if wheel rotation is required.
Scan tool: Read and record ABS codes and live data for all wheel speed sensors. Note which wheel is reporting the fault.
Visual: Inspect sensor area, wiring harness, connector seals, and tone ring for damage, debris, rust or missing teeth.
Wiggle test: With ignition on and scanner showing live wheel speed, gently wiggle the harness and connector to check for intermittent faults.
Electrical checks: Disconnect sensor connector. For passive sensors measure resistance between sensor terminals and compare to spec. For active sensors check reference voltage and ground at connector with ignition on.
Signal test: Reconnect and spin the wheel (or road test safely) while watching live data or using an oscilloscope to verify proper waveform and amplitude.
Continuity and short check: With ignition off, check continuity from sensor connector to ABS module and check for shorts to ground or battery on the circuit.
Tone ring check: Inspect and measure air gap; repair or replace damaged/missing tone ring or clean debris if present.
Replace suspected faulty sensor or repair wiring/connectors. Secure and protect harness from rubbing or heat.
After repair: Clear codes, perform a test drive while monitoring wheel speed signals and confirm ABS and traction functions operate normally.
If problem persists after sensor/harness repair, test/scan the ABS control module and grounds; consult manufacturer procedures for module diagnosis.