Code
C0040
DAEWOO
C — Chassis
Right front wheel speed sensor circuit malfunction
AI status
Completed
Completed
100%
Causes
- Faulty right front wheel speed sensor
- Broken, pinched, corroded or disconnected wiring/connector to the sensor
- Damaged or missing tone ring/reluctor on the hub/axle
- Poor ground or low reference/return voltage
- Intermittent harness damage (chafing at suspension/wheel articulation points)
- Contaminated sensor (metal debris/grease) or excessive air gap
Symptoms
- ABS warning lamp illuminated
- Traction/stability control warning lamp illuminated or disabled
- Possible degraded ABS operation or wheel lock on hard braking
- Erratic or zero speed reading for the right front wheel in scan tool data
- Unusual noises from wheel bearing area or rubbing if tone ring damaged
What to check
- Read DTCs and freeze frame data with a capable scan tool; note vehicle speed and other active codes
- Visually inspect right front wheel, hub, tone ring/reluctor, sensor mounting and connector for damage, contamination or missing parts
- Inspect wiring along suspension and steering knuckles for chafing, breaks, or pinched sections
- Check connector pins for corrosion, bent pins, water ingress or poor contact
- Compare live wheel speed sensor values (RPM or speed) for all four wheels at low speed and while spinning the right front wheel by hand (with ignition on, wheels off ground)
- Measure sensor resistance with multimeter (if passive) and compare to specification / to the opposite side sensor
Signal parameters
- Passive (magnetic pickup) sensors: resistance typically ~500–1500 ohms (manufacturer-specific); AC sine pulses; amplitude increases with wheel speed (tens of mV to several volts)
- Active (Hall-effect/powered) sensors: square wave TTL-like or 0–5 V (or 0–12 V on some systems) with duty cycle ~50%; requires reference/supply (often 5 V) and ground
- Pulse frequency proportional to wheel speed; at low speeds expect low frequency (a few Hz) rising with vehicle speed
- Typical air gap between sensor and tone ring: ~0.5–2.0 mm (check OEM spec)
Diagnostic algorithm
- Connect scan tool, verify C0040 and any related ABS or wheel speed codes; record freeze frame and live data for wheel speed sensors.
- Visual inspection: check right front wheel sensor, harness, connector, tone ring, and wheel bearing area for physical damage, corrosion, or missing teeth.
- With ignition ON (engine off), backprobe sensor connector: verify reference supply voltage (if active sensor), ground continuity, and signal line behavior while spinning the wheel by hand. Compare to opposite (left front) sensor.
- Measure sensor resistance (for passive types) and compare to spec or the opposite side. Open or short indicates sensor replacement.
- Wiggle test wiring/connector while observing live data for intermittent changes. Repair any chafed or broken wiring.
- If wiring and connector are OK but signal is noisy or absent, bench-test or replace the sensor. If new sensor fails, inspect/replace tone ring if damaged or misaligned.
- Use oscilloscope to verify waveform quality (clean pulses), amplitude and frequency under wheel rotation. Replace sensor/harness/reluctor as indicated by tests.
- If wiring, sensor and tone ring are confirmed good, test or replace ABS/TC module or control unit as last resort (module driver fault).
- Clear codes, perform road test and re-check live data to confirm proper operation before returning vehicle to service.
Likely causes
- Failed right front wheel speed sensor
- Open or shorted wiring between sensor and ABS module (connector corrosion/damage)
- Damaged or missing tone ring/reluctor on the wheel/hub
- Poor sensor-to-reluctor air gap or misalignment
- Corroded connector/poor ground
Fault status
Status
Right front wheel speed sensor circuit malfunction — signal missing, intermittent, out of expected range, or short/open detected. ABS and traction control functions may be disabled for the affected wheel.
Repair difficulty: Medium
Diagnostic time: 1.0-2.0 hours
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Repair manuals
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75
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