C1100 — Left Front Axle VSS Circuit Fault

Causes

• Open or short in left front wheel speed sensor wiring
• Corroded/loose connector or pin at the sensor or ABS module
• Failed left front wheel speed sensor (passive or active type)
• Damaged tone ring (reluctor) or missing teeth
• Contaminated sensor air gap (metal shavings, debris, rust)
• Faulty ABS/ESP control module or poor ground/power supply

Symptoms

• ABS, ESP or traction control warning lamp illuminated
• Possible loss of ABS or traction control functionality
• Inconsistent or no speed reading from left front wheel in scanner/live data
• Occasional pulsing of brake pedal or unexpected ABS activation
• Noise or roughness from wheel area if tone ring or bearing damaged

What to check

• Read and record freeze-frame and related codes with a capable scan tool
• Compare left front wheel speed live data to other wheels at low speed
• Visual inspection of sensor, wiring, and connector for damage, corrosion, or contamination
• Check for damaged tone ring, missing teeth, heavy rust or metal debris
• Back-probe sensor connector to verify reference/power/ground (if active sensor) or continuity (if passive)
• Measure sensor resistance with meter (for passive sensors) and check for shorts to ground/12V

Signal parameters

• Passive (variable reluctance) sensors: DC resistance typically ~500–2,000 ohms (vehicle-specific); AC voltage increases with wheel speed — low RPM = small AC mV, higher RPM = larger mV
• Active (Hall/VR with electronics) sensors: require reference voltage (often 5V or switched 12V) and produce a digital/square or pulsed signal 0–5V (or open-collector) synchronized to wheel rotation
• Waveform: clean sinusoidal (passive) or square/pulsed (active) with frequency proportional to wheel speed; missing pulses, noise, or DC offset indicate fault
• Typical test condition: signal frequency and amplitude should increase smoothly as wheel is rotated; no signal or intermittent pulses indicates circuit/sensor problem

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