C1A45

Code

Generic C — Chassis

Rear Left Wheel Speed Sensor - Intermittent Signal

Brand: Generic

Type: C — Chassis

Views: UK: 16 EN: 23 RU: 13

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ABS warning lamp and/or traction control (TC/ESC) lamp illuminated intermittently
Inconsistent or jumping vehicle speed or speedometer glitches (in some vehicles)
ABS activation at low/no braking speeds or unexpected traction control events
Diagnostic trouble code returns after driving or on road test, may clear and return
Possible unusual noise from wheel area if tone ring or bearing is damaged

Scan tool: read freeze frame and live wheel speed values while rotating each wheel (on-lift or road test).
Visually inspect sensor, connector, and tone ring for damage, debris, or missing teeth.
Wiggle harness and connector while monitoring live data or using an oscilloscope to reproduce the intermittent.
Check sensor wiring continuity, resistance and insulation (open/short to ground or power).
Measure sensor resistance (for passive VR sensors) and compare to spec; check supply/reference and output for active sensors.
Use an oscilloscope to verify signal waveform (VR = AC sine; Hall = square/pulse) while spinning the wheel.

Passive (variable reluctance) sensor: AC sine waveform; amplitude increases with speed (tens of mV at low speed up to volts at higher speed); typical DC resistance often in the hundreds to a few thousand ohms (vehicle-specific).
Active (Hall/LS) sensor: square/pulse waveform referenced to sensor supply; 0–5 V (or 0–12 V on some systems) pulses; requires a stable supply/reference and ground from ABS module.
Pulse frequency proportional to wheel speed: freq = wheel RPM × (tone ring teeth) / 60. Expect steady, evenly spaced pulses for a healthy tone ring.
Intermittent fault often shows missing pulses, dropped cycles, noisy or distorted waveform, or intermittent loss of amplitude.

Retrieve code and freeze-frame with a scan tool. Confirm only rear left sensor intermittent code and note conditions (speed, temp).
Inspect the rear left sensor, connector, and tone ring for visible damage, corrosion, debris or missing teeth. Correct obvious issues.
With ignition on, back-probe the sensor connector and check for proper reference supply and ground (active sensors).
Measure sensor resistance (passive) and compare to spec. Check for short to ground or short to battery on wiring.
Monitor live wheel speed data on scan tool while lifting vehicle and spinning wheel by hand; look for dropouts or inconsistent readings.
Wiggle the wiring harness, suspension components and connector while observing live data or oscilloscope to reproduce intermittent behavior.
Use an oscilloscope at the sensor connector to inspect waveform while wheel is turned at different speeds; look for missing pulses, noise, or amplitude changes.
If waveform or wiring is bad, repair or replace damaged wiring, clean/replace connector, or replace the sensor as needed.
If wiring and sensor test good, inspect and measure tone ring concentricity and tooth condition; repair or replace if damaged.
After repairs, clear codes, perform road test to verify the fault does not return and that live wheel speed signals remain stable under load and cornering.
If intermittent persists and wiring/sensor are confirmed good, consider ABS module input circuit testing or professional module diagnostics.

Connector corrosion or water intrusion causing intermittent contact
Pinched/frayed wiring at suspension pivot or behind wheel well
Physical damage or missing teeth on tone ring producing irregular pulses
Sensor mounting loose or incorrect air gap causing intermittent signal
Intermittent short to battery or ground when harness moves (road/load dependent)