C1A25

Code

Generic C — Chassis

Left Rear Wheel Speed Sensor Circuit Intermittent

Brand: Generic

Type: C — Chassis

Views: UK: 4 EN: 1 RU: 1

AI status

Completed

ready

Completed 100%

Page language: EN

Causes

Corroded or loose sensor connector
Damaged or broken wiring/harness (intermittent open or short)
Contaminated, damaged, or misaligned tone ring/reluctor
Faulty wheel speed sensor (intermittent internal failure)
Excessive wheel bearing play or mechanical damage affecting sensor gap
Poor ground or power supply to ABS/ESC module or sensor (if active sensor)

Symptoms

ABS and/or traction control warning lamp illuminates intermittently
Intermittent ABS activation or unexpected ABS/ESC behavior
ABS/ESC faults stored in scan tool with left rear sensor code
Inconsistent or jumping wheel speed reading for left rear in live data
Possible traction control intervention while driving at low speed

What to check

Read all stored and pending ABS/ESC codes and freeze frame data with a scan tool
Inspect left rear wheel speed sensor, harness, and connector for damage, corrosion, or contamination
Check tone ring (reluctor) for missing or damaged teeth, heavy rust, or debris
Backprobe connector and observe live sensor data while spinning wheel or test-driving (or raising vehicle)
Perform wiggle test of harness and connector while monitoring live data for dropouts
Measure sensor resistance and continuity of wiring to module (compare to service spec if available)

Signal parameters

Passive (variable reluctance) sensor: AC sine-like waveform; amplitude increases with wheel speed (typical 0.1–several volts AC depending on design)
Active (Hall/magnetoresistive) sensor: digital square/pulse waveform, typically 0–5V (or 0–12V on some systems); frequency proportional to wheel speed
Frequency: proportional to wheel speed — low frequencies at low speed up to kHz-range at high speed depending on tone ring tooth count
Expected behavior: steady, continuous pulses without dropouts or large amplitude dips as wheel turns
Intermittent fault: occasional missing pulses, irregular amplitude, or noisy/distorted waveform

Diagnostic algorithm

Verify the code is current or historic and note conditions (speed, temperature, steering, road surface) from freeze frame.
Visually inspect sensor, harness, and connector at left rear for obvious damage, pin corrosion, or trapped debris; repair any issues found.
Check the tone ring for missing or damaged teeth, heavy rust buildup, or an incorrect gap; correct as needed.
With a scan tool, view live left rear wheel speed data and compare to other wheels while spinning wheel by hand or driving slowly on a lift; look for dropouts or irregular readings.
Wiggle the wiring harness and connector while monitoring live data; note if the fault is reproduced — this locates an intermittent open/short.
Backprobe the sensor connector: for passive sensors measure AC output while spinning wheel; for active sensors check supply voltage, reference, and pulse output. Use an oscilloscope for intermittent waveform issues.
Measure continuity and resistance of the sensor and wiring to the ABS module; check for intermittent opens using a continuity tester while moving suspension.
Repair the identified fault (repair wiring, clean/replace connector, replace sensor or tone ring, secure ground/power). Avoid replacing the module unless all wiring/sensor checks are confirmed good.
Clear codes, perform a road test to verify the issue is resolved and that no return of the intermittent code occurs.

Likely causes

Worn or chafed wiring at suspension pivot points causing intermittent open
Corrosion at connector pins allowing intermittent contact
Sensor partially dislodged or gap varies with wheel movement
Damaged tone ring teeth or heavy rust/debris causing signal dropout
Intermittent short to chassis or short to other sensor circuit during wheel travel

Fault status

⚠️ Status

Intermittent fault detected in the left rear wheel speed sensor circuit — the ABS/ESC module is intermittently losing or receiving an invalid signal from the left rear wheel speed sensor.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 0.5-1.5 hours