Code
C0235
Generic
C — Chassis
ABS Wheel Speed Sensor Circuit Malfunction
AI status
Completed
Completed
100%
Causes
- Damaged or failed wheel speed sensor (magnetic/VR or Hall type)
- Broken, pinched, chafed or corroded wiring harness or connector
- Poor pin/contact connection or corrosion at the sensor connector
- Damaged or missing tone/ring wheel (reluctor) or heavy contamination
- Wheel bearing/seal metal debris interfering with sensor
- Faulty ABS/traction control module or internal connector
Symptoms
- ABS warning light illuminated
- Traction control/stability light may be illuminated or systems disabled
- ABS/traction control functionality may be lost or operate intermittently
- Brake pedal feel may be normal but ABS intervention will not occur
- Speedometer or cruise control may behave erratically on some vehicles
- Possible intermittent fault depending on vehicle speed or road conditions
What to check
- Read and record freeze-frame and stored ABS codes with a scan tool; confirm C0235 is current/active
- Perform a visual inspection of the suspect wheel hub area, sensor, tone ring, and wiring for damage, debris, or corrosion
- Check connector for corrosion, bent pins, water intrusion, or poor seating
- Measure sensor resistance at the connector (compare to spec) and check for opens/shorts to ground/power
- Back-probe sensor while rotating wheel (or drive carefully) to observe signal with oscilloscope or multimeter
- Wiggle harness and joints to reproduce intermittent failures while monitoring signal
Signal parameters
- Variable reluctance (VR) sensor: AC sine waveform whose amplitude and frequency increase with wheel speed; small amplitude at low speed (tenths to a few volts AC) rising to several volts AC at higher speeds
- Hall-effect sensor: digital square/pulse waveform referenced to vehicle ground; typically a 0–5 V (or 0–12 V on some systems) pulse depending on supply; frequency proportional to wheel speed
- Typical static resistance for VR sensors often in the few hundred to a few thousand ohms (manufacturer specific) — an open or shorted reading indicates failure
- Expected waveform on oscilloscope: clean, consistent pulses or sine waves without dropouts, distortion, or excessive noise; missing pulses or erratic amplitude indicates problem
- Signal frequency should rise smoothly with wheel rotation; abrupt omissions or intermittent signals indicate wiring or sensor issues
Diagnostic algorithm
- Use a scan tool to confirm C0235 and note freeze-frame data. Clear codes and perform a short road test to see if code returns.
- Visually inspect the suspect wheel hub, sensor, tone ring, and wiring for damage, contamination, or loose connectors. Repair obvious issues.
- Disconnect the sensor connector and check pins for corrosion, bent pins, or water intrusion. Clean and reseal if needed.
- Measure sensor resistance (for VR sensors) and compare to specification. Check for short to ground or battery. Replace sensor if open or out of spec.
- Back-probe the sensor connector and spin the wheel (or use a scope while driving slowly) to observe the signal waveform. Look for missing pulses, low amplitude, noise, or intermittent signal.
- Wiggle the wiring and suspension components while monitoring the signal to find intermittent wiring faults.
- Inspect the tone ring for missing teeth, cracks, heavy rust, or contact with sensor. Correct the tone ring position or replace if damaged.
- Check power supply and ground on Hall-type sensors (usually 5 V reference) and verify ECU connector continuity back to the ABS module.
- If wiring and sensor check good, test continuity from sensor connector to ABS module pins to isolate harness faults.
- If available, swap with a known-good sensor (identical location/type) to confirm sensor vs. wiring/module. Replace faulty component and clear codes.
- After repair, perform road test and confirm proper sensor waveform and that the code does not return. Relearn or calibrate wheel sensors if required by manufacturer procedures.
Likely causes
- Failed wheel speed sensor (most common)
- Open or short in sensor wiring or poor connector contact
- Contaminated or damaged reluctor/tone ring
- Intermittent connection caused by wiring rubbing at suspension components
- Less likely: defective ABS control module
Fault status
Status
ABS control module reports a wheel speed sensor circuit malfunction. ABS and traction/stability systems may be disabled or degraded until the sensor circuit is repaired and the code cleared.
Repair difficulty: Medium
Diagnostic time: 0.5-2.0 hours
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Code
C0235
HUMMER
C — Chassis
Left Rear Wheel Speed Sensor Circuit Fault
AI status
Completed
Completed
100%
Causes
- Damaged or failed wheel speed sensor (magnetic/VR or Hall type)
- Broken, pinched, chafed or corroded wiring harness or connector
- Poor pin/contact connection or corrosion at the sensor connector
- Damaged or missing tone/ring wheel (reluctor) or heavy contamination
- Wheel bearing/seal metal debris interfering with sensor
- Faulty ABS/traction control module or internal connector
Symptoms
- ABS warning light illuminated
- Traction control/stability light may be illuminated or systems disabled
- ABS/traction control functionality may be lost or operate intermittently
- Brake pedal feel may be normal but ABS intervention will not occur
- Speedometer or cruise control may behave erratically on some vehicles
- Possible intermittent fault depending on vehicle speed or road conditions
What to check
- Read and record freeze-frame and stored ABS codes with a scan tool; confirm C0235 is current/active
- Perform a visual inspection of the suspect wheel hub area, sensor, tone ring, and wiring for damage, debris, or corrosion
- Check connector for corrosion, bent pins, water intrusion, or poor seating
- Measure sensor resistance at the connector (compare to spec) and check for opens/shorts to ground/power
- Back-probe sensor while rotating wheel (or drive carefully) to observe signal with oscilloscope or multimeter
- Wiggle harness and joints to reproduce intermittent failures while monitoring signal
Signal parameters
- Variable reluctance (VR) sensor: AC sine waveform whose amplitude and frequency increase with wheel speed; small amplitude at low speed (tenths to a few volts AC) rising to several volts AC at higher speeds
- Hall-effect sensor: digital square/pulse waveform referenced to vehicle ground; typically a 0–5 V (or 0–12 V on some systems) pulse depending on supply; frequency proportional to wheel speed
- Typical static resistance for VR sensors often in the few hundred to a few thousand ohms (manufacturer specific) — an open or shorted reading indicates failure
- Expected waveform on oscilloscope: clean, consistent pulses or sine waves without dropouts, distortion, or excessive noise; missing pulses or erratic amplitude indicates problem
- Signal frequency should rise smoothly with wheel rotation; abrupt omissions or intermittent signals indicate wiring or sensor issues
Diagnostic algorithm
- Use a scan tool to confirm C0235 and note freeze-frame data. Clear codes and perform a short road test to see if code returns.
- Visually inspect the suspect wheel hub, sensor, tone ring, and wiring for damage, contamination, or loose connectors. Repair obvious issues.
- Disconnect the sensor connector and check pins for corrosion, bent pins, or water intrusion. Clean and reseal if needed.
- Measure sensor resistance (for VR sensors) and compare to specification. Check for short to ground or battery. Replace sensor if open or out of spec.
- Back-probe the sensor connector and spin the wheel (or use a scope while driving slowly) to observe the signal waveform. Look for missing pulses, low amplitude, noise, or intermittent signal.
- Wiggle the wiring and suspension components while monitoring the signal to find intermittent wiring faults.
- Inspect the tone ring for missing teeth, cracks, heavy rust, or contact with sensor. Correct the tone ring position or replace if damaged.
- Check power supply and ground on Hall-type sensors (usually 5 V reference) and verify ECU connector continuity back to the ABS module.
- If wiring and sensor check good, test continuity from sensor connector to ABS module pins to isolate harness faults.
- If available, swap with a known-good sensor (identical location/type) to confirm sensor vs. wiring/module. Replace faulty component and clear codes.
- After repair, perform road test and confirm proper sensor waveform and that the code does not return. Relearn or calibrate wheel sensors if required by manufacturer procedures.
Likely causes
- Failed wheel speed sensor (most common)
- Open or short in sensor wiring or poor connector contact
- Contaminated or damaged reluctor/tone ring
- Intermittent connection caused by wiring rubbing at suspension components
- Less likely: defective ABS control module
Fault status
Status
ABS control module reports a wheel speed sensor circuit malfunction. ABS and traction/stability systems may be disabled or degraded until the sensor circuit is repaired and the code cleared.
Repair difficulty: Medium
Diagnostic time: 0.5-2.0 hours
Similar codes
Repair manuals
Manual library for HUMMER
138
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