Code
C0660
Generic
C — Chassis
Left Rear Wheel Speed Sensor B Range/Performance
AI status
Completed
Completed
100%
Causes
- Wheel speed sensor circuit fault (open/short/intermittent)
- Failed wheel speed sensor element
- Physical damage or contamination of sensor or tone ring
- Excessive sensor-to-tone-ring air gap or misalignment
- Corroded or loose connector/ground/power supply
- Faulty ABS/traction control module or internal processing error
Symptoms
- ABS warning lamp and/or traction control warning lamp illuminated
- Reduced or disabled ABS/traction control functionality
- ABS activates unexpectedly or fails to activate when braking
- Inconsistent wheel speed readings on a scan tool (erratic, zero, or stuck value)
- Possible speedometer, cruise control, or stability control anomalies
- Noise from wheel area or evidence of physical damage near sensor
What to check
- Read ABS codes and live wheel speed data with a scan tool; note behavior at rest and during wheel spin
- Visually inspect sensor, tone ring/reluctor, and wiring for damage, contamination, missing teeth, or excessive play
- Check sensor connector for corrosion, bent pins, or moisture; unplug and inspect terminals
- Measure sensor resistance and compare to manufacturer specification
- For passive sensors: measure AC voltage while spinning the wheel; for active sensors: verify reference power, ground, and digital output
- Backprobe wiring to check for continuity to ABS module and for shorts to power/ground
Signal parameters
- Passive (magnetic pickup): AC voltage waveform whose frequency and amplitude increase with wheel speed; amplitude typically increases with RPM (specific mV–V depends on sensor design)
- Active (Hall-effect/MR): digital square-wave output referenced to ground, typically 0–5V (or vehicle reference) with frequency proportional to wheel speed; duty cycle often near 50%
- Sensor resistance should match manufacturer specification (varies by model; can be hundreds to low thousands of ohms for passive sensors)
- Reference/pull-up voltage for active sensors typically supplied by ABS module (commonly 5V reference or module-specific voltage)
- Waveform should be stable and continuous without dropouts, noise spikes, or missing pulses compared to other wheel signals
Diagnostic algorithm
- Verify and record ABS fault codes and freeze frame; note when the fault is active and any other related codes.
- Using a scan tool, observe live wheel speed values for all four wheels at low speed or with the wheel lifted. Confirm left rear differs or is erratic.
- Visually inspect left rear sensor, tone ring, and harness for damage, contamination, or missing teeth. Repair or clean as needed.
- Inspect and clean the sensor connector; check for corrosion and secure pin fit. Reconnect and recheck codes/live data.
- Measure sensor resistance with meter (engine off) and compare to spec. For passive sensors, spin wheel and measure AC voltage. For active sensors, check reference voltage and signal output while spinning.
- Perform a wiggle test on harness and connector while monitoring live data to find intermittent faults.
- If wiring or connector faults are found, repair with proper terminals, seals, and insulation; then retest.
- If sensor output is out of spec or missing, replace the sensor and confirm tone ring condition; replace tone ring if damaged.
- If sensor and wiring test good, inspect ABS module power/ground and communication lines; consider module diagnostics or replacement if internal circuit fault is suspected.
- Clear codes and perform a road test to verify the repair. Re-scan to ensure code does not return.
Likely causes
- Damaged sensor wiring harness (chafed, pinched, or broken)
- Corroded connector pins at sensor or ABS module
- Contaminated or cracked sensor or tone ring (metal shavings, rust)
- Missing or broken teeth on tone ring or reluctor
- Sensor mounted with excessive air gap after service or crash
- Failed Hall-effect/Magneto-resistive pickup or passive coil
Fault status
Status
ABS module detected left rear wheel speed sensor (B) signal out of expected range or inconsistent with other wheel speed signals. This may be due to sensor, wiring, tone ring, or module fault.
Repair difficulty: Medium
Diagnostic time: 0.5-2.5 hours
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Code
C0660
HUMMER
C — Chassis
Level Control Exhaust Valve Circuit Malfunction
AI status
Completed
Completed
100%
Causes
- Wheel speed sensor circuit fault (open/short/intermittent)
- Failed wheel speed sensor element
- Physical damage or contamination of sensor or tone ring
- Excessive sensor-to-tone-ring air gap or misalignment
- Corroded or loose connector/ground/power supply
- Faulty ABS/traction control module or internal processing error
Symptoms
- ABS warning lamp and/or traction control warning lamp illuminated
- Reduced or disabled ABS/traction control functionality
- ABS activates unexpectedly or fails to activate when braking
- Inconsistent wheel speed readings on a scan tool (erratic, zero, or stuck value)
- Possible speedometer, cruise control, or stability control anomalies
- Noise from wheel area or evidence of physical damage near sensor
What to check
- Read ABS codes and live wheel speed data with a scan tool; note behavior at rest and during wheel spin
- Visually inspect sensor, tone ring/reluctor, and wiring for damage, contamination, missing teeth, or excessive play
- Check sensor connector for corrosion, bent pins, or moisture; unplug and inspect terminals
- Measure sensor resistance and compare to manufacturer specification
- For passive sensors: measure AC voltage while spinning the wheel; for active sensors: verify reference power, ground, and digital output
- Backprobe wiring to check for continuity to ABS module and for shorts to power/ground
Signal parameters
- Passive (magnetic pickup): AC voltage waveform whose frequency and amplitude increase with wheel speed; amplitude typically increases with RPM (specific mV–V depends on sensor design)
- Active (Hall-effect/MR): digital square-wave output referenced to ground, typically 0–5V (or vehicle reference) with frequency proportional to wheel speed; duty cycle often near 50%
- Sensor resistance should match manufacturer specification (varies by model; can be hundreds to low thousands of ohms for passive sensors)
- Reference/pull-up voltage for active sensors typically supplied by ABS module (commonly 5V reference or module-specific voltage)
- Waveform should be stable and continuous without dropouts, noise spikes, or missing pulses compared to other wheel signals
Diagnostic algorithm
- Verify and record ABS fault codes and freeze frame; note when the fault is active and any other related codes.
- Using a scan tool, observe live wheel speed values for all four wheels at low speed or with the wheel lifted. Confirm left rear differs or is erratic.
- Visually inspect left rear sensor, tone ring, and harness for damage, contamination, or missing teeth. Repair or clean as needed.
- Inspect and clean the sensor connector; check for corrosion and secure pin fit. Reconnect and recheck codes/live data.
- Measure sensor resistance with meter (engine off) and compare to spec. For passive sensors, spin wheel and measure AC voltage. For active sensors, check reference voltage and signal output while spinning.
- Perform a wiggle test on harness and connector while monitoring live data to find intermittent faults.
- If wiring or connector faults are found, repair with proper terminals, seals, and insulation; then retest.
- If sensor output is out of spec or missing, replace the sensor and confirm tone ring condition; replace tone ring if damaged.
- If sensor and wiring test good, inspect ABS module power/ground and communication lines; consider module diagnostics or replacement if internal circuit fault is suspected.
- Clear codes and perform a road test to verify the repair. Re-scan to ensure code does not return.
Likely causes
- Damaged sensor wiring harness (chafed, pinched, or broken)
- Corroded connector pins at sensor or ABS module
- Contaminated or cracked sensor or tone ring (metal shavings, rust)
- Missing or broken teeth on tone ring or reluctor
- Sensor mounted with excessive air gap after service or crash
- Failed Hall-effect/Magneto-resistive pickup or passive coil
Fault status
Status
ABS module detected left rear wheel speed sensor (B) signal out of expected range or inconsistent with other wheel speed signals. This may be due to sensor, wiring, tone ring, or module fault.
Repair difficulty: Medium
Diagnostic time: 0.5-2.5 hours
Similar codes
Repair manuals
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