Code
C0046
HUMMER
C — Chassis
Left Rear Wheel Speed Sensor Circuit Range/Performance (EBCM)
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UK: 22
EN: 29
RU: 25
AI status
Completed
Completed
100%
Causes
- Failed left rear wheel speed sensor (Hall or VR type)
- Damaged, shorted, open, or corroded wiring or connector at the left rear sensor
- Missing, damaged, dirty, or bent tone ring / reluctor or sensor air gap out of specification
- Poor ground or supply voltage to the sensor
- Wheel bearing damage or heavy contamination affecting sensor signal
- Intermittent connector contact from water/corrosion or physical damage
Symptoms
- ABS warning lamp (and possibly traction/stability warning) illuminated
- Loss of ABS or traction control functionality
- Vehicle may have reduced stability control or diagnostic limp safety strategies
- Possible incorrect or zero left rear wheel speed reading in scan tool data
- Brake pedal feel generally unchanged (unless other faults present)
- Possible wheel speed hysteresis or ABS activation at low speeds
What to check
- Connect a diagnostic scan tool and read live wheel speed values; compare left rear to other wheels at low speed.
- Inspect left rear wheel sensor, tone ring/reluctor and air gap for damage, debris, missing teeth or rust.
- Visually inspect wiring harness and connector for corrosion, bent pins, chafe locations, or water intrusion.
- Wiggle harness/connector while watching live data to find intermittent faults.
- Measure sensor resistance (for passive sensors) and compare to spec, and check supply/reference voltage for active sensors.
- Back-probe the sensor signal while spinning the wheel and observe waveform/voltage with an oscilloscope or scan tool if available.
Signal parameters
- Passive (magnetic/inductive) sensors: DC resistance typical ~800–2000 ohms (varies by sensor). AC output increases with speed — often 0.1–2.0 Vrms at low speed up to several volts at higher speeds. Frequency increases with wheel speed.
- Active (Hall/electronic) sensors: typically use a 5V (or sometimes 12V) reference; output is a square wave/pulse. Expected output swings ~0–5 V (or 0–12 V on some systems). Frequency correlates with wheel speed.
- At low crawl speed you should still see pulses; a completely flat/noisy/erratic signal indicates a fault.
- Compare observed amplitude and frequency against the other three wheel sensors on the same vehicle for consistency.
Diagnostic algorithm
- Retrieve freeze-frame and full code list; note any related ABS/traction codes. Record live wheel speed data at ignition ON and while moving slowly.
- Perform a visual inspection of the left rear sensor, tone ring, hub/bearing, and wiring harness. Clean any debris and correct obvious damage.
- With ignition OFF, disconnect the left rear sensor connector. Inspect pins and sockets for corrosion, bent pins, or moisture. Repair or replace connector as needed.
- Measure sensor resistance (if passive) and compare to specification. For active sensors, check reference supply voltage to the sensor with ignition ON. If out of spec, trace power/ground.
- Back-probe the sensor output and spin the wheel by hand (or safely lift vehicle and rotate wheel) while observing output on an oscilloscope or scan tool. Look for regular pulses and amplitude similar to other wheels.
- Wiggle the wiring harness from wheel to chassis/EBCM while watching live data to find intermittent faults. Check continuity from sensor connector to EBCM connector for opens/shorts to ground and other circuits.
- Inspect tone ring for missing teeth, heavy rust, or damage; measure sensor-to-tone ring air gap and correct per service spec.
- If wiring, connector, and tone ring check good but signal is still out of range, replace the left rear wheel speed sensor and retest.
- If a new sensor still shows the same issue and wiring to EBCM verifies good, consider EBCM or internal driver fault and follow manufacturer procedures for module testing/replacement.
- After repairs, clear codes and perform a road test while monitoring live data to confirm proper wheel speed signals and code does not return.
Likely causes
- Contaminated or damaged sensor or tone ring
- Open/short or corroded connector/wiring at left rear wheel
- Sensor air gap incorrect or sensor mechanically misaligned
- Failed sensor element
- Intermittent connector or poor ground
Fault status
Status
EBCM detected left rear wheel speed sensor circuit out of range or poor performance. The left rear wheel speed signal is missing, intermittent, or inconsistent with other wheel speeds.
Repair difficulty: Medium
Diagnostic time: 0.5-2.0 hours
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