Code
C0306
HUMMER
C — Chassis
ABS Wheel Speed Sensor Circuit Malfunction
AI status
Completed
Completed
100%
Causes
- Open or shorted wiring in the wheel speed sensor circuit
- Corroded, damaged or loose connector at the sensor or ABS module
- Failed wheel speed sensor (active Hall-effect or passive tone sensor)
- Damaged or missing tone ring/reluctor wheel (broken teeth, heavy corrosion, or debris)
- Intermittent contact due to harness rubbing or pinched wiring
- Faulty ABS control module or poor ground/5V reference (less common)
Symptoms
- ABS warning lamp illuminated (may be lit continuously)
- Traction control or stability control warning lights may also be on
- ABS may be disabled; vehicle may feel different under hard braking
- Possible speedometer/odometer or transmission shift anomalies if vehicle speed signal affected
- Intermittent faults that appear while steering or driving over bumps
What to check
- Read ABS/vehicle scan tool for freeze frame and live data; identify which wheel circuit flagged
- Visually inspect sensor, connector, tone ring/reluctor and wiring harness for damage, contamination or debris
- Backprobe sensor connector with key on and check for reference voltage (typically 5V) and ground on active sensors
- Measure sensor output signal while spinning wheel (oscilloscope preferred) and verify frequency/voltage
- Check resistance/continuity of passive sensors and look for short to battery or ground
- Wiggle wiring and connectors while observing live data/comm to reproduce intermittent faults
Signal parameters
- Active (Hall-effect) sensors: expect a 5V reference, ground, and a pulsed 0–5V square wave signal; frequency proportional to wheel speed
- Passive (variable reluctor) sensors: produce an AC sine waveform; amplitude increases with wheel speed (low-speed amplitude may be
- Resistance: passive sensor DC resistance varies by design—consult vehicle service data; an open or short is a clear fault
- Frequency: pulses per wheel revolution equals number of tone ring teeth; pulse rate increases linearly with wheel speed
- Typical trouble signs: no signal, constant DC, excessive noise, missing pulses or irregular amplitude
Diagnostic algorithm
- Connect a compatible scan tool and read ABS codes and live wheel speed data. Note which wheel circuit is flagged.
- Perform a visual inspection of the sensor, connector, tone ring, hub and wiring for damage, corrosion, contamination or loose mounting.
- With ignition on (engine off), backprobe connector: verify reference voltage (if applicable) and good ground. Replace or repair if reference or ground missing.
- Measure sensor output while rotating the wheel by hand or with the vehicle raised. Use an oscilloscope to verify a clean waveform (pulses for Hall sensors, AC sine for passive sensors).
- Check DC resistance of passive sensors and compare to specification. If open/short or out of range, replace sensor.
- Wiggle the harness and connector while watching live data to find intermittent opens/shorts. Repair broken wires, pins, or replace connector as needed.
- Inspect tone ring for damaged/missing teeth, heavy rust or metal debris. Clean or replace tone ring/hub if abnormalities present.
- If sensor and wiring check good, inspect ABS module connector for corrosion and test module input if procedures available. Avoid module replacement until wiring and sensor are verified.
- After repair, clear codes and perform a road test while monitoring wheel speed signals to confirm proper operation and that the code does not return.
- Safety note: support vehicle on jack stands before rotating wheels and follow manufacturer lift/jack procedures.
Likely causes
- Corroded or loose sensor connector at wheel hub
- Damaged harness where it flexes (suspension pivot or steering boot)
- Failed sensor from contamination or impact
- Worn/damaged tone ring (wheel hub or axle reluctor)
Fault status
Status
ABS control module detected a malfunction in a wheel speed sensor circuit — either missing, intermittent, out-of-range or shorted signal. ABS/traction control functions for the affected wheel may be disabled until fault is resolved.
Repair difficulty: Medium
Diagnostic time: 0.5-2.0 hours
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