Code
C0300
Generic
C — Chassis
Wheel Speed Sensor Circuit Malfunction (ABS)
Views:
UK: 10
EN: 64
RU: 18
AI status
Completed
Completed
100%
Causes
- Faulty wheel speed sensor (open, shorted, or electronic failure).
- Damaged, corroded, or disconnected sensor connector.
- Broken, missing or heavily corroded tone/reluctor ring (ABS ring).
- Wiring harness short to power/ground or open circuit to ABS module.
- Poor ground or supply voltage to an active sensor.
- Contamination (metal shavings, heavy rust) preventing correct sensor flux.
Symptoms
- ABS warning lamp illuminated; possible traction/stability warning lights.
- Intermittent or permanent loss of ABS/traction control functionality.
- ABS may not engage during a panic stop; braking may revert to non-ABS behavior.
- Erratic or zero wheel speed reading for one wheel in scan tool live data.
- Possible drivability complaints if vehicle stability/traction systems intervene unexpectedly.
What to check
- Scan for codes and any associated freeze-frame or related codes (other C-codes, U-codes, P0500).
- Inspect sensor and connector for corrosion, damage, contamination, or looseness.
- Visually inspect tone/reluctor ring for missing or damaged teeth and heavy corrosion.
- Check wiring for continuity and shorts between sensor signal, supply, and ground back to the ABS module.
- Monitor live wheel speed sensor data with a scan tool while rotating each wheel.
- Wiggle harness and connectors while watching live data to reproduce intermittent faults.
Signal parameters
- Passive (VR) sensor: AC sine/triangular waveform; amplitude increases with wheel speed. At low speeds expect small AC volts (typical low-speed output ~0.1–1.5 VAC, varies by design).
- Active (Hall or LSM) sensor: digital square wave or pulsed signal, typically 0–5V or 0–12V depending on vehicle; frequency proportional to wheel speed.
- Frequency/duty: pulse frequency rises in direct proportion to wheel speed; all wheel sensors should show consistent proportional values during a slow rotation.
- Resistance: single-wire VR sensors often have an ohms value (varies by OEM); verify sensor resistance against manufacturer specification.
- Continuity: signal wire should show continuity to the ABS module pin; check for short to chassis ground or battery.
Diagnostic algorithm
- Read and record all ABS and related codes. Note which wheel is referenced, if any, and any freeze-frame data.
- Perform a visual inspection of the indicated wheel sensor, connector, wiring, and tone ring for obvious damage, contamination or missing teeth.
- With ignition on, backprobe connector: for active sensors verify reference voltage (Vref) and ground; for passive sensors measure resistance across the sensor and compare to spec.
- Rotate the wheel by hand while monitoring live data on a scan tool: confirm the affected wheel reports a speed signal and compare to other wheels.
- If available, use an oscilloscope to view the sensor waveform while spinning the wheel — look for clean amplitude/frequency and no dropouts or noise.
- Perform a wiggle test of harness and connectors while watching live data to identify intermittent opens/shorts.
- Check continuity from sensor connector back to the ABS module pins and verify there are no shorts to battery or ground.
- If sensor and wiring check good but fault persists, swap sensor with the same-position sensor (if feasible) or substitute a known-good sensor to isolate sensor vs. module/wiring.
- Repair or replace damaged components (sensor, tone ring, wiring, connector). After repair clear codes, perform test drive and re-check for reoccurrence.
- If wiring and sensors are good and problem persists, test/inspect ABS module power/ground and communication lines or consult manufacturer-specific diagnostics for module faults.
Likely causes
- Corroded or wiggling connector at the wheel hub leading to intermittent signal.
- Sensor damaged by road debris or during wheel service.
- Tone ring tooth damage or missing teeth causing erratic waveform.
- Wire chafed where it passes through suspension or near the wheel hub.
- Failed active sensor electronics (no Vref or no square-wave output).
Fault status
Status
C0300 — Wheel Speed Sensor Circuit Malfunction (ABS). Stored when the ABS control module detects a missing, implausible, intermittent, or out-of-range wheel speed sensor signal from one wheel. Possible causes include sensor failure, wiring/connector issues, damaged tone ring, poor sensor supply/ground, or ABS module fault.
Repair difficulty: Medium
Diagnostic time: 1–3 hours
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Code
C0300
HUMMER
C — Chassis
Right Front Wheel Speed Sensor Circuit Malfunction
Views:
UK: 20
EN: 108
RU: 28
AI status
Completed
Completed
100%
Causes
- Faulty wheel speed sensor (open, shorted, or electronic failure).
- Damaged, corroded, or disconnected sensor connector.
- Broken, missing or heavily corroded tone/reluctor ring (ABS ring).
- Wiring harness short to power/ground or open circuit to ABS module.
- Poor ground or supply voltage to an active sensor.
- Contamination (metal shavings, heavy rust) preventing correct sensor flux.
Symptoms
- ABS warning lamp illuminated; possible traction/stability warning lights.
- Intermittent or permanent loss of ABS/traction control functionality.
- ABS may not engage during a panic stop; braking may revert to non-ABS behavior.
- Erratic or zero wheel speed reading for one wheel in scan tool live data.
- Possible drivability complaints if vehicle stability/traction systems intervene unexpectedly.
What to check
- Scan for codes and any associated freeze-frame or related codes (other C-codes, U-codes, P0500).
- Inspect sensor and connector for corrosion, damage, contamination, or looseness.
- Visually inspect tone/reluctor ring for missing or damaged teeth and heavy corrosion.
- Check wiring for continuity and shorts between sensor signal, supply, and ground back to the ABS module.
- Monitor live wheel speed sensor data with a scan tool while rotating each wheel.
- Wiggle harness and connectors while watching live data to reproduce intermittent faults.
Signal parameters
- Passive (VR) sensor: AC sine/triangular waveform; amplitude increases with wheel speed. At low speeds expect small AC volts (typical low-speed output ~0.1–1.5 VAC, varies by design).
- Active (Hall or LSM) sensor: digital square wave or pulsed signal, typically 0–5V or 0–12V depending on vehicle; frequency proportional to wheel speed.
- Frequency/duty: pulse frequency rises in direct proportion to wheel speed; all wheel sensors should show consistent proportional values during a slow rotation.
- Resistance: single-wire VR sensors often have an ohms value (varies by OEM); verify sensor resistance against manufacturer specification.
- Continuity: signal wire should show continuity to the ABS module pin; check for short to chassis ground or battery.
Diagnostic algorithm
- Read and record all ABS and related codes. Note which wheel is referenced, if any, and any freeze-frame data.
- Perform a visual inspection of the indicated wheel sensor, connector, wiring, and tone ring for obvious damage, contamination or missing teeth.
- With ignition on, backprobe connector: for active sensors verify reference voltage (Vref) and ground; for passive sensors measure resistance across the sensor and compare to spec.
- Rotate the wheel by hand while monitoring live data on a scan tool: confirm the affected wheel reports a speed signal and compare to other wheels.
- If available, use an oscilloscope to view the sensor waveform while spinning the wheel — look for clean amplitude/frequency and no dropouts or noise.
- Perform a wiggle test of harness and connectors while watching live data to identify intermittent opens/shorts.
- Check continuity from sensor connector back to the ABS module pins and verify there are no shorts to battery or ground.
- If sensor and wiring check good but fault persists, swap sensor with the same-position sensor (if feasible) or substitute a known-good sensor to isolate sensor vs. module/wiring.
- Repair or replace damaged components (sensor, tone ring, wiring, connector). After repair clear codes, perform test drive and re-check for reoccurrence.
- If wiring and sensors are good and problem persists, test/inspect ABS module power/ground and communication lines or consult manufacturer-specific diagnostics for module faults.
Likely causes
- Corroded or wiggling connector at the wheel hub leading to intermittent signal.
- Sensor damaged by road debris or during wheel service.
- Tone ring tooth damage or missing teeth causing erratic waveform.
- Wire chafed where it passes through suspension or near the wheel hub.
- Failed active sensor electronics (no Vref or no square-wave output).
Fault status
Status
C0300 — Wheel Speed Sensor Circuit Malfunction (ABS). Stored when the ABS control module detects a missing, implausible, intermittent, or out-of-range wheel speed sensor signal from one wheel. Possible causes include sensor failure, wiring/connector issues, damaged tone ring, poor sensor supply/ground, or ABS module fault.
Repair difficulty: Medium
Diagnostic time: 1–3 hours
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Repair manuals
Manual library for HUMMER
69
Browse 69 HUMMER manuals: repair procedures, diagnostics, wiring diagrams, component locations, service data and Labor Times by year, model and trim.
HUMMER
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