Code
P1391
HUMMER
P — Powertrain
Wheel Speed Sensor 1 - G - Sensor Circuit Performance
AI status
Completed
Completed
100%
Causes
- Open or shorted wiring to wheel speed sensor 1 (G)
- Corroded, loose or damaged sensor connector/pins
- Failed wheel speed sensor (Hall-effect or variable reluctor)
- Damaged or missing tone/reluctor ring on hub or axle
- Excessive sensor air gap or incorrect sensor mounting
- Intermittent contact from bent pins or water ingress
Symptoms
- ABS, Traction Control, or VSC warning lamp illuminated
- Inoperative or intermittent ABS/traction control operation
- Possible speedometer or cruise control irregularities (if vehicle uses same speed source)
- Brake pulsation during ABS events or reduced ABS functionality
- Diagnostic trouble codes stored for wheel speed sensors
What to check
- Read live data with a capable scan tool: monitor wheel speed sensor 1 (G) while rotating wheel
- Inspect sensor connector for corrosion, bent pins, moisture and secure mating
- Visually inspect tone/reluctor ring for missing teeth, heavy rust or debris
- Inspect wiring along suspension/steering for abrasion, broken wires, or pinch points
- Check ABS/traction related fuses and module grounds for good continuity
- Perform resistance and/or AC voltage checks at sensor per vehicle specification
Signal parameters
- Passive (variable-reluctor) sensor: produces AC sine wave; low-speed amplitude typically ~0.1–1.5 Vpp and frequency increases with wheel speed; DC resistance commonly in the range ~500–2000 Ω (vehicle dependent)
- Active (Hall/VR with electronics) sensor: square wave or pulse output ~0–5 V referenced to sensor ground; reference voltage often 5 V or pull-up within module; current draw typically
- Expected waveform: clean alternating pulses (passive) or stable digital square pulses (active) with consistent amplitude and frequency between wheels at equal speeds
- Typical fault signatures: no output, constant voltage, excessive noise, missing pulses or intermittent drops to 0 V
Diagnostic algorithm
- Connect a scan tool and record DTCs and live data for all wheel speed sensors; note differences between wheel sensors at low and high speed.
- Visually inspect sensor 1 (G) connector and wiring for corrosion, bent pins, broken wires, and moisture; repair or reseal as required.
- With ignition on (engine off) backprobe sensor connector: for active sensors check for reference voltage (≈5 V) and ground; for passive sensors measure DC resistance across sensor terminals and compare to specs.
- Rotate wheel by hand (or carefully raise wheel) and observe waveform with oscilloscope or multimeter AC setting: passive = AC sine pulses; active = square pulses; compare amplitude/frequency to opposite wheel.
- Inspect tone/reluctor ring for damage, missing teeth, heavy rust or debris; clean or replace if required. Also inspect wheel bearing and hub for play or metal debris.
- If wiring or connector suspect, perform continuity and resistance checks from sensor connector to ABS module harness connector; repair any opens/shorts.
- Clear codes and perform a road test while monitoring live sensor data to confirm the fault is resolved or to catch intermittent failures.
- If sensor, wiring and tone ring check good but fault persists, check ABS module power, ground and internal fault codes; consider module diagnosis by qualified technician.
Likely causes
- Corroded connector at the sensor or behind the hub
- Broken or chafed wire in the harness near suspension or steering knuckle
- Contaminated or mechanically damaged sensor tip
- Missing/broken tooth(s) on the tone ring or heavy rust build-up
- Poor ground or blown fuse feeding ABS/traction electronics
Fault status
Status
Wheel Speed Sensor 1‑G circuit performance fault detected (ABS/traction sensor).
Repair difficulty: Medium
Diagnostic time: 0.5-2.0 hours
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