Code
P1390
HUMMER
P — Powertrain
Wheel Speed Sensor 1 - G - Sensor Circuit
AI status
Completed
Completed
100%
Causes
- Open or intermittent wiring between sensor and ABS/TCM module
- Short to ground on the sensor signal wire
- Short to battery/ignition voltage on the signal or reference wire
- Corroded, bent or disconnected sensor connector or pin(s)
- Failed wheel speed sensor (Hall or inductive)
- Damaged or missing tone ring/reluctor (broken teeth, heavy rust/debris)
Symptoms
- ABS warning lamp illuminated
- Traction/stability control warning light (VSC/TC) illuminated
- Reduced or disabled ABS/traction control functionality
- Inconsistent or no wheel speed reading for affected wheel (ABS events or braking feel may change)
- Possible speedometer/odometer anomalies if vehicle uses wheel speed input
What to check
- Read freeze frame and all stored DTCs with a scan tool; note which wheel is identified as Sensor 1 if available
- Visually inspect sensor wiring, connector and tone ring for damage, corrosion or foreign material
- Check for loose or damaged pins at wheel harness and ABS module connector
- Back-probe the sensor connector with ignition ON and engine OFF to check for reference voltage (if active sensor) and ground
- Measure sensor resistance with multimeter (engine off) and compare to spec or opposite wheel
- Spin the wheel and measure AC output (passive sensor) or signal waveform (active sensor) with oscilloscope while cranking/spinning and compare to other wheel
Signal parameters
- Passive (inductive) sensor: shows AC voltage whose frequency and amplitude increase with wheel speed; typical DC resistance varies by sensor type (commonly several hundred to a few thousand ohms)
- Active (Hall/VR) sensor: has a reference 5V (or ignition reference), ground, and a digital/square-wave or pulse output between 0–5V proportional to wheel speed
- Waveform: consistent, repetitive pulses while wheel spins; absent, erratic, or clipped waveform indicates fault
- No universal numeric spec—refer to vehicle service manual for exact resistance, reference voltage and waveform levels
Diagnostic algorithm
- Safety first: park on level ground, chock wheels, and support vehicle securely on jack stands before working at a wheel.
- Retrieve all codes and freeze-frame data; note whether code identifices a specific wheel.
- Perform visual inspection of sensor, wiring, harness grommets, and tone ring for damage or contamination.
- With connector disconnected, measure sensor DC resistance (for passive) or check reference voltage and ground (for active) and compare to spec or opposite wheel.
- Reconnect and back-probe signal while spinning wheel (use wheel lift or run at low vehicle speed) to observe AC/signal waveform with oscilloscope or scan tool; compare amplitude and frequency to known-good wheel.
- Perform wiggle test on harness while monitoring live data to detect intermittent connections.
- Check for continuity from sensor signal wire to ABS module pin and check for short to ground or battery voltage using multimeter.
- Inspect tone ring for missing/broken teeth, heavy rust, magnetic debris, or excessive air gap; repair/replace as needed.
- Repair or replace wiring/connector/sensor as indicated by tests. If wiring and sensor test good, suspect ABS module driver fault and pursue module-level diagnosis.
- Clear codes and test drive to confirm repair; recheck for reappearance of code.
Likely causes
- Wiring problem at connector (corrosion/pin pushed out)
- Failed wheel speed sensor (more common than module failure)
- Damaged tone ring or excessive air gap caused by bearing/hub wear
Fault status
Status
Stored when the ABS/traction control module detects an abnormal or no signal on Wheel Speed Sensor 1 (circuit G): open, shorted, intermittent, or implausible reading. Typically illuminates ABS/traction warning lamps and may disable related systems.
Repair difficulty: Medium
Diagnostic time: 1.0 - 2.5 hours
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Repair manuals
Manual library for HUMMER
138
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