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DTC codes / GM codes / P1391

P1391 · GMWheel Speed Sensor 1 G-Sensor Circuit Performance

This code means the powertrain control module (PCM) has detected an abnormal performance signal from the wheel speed sensor circuit that also provides a G-sensor (acceleration) signal on your GM vehicle. The PCM compares the expected signal pattern against what it actually receives and sets P1391 when the signal is erratic, out of range, or missing for a calibrated period.

SystemPowertrain
Code typeGM specific
SeverityMedium
Fix difficultyIntermediate
AreaIgnition system and misfire

Symptoms you may notice

  • Anti-lock brake system (ABS) warning light illuminated on the dashboard
  • Traction control or stability control warning light on, with the system disabled
  • Speedometer needle fluctuating or reading zero intermittently
  • Erratic or harsh transmission shifting due to incorrect vehicle speed data
  • Often no symptoms besides the warning light, especially if the fault is intermittent

Common causes, most likely first

  1. Damaged or corroded wheel speed sensor wiring harness near the hub or along the suspension
  2. Faulty wheel speed sensor itself, often due to debris or metallic particles on the sensor tip
  3. Excessive air gap between the sensor and the tone ring caused by rust jacking or a worn hub
  4. Damaged or dirty tone ring (reluctor wheel) with missing teeth or heavy rust
  5. Poor electrical connection at the sensor pigtail or the ABS control module connector
  6. Internal fault in the ABS control module affecting the sensor signal processing

How to diagnose and fix it

  1. Inspect the wheel speed sensor wiring and connector at the affected wheel for chafing, corrosion, or loose pins
  2. Remove the sensor and clean the mounting surface and sensor tip of metallic debris and rust
  3. Check the tone ring for cracks, missing teeth, or heavy rust and replace the hub or axle if damaged
  4. Measure the air gap between the sensor and tone ring with a feeler gauge and compare to specification
  5. Perform a resistance and AC voltage output test on the sensor while spinning the wheel by hand
  6. Use a scan tool to view live wheel speed data for all four wheels and compare readings while driving
  7. If all sensor and wiring checks pass, test the ABS control module circuits and replace the module if internal failure is confirmed

What most technicians miss on P1391

  • A common misdiagnosis is replacing the wheel speed sensor when the real problem is a rust-swollen hub that has pushed the tone ring away from the sensor, changing the air gap.
  • Metallic debris from a worn brake rotor or hub bearing can stick to the magnetic sensor tip and cause an erratic signal that mimics a failed sensor.
  • The G-sensor function in this circuit means that a faulty sensor can also affect stability control and hill-start assist even when the ABS light is the only warning shown.
  • Intermittent P1391 codes often appear only during certain driving conditions such as sharp turns or rough roads, so a static test at the shop may show nothing until the harness is flexed.
  • Corrosion inside the ABS module connector can distort the sensor signal without any visible damage to the sensor or its wiring, so always back-probe the module side.

Can I keep driving with P1391?

You can usually drive the vehicle with P1391 set, but the ABS and stability control systems may be disabled, so avoid hard braking or slippery conditions until the fault is repaired. If the speedometer is erratic or the transmission shifts harshly, keep speeds low and get it diagnosed promptly.

Tools that help

Tools we recommend are in the Auto Veteran shop on Amazon. As an Amazon Associate we earn from qualifying purchases.

Guidance is general and written for GM vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.

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