What does it mean?
P1390 is a Powertrain (engine, transmission, fuel system) fault code. It indicates: Wheel Speed Sensor Circuit .
Symptoms
- MIL on, often with ABS and traction control warning lamps
- Speedometer erratic, dropping out or reading zero
- ABS or traction control activating for no reason at low speed
- Cruise control unavailable
- Automatic transmission may shift harshly or hold a gear
Likely causes
- Open, shorted or chafed wheel speed sensor wiring, usually where it flexes with the suspension
- Metal debris on the sensor tip or a cracked and rusted tone ring
- Corroded connector or water trapped inside it
- Excessive air gap caused by a worn wheel bearing
- Failed wheel speed sensor
- Missing speed data on the network because of a module or bus fault
- Mismatched tyre sizes or an incorrect final drive giving implausible speed values
How to fix it
- Read all four wheel speed values in live data and compare them while driving slowly
- Inspect the suspect sensor harness where it flexes with the suspension and steering
- Clean the sensor tip and inspect the tone ring for missing, rusted or damaged teeth
- Measure sensor resistance or output and scope the signal while turning the wheel by hand
- Check wheel bearing play, which directly changes the sensor air gap
- Repair connector corrosion and any damaged wiring found
- Replace the sensor or tone ring as needed and confirm all four signals now track together