P0502 Speed sensor: signal or voltage too low (vehicle speed, "A")

By: Diagno editorial team · Updated: 2026-10-15

P0502 means: Speed sensor: signal or voltage too low (vehicle speed, "A"). The speed sensor gives the computer the vehicle speed. Drive gently and have the car checked soon. The repair usually costs about €50–300 in Estonia. The most common cause: connector loose, damp or corroded.

What it means

The speed sensor gives the computer the vehicle speed. If the signal drops out, the speedometer, gear changes, ABS or cruise control may misbehave. The signal voltage is too low. Usually a wire is broken, a connector is loose or a wire is shorted to ground.

What you may notice

• Speedometer dead or jumping
• Automatic gearbox shifts wrongly
• Cruise control doesn't work
• Engine light on

What could be wrong

1. 1Connector loose, damp or corroded
2. 2Wire broken or shorted to ground
3. 3Faulty sensor
4. 4Engine computer fault (rare)

Repair difficulty: Moderate

What you can check yourself

First look at the connector and wiring: anything loose, melted or green with corrosion? Check whether the speedometer works. If the ABS light is also on, the fault is probably in a wheel sensor. You can check the simple things yourself, but the repair is best done in a workshop.

How we fix it

1. We read the fault data on the diagnostic tool and check whether the fault is constant
2. We measure the circuit's supply, ground and signal
3. We repair the wire or replace the connector
4. If the wiring is fine, we replace the sensor

Standard SAE description: Vehicle Speed Sensor "A" Low Input