P0503 Speed sensor: signal drops out at times (vehicle speed, "A")

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

P0503 means: Speed sensor: signal drops out at times (vehicle speed, "A"). The speed sensor gives the computer the vehicle speed. Drive gently and have the car checked soon. The most common repair costs about €45–90 in Estonia, depending on make and model. 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 drops out now and then. The most common cause is a loose connector or a chafed wire.

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 · Wiring or connector repair €45–90
2. 2Wire broken or chafed · Wiring or connector repair €45–90
3. 3Faulty sensor · Sensor replacement €80–160
4. 4Engine computer fault (rare) · Control unit check and software €150–300

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" Intermittent/Erratic/High