P0502: Vehicle Speed Sensor "A" Circuit Low Input
Quick Answer
Not safe to drive
P0502 means the ECU is detecting a voltage on the vehicle speed sensor circuit that is lower than expected, typically because the signal wire is shorted to ground, the sensor has failed open, or the connector has lost contact. On vehicles that use the ABS wheel speed sensors as the primary speed input, P0502 usually accompanies an ABS wheel speed code.
- Severity
- Moderate · Electrical
- Estimated repair cost
- From €60 to €650+, varies by vehicle
Scan your own car in about 60 seconds: see whether P0502 is really what it has, how urgent it is, and what the fix should cost. Free on iPhone and Android with an ELM327 adapter (Bluetooth LE on iPhone).
Get Skanyx freeWhat does P0502 mean?
P0502 is a electrical-related diagnostic trouble code classified as moderate severity.
What are the symptoms of P0502?
- Speedometer reads zero even while driving
- ABS and traction control warning lights on
- Cruise control will not engage
- Automatic transmission shifts harshly or stays in a single gear
- Check engine light on
What causes P0502?
Open or shorted-to-ground wiring on the speed sensor signal circuit
: high
Failed vehicle speed or ABS wheel speed sensor
: high
Disconnected or corroded sensor connector
: medium
Missing or sheared reluctor ring
: low
Is it safe to drive with P0502?
No - address this immediately. The ECU is reading a vehicle speed signal that is below the expected threshold, which usually means zero signal or a shorted-to-ground circuit. Speedometer, ABS, and transmission shift quality are affected. Drive only as far as needed to reach a workshop.
How do you diagnose P0502?
- Read all stored codes. Companion ABS wheel speed codes (C-codes) usually point directly to the failed circuit
- Locate the suspect sensor and inspect the connector for water, corrosion, and damaged pins. Reseat the connector and clear the code to see if it returns
- With ignition off, measure resistance from the sensor signal pin to chassis ground. A near-zero reading confirms a short to ground in the wiring or the sensor
- Backprobe the sensor connector with the engine running and the wheels spinning. A Hall-effect sensor should switch between roughly 0 V and 5 V; a magnetic sensor should produce a small AC waveform that grows with speed
- If the wiring and sensor are healthy, inspect the reluctor ring for missing teeth, cracks, or a sheared press fit
How much does P0502 cost to fix?
| Repair | Parts Cost | Labor Cost | Total Estimate | DIY Difficulty |
|---|---|---|---|---|
| Repair sensor wiring or connector | €10–€40 | €50–€150 | €60–€190 | Moderate |
| Replace vehicle speed or ABS wheel speed sensor | €30–€120 | €40–€100 | €70–€220 | Moderate |
| Replace wheel bearing with integrated reluctor ring | €80–€250 | €150–€400 | €230–€650 | Professional |
Prices estimated as of October 2026. Costs vary by region, vehicle, and shop.
P0502 on specific vehicles
P0502 on BMW
BMW 3 Series
P0502 on Volkswagen
Volkswagen Golf
Ford
Ford Focus
2005-2022
Mk2 and Mk3 Focus suffer rear bearing magnetic encoder failures. When the encoder ring inside the bearing demagnetises or cracks, the sensor stops producing a signal entirely and the ECU logs P0502. The fix is a new rear bearing assembly with integrated ring.
P0502 on Opel
Opel Astra
Related diagnostic codes
Common questions about P0502
- What does low input on a speed sensor circuit actually mean?
- It means the ECU is seeing a voltage that is below the normal range on the signal wire, usually because the wire is shorted to ground, the sensor has failed open, or the connector is disconnected. The ECU interprets this as no movement and triggers P0502.
- Why is my speedometer stuck at zero?
- The most common cause is a dead vehicle speed or ABS wheel speed sensor, or a broken signal wire between the sensor and the ECU. On cars that share the ABS signal with the speedometer, a single failed sensor can knock out both.
- Can I drive a short distance with P0502?
- Mechanically yes, but the speedometer will not work and ABS plus traction control will be disabled. A car without a working speedometer or ABS is a roadworthiness problem in its own right, and the rules on driving it differ by country. Drive only as far as needed to reach a workshop and keep speeds low.
- Is P0502 always a sensor problem?
- No. Wiring damage is just as common, especially where the harness runs through the wheel arch or near the gearbox. Always test the wiring before replacing the sensor or you may swap parts without fixing the fault.