P0502Vehicle Speed Sensor A Circuit Low
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- Can trigger limp mode
- How the car detects it
- The vehicle speed signal A comes, depending on the maker, from a sensor on the gearbox, the transmission output speed, the wheel speeds via ABS/ESP or a CAN message; CARB explicitly names it as an input to be monitored. Despite its wording, all makers found check plausibility: the car is clearly moving (load, torque, overrun), yet the signal stays at zero. GM's 2018 tables use the transmission output speed: below 12 rpm (petrol) or 60 rpm (diesel) for 4.5 s, MIL on the first trip. Subaru (also in the Saab 9-2X) sets it below 1 km/h on overrun for over 4 s with the MIL at once; Saab's T5 after 4 s without signal above 1800 rpm. Electrical faults give the same picture.
- What you may notice
- Check engine light on
- Speedometer dead or jumping
- Cruise control not working
- Automatic shifts harshly or wrongly
- Likely causes
- LikelySpeed or output speed sensor faulty
- LikelyWire open or shorted to ground, connector corroded
- PossibleABS module sends no speed signal
- RareTone wheel damaged or sensor dirty
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Medium · Often possible to do yourself.Typical cost: €60 – €350
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.