P0502 code meaning
Vehicle Speed Sensor A Circuit Low
Powertrain system Generic code P05xx codes Check engine light
What P0502 means
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 (gasoline) 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 deceleration 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.
P0502 at a glance
- Check engine lightYes, usually on
- Emissions testCan fail
- Limp modePossible
- Repair difficultyMedium, DIY possible
- Typical labor0.5 to 2 hours
- Clears after repairWhen cleared with a scanner
Symptoms of P0502
- Check engine light on
- Speedometer dead or jumping
- Cruise control not working
- Automatic shifts harshly or wrongly
Common causes of P0502
- Most likelySpeed or output speed sensor faulty
- Most likelyWire open or shorted to ground, connector corroded
- PossibleABS module sends no speed signal
- Less likelyTone wheel damaged or sensor dirty
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Vehicle speed sensorABS moduleSensor wiringEngine control module
What each part of P0502 means
| P | Powertrain system: engine, fuel system, ignition, emissions and transmission. |
| 0 | Generic code: it means the same on every make (SAE standard). |
| 5 | Area: vehicle speed, idle control and auxiliary inputs. |
| 02 | The exact fault in that area. |
What to do next
- Note P0502 and any other codes stored with it: several codes together often point to one cause.
- Check for loose connectors and damaged wiring around the parts the code names.
- Check open recalls for your car: some faults are fixed for free by the dealer. Enter your VIN.
- Clear the code only after the repair. If it comes back, the fault is still there.
Buying a used car? Scan it for stored codes before you pay. A recently cleared memory can hide a problem.
Questions about P0502
What does P0502 mean?
P0502 means "Vehicle Speed Sensor A Circuit Low". 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. It is a generic code, so it means the same on every make.
Is it safe to drive with P0502?
Drive gently and only to a workshop. With P0502 the car can go into limp mode (reduced power) to protect itself.
Will P0502 fail an emissions test?
Yes, it can. P0502 is emissions-related, so most inspection programs fail a car while it is stored or while the check engine light is on.
How hard is P0502 to fix?
Difficulty: medium. A typical repair takes 0.5 to 2 hours of work. A careful DIY repair is possible with basic tools and a scanner.
Will P0502 clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.