Powertrain, generic · Vehicle speed, idle control and auxiliary inputs

P0502 Vehicle Speed Sensor A Circuit Low

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modePossible

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.

Likely causes

Speed or output speed sensor faulty
Wire open or shorted to ground, connector corroded
ABS module sends no speed signal
Tone wheel damaged or sensor dirty

Symptoms

  • Check engine light on
  • Speedometer dead or jumping
  • Cruise control not working
  • Automatic shifts harshly or wrongly

Repair estimate

DifficultyMediumDIY possible
Parts and labour€60–350
Time0.5–2 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

vehicle speed sensorabs modulesensor wiringengine control module

Related codes

P0500P0501P0503P0722P0720

References: gsi.ext.gm.com, gsi.ext.gm.com, saabwisonline.com, saabwisonline.com.