P0502
Vehicle Speed Sensor A Circuit Low
The primary vehicle speed sensor (VSS A) reports a signal voltage below the plausible lower limit. With no usable speed signal the ECU loses cruise control, gear-shift logic and certain anti-stall functions.
- Check engine light: Yes
- Emissions related: No
- Repair difficulty: easy
Common causes
Ordered by how often each turns out to be the cause.
- Signal shorted to groundCommon
- Sensor internal shortPossible
- Connector pins corroded - high contact resistanceLess likely
Parts involved
- Vehicle Speed Sensor A
- VSS Wiring
P0502 is a generic OBD-II code defined by SAE J2012. Exact wording and diagnostic procedure vary by manufacturer and model. Code definitions are drawn from the public-domain OBDex dataset; the workshop notes are our own.