P0502: Vehicle Speed Sensor A Circuit Low Input
What to do
Driveable with an unreliable speedometer. Automatic transmissions may shift harshly.
What this code means
The speed sensor circuit is reading low, generally a short to ground or an open in a circuit that idles high. The sensor lives underneath the vehicle on the gearbox, so its wiring takes road spray, salt and heat — the harness deserves inspection before the sensor is replaced.
Likely causes
Start here
- Signal wire shorted to ground · moderate
- Faulty vehicle speed sensor · moderate
- Road damage to underfloor wiring · moderate
- Corroded or loose connector · easy
Symptoms
Components involved
Information, not instruction
CarGeek is a reference, not a service manual. Its pages are written from public sources and from what other people have found, never from a manufacturer's own service information, so they can be wrong or incomplete for your particular vehicle. Some of what they describe carries real risk: high voltage, fuel under pressure, stored energy, hot and moving parts.
Have anything you intend to act on checked by a trained person against the manufacturer's own procedure for your vehicle. Nothing here replaces that procedure.
Community experience
Be the first to write this up
Nothing posted about this yet. Whatever you found is worth writing down — even a dead end saves someone the same afternoon.
What makes one worth reading:
- The car — make, model, year and engine. The same fault behaves differently on each.
- What you measured, not only what you replaced.
- What actually fixed it — or that nothing did, which is worth knowing too.
Sign in or create an account to add what you found about P0502.