P0502 means Vehicle Speed Sensor A Circuit Low Input. The vehicle speed sensor signal is low or missing while the vehicle is moving. It is a generic OBD-II code, so the definition is the same on any make, but the most likely cause varies by engine; confirm with a scan tool and the service information for your vehicle before buying parts.
What P0502 means
Most engine sensors receive a 5-volt reference and return a signal between roughly 0 and 5 volts. Codes ending in circuit high or circuit low usually point to an electrical fault: an open circuit, a short or an unplugged connector. Range/performance codes mean a signal is present but disagrees with what the computer expects from the other sensors, which more often points to a dirty sensor, an air leak or a mechanical problem.
P0502 symptoms
- Speedometer not working or erratic
- Harsh or erratic shifting
- Cruise control not working
- ABS or traction lights on some vehicles
Common causes of P0502
- Failed speed sensor
- Wiring shorted or open
- Debris on the sensor tip
- Damaged sensor drive gear or tone ring
How to diagnose P0502
- Watch the speed signal on a scan tool while driving
- Inspect the sensor and connector
- Check the wiring for damage
Can you drive with P0502?
Usually yes, with care; shifting and the speedometer may be affected.
P0502 tips
On some vehicles, the speed signal comes from the ABS wheel speed sensors; read the ABS module codes as well.
Will P0502 clear itself?
If the fault stops, the computer turns off the check engine light by itself after several drive cycles without seeing it again, and the code stays in memory as history for a while. Clearing P0502 with a scan tool after a repair is fine, but if the cause is still there the code returns, sometimes within one drive. Disconnecting the battery also clears codes on most vehicles, but it erases learned fuel trims and idle settings as well.
Related codes
| Code | Meaning |
|---|---|
| P0500 | Vehicle Speed Sensor A Malfunction |
| P0501 | Vehicle Speed Sensor A Range/Performance |
| P0503 | Vehicle Speed Sensor A Intermittent/Erratic/High |
Guides that help
When it is more than a sensor
Sensor codes are usually fixed with a sensor, a connector, wiring or a leak repair rather than major parts. If testing turns up internal engine trouble instead, see how to tell if an engine is blown and compare engines by code on our engines page.
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