Vehicle Speed Sensor A Range/Performance Problem
This code indicates a problem with the vehicle speed sensor's performance or signal.
Heads up: this code wasn't in our hand-written library yet, so DiagCoach AI built this page on the fly. Double-check critical specs against service info before condemning parts.
What it means (plain English)
The vehicle speed sensor (VSS) is signaling that the speed it's reading is out of its expected range, which usually means it's giving an incorrect speed or no speed at all.
What the computer is actually seeing
The PCM expects the VSS to output a voltage signal proportional to the vehicle speed. A properly functioning sensor should send signals between 0.5V (0 km/h) and about 5V (around 140 km/h) based on the speed and type of vehicle.
What a healthy reading looks like
Typical voltage from the VSS while driving should be between 0.5V to 5V, depending on speed. If the voltage remains at 0V or goes beyond the limits for more than a few seconds, the PCM will trigger this code.
Guided diagnostic — the DiagCoach way
Don't just throw parts at it. Walk through these in order — each step tells you whether to keep going or stop and fix what you found.
- 1Check the vehicle speed sensor wiring for damage or corrosion; repair as needed. Decision: If wiring is intact, proceed to step 2.
- 2Inspect the connector at the vehicle speed sensor for corrosion or loose connections; repair if necessary. Decision: If the connector is good, proceed to step 3.
- 3Using a multimeter, measure the output voltage of the VSS while the vehicle is moving; it should be between 0.5V to 5V. Decision: If voltage is within range, suspect PCM issues; if voltage is out of range or 0V, replace the VSS and retest.
- 4If replacing the VSS did not solve the issue, check for any blown fuses related to the VSS and inspect the wiring harness for short circuits. Decision: Replace any blown fuses or damaged wiring.
Common causes
- Faulty Vehicle Speed Sensor (VSS)
- Wiring issues or faulty connectors
- Faulty PCM (rare)
- Damaged reluctor ring (if applicable)
- Low transmission fluid levels
Typical repair cost
$100-$300
Related codes
Frequently asked questions
Is it safe to drive with P0502?
It is generally drivable but may affect transmission shifting and stability. Keep an eye on performance.
Will this code come back after clearing it?
If the underlying issue is not resolved, the code will likely return after clearing.
Why does this code sometimes pair with other codes?
Other codes often indicate related sensor or wiring issues that can affect vehicle speed reporting.
Working a real vehicle right now?
Let DiagCoach walk you through it live with your specific symptoms, vehicle, and what you've already checked.
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