What Does P0502 Mean?
The vehicle speed sensor circuit is producing a signal that is below the minimum expected voltage threshold. The PCM is detecting a low or no-signal condition from the VSS when it expects the vehicle to be moving. The driver will likely see a speedometer that reads zero or significantly lower than actual speed, and the transmission may not shift properly.
Common Causes
30%
Open or shorted circuit in VSS wiring harness
30%
Failed vehicle speed sensor with low or no output
20%
Poor ground connection at the VSS or PCM
12%
Excessive air gap between VSS and reluctor wheel
8%
PCM input driver failure on the VSS circuit
Diagnostic Steps
1
Check freeze frame data to confirm the vehicle was in motion when the code set — verify engine RPM was above idle and transmission was in gear.
2
Backprobe the VSS connector with the sensor connected and monitor voltage output while slowly rotating the drive wheel — you should see a pulsing signal (AC or square wave depending on sensor type).
3
Measure continuity and resistance of the VSS signal wire from the sensor connector to the PCM connector pin — resistance should be less than 5 ohms with no opens.
4
Check for proper reference voltage at the VSS connector (typically 5V or 12V) with the key on, engine off. If missing, trace the reference circuit back to the PCM.
5
Verify the VSS air gap is within specification (typically 0.5-1.5mm). Reposition sensor if adjustable, or check for excessive reluctor wheel runout.
Estimated Repair Cost
$60 - $300
Parts + labor, varies by vehicle and location
The vehicle speed sensor circuit is producing a signal that is below the minimum expected voltage threshold. The PCM is detecting a low or no-signal condition from the VSS when it expects the vehicle to be moving. The driver will likely see a speedometer that reads zero or significantly lower than a...
The most common cause of P0502 (Vehicle Speed Sensor Circuit Low Input) is: Open or shorted circuit in VSS wiring harness
Typical repair costs for P0502 range from $60 to $300, depending on the vehicle, location, and whether you do it yourself or go to a shop.
The vehicle can be driven carefully, but speedometer accuracy is compromised. The transmission may exhibit harsh or delayed shifts. ABS and traction control may be partially disabled. Avoid highway driving until the issue is resolved, as speed-dependent safety systems may not function correctly.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P0502 to identify the root cause.
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Quick Info
Category
Powertrain
System
Vehicle Speed / Transmission Control
Difficulty
Type
Generic (SAE)
Recommended Tools
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