P0502: Vehicle Speed Sensor Low Input
The P0502 code indicates that the Powertrain Control Module (PCM) has detected a low or missing signal from the vehicle speed sensor (VSS). This sensor monitors the rotational speed of the transmission output shaft or differential to calculate vehicle speed. A low input means the voltage signal is below the expected range, often due to a faulty sensor, wiring issues, or a damaged reluctor ring.
01. Most Common Causes
- Faulty vehicle speed sensor
- Damaged or corroded wiring/connectors to VSS
- Broken or missing reluctor ring
- Internal transmission or differential mechanical failure
02. Symptoms You Will Notice
- Speedometer not working or erratic
- Check Engine Light illuminated
- Transmission shifting harshly or at wrong times
- Cruise control inoperative
03. Step-by-Step Diagnosis
Step 1: Scan for codes and record freeze frame data.
Step 2: Visually inspect VSS wiring and connector for damage or corrosion.
Step 3: Test VSS resistance and AC voltage output while spinning the wheel or driveshaft.
Step 4: Check reluctor ring for damage or debris.
Step 5: Verify PCM signal processing with a scan tool.
04. Commonly Affected Makes
05. Frequently Asked Questions
Is it safe to drive with this code?▼
It is not recommended to drive long distances as the transmission may shift improperly, causing further damage. Limited local driving may be possible but with caution.
How much does it cost to fix?▼
Typical repair costs range from $50 to $150 for a new sensor, plus labor if installed by a shop. Wiring repairs may add $50-$100.