Vehicle Speed Sensor "A"

What it means

The engine computer (ECU) has detected an electrical problem in the vehicle speed sensor (VSS) circuit. The vehicle speed sensor (VSS) reports road speed to the ECU, transmission, speedometer and cruise control. The signal is missing or outside the range the ECU will accept.

Symptoms

• Check engine light on
• Speedometer not working or erratic
• Harsh or late automatic shifts
• Cruise control not working
• ABS or traction light on (if wheel sensors are used)

Probable causes

Most likely first

1. 1Damaged or unplugged connector
2. 2Open or shorted wiring
3. 3Failed sensor
4. 4Damaged reluctor (tone) ring

How to diagnose it

Work through these in order before buying parts

1. 1Record the code and its freeze frame data (speed, load, temperature when it set), then clear it and see if it comes back.
2. 2Inspect the vehicle speed sensor (VSS) connector and wiring (on the transmission output, or the ECU uses the ABS wheel speed sensors). Look for corrosion, bent or pushed-back pins, oil contamination and chafed insulation.
3. 3Watch the vehicle speed sensor (VSS) reading on live data. Compare vehicle speed on the scan tool with GPS speed while driving. It should match closely.
4. 4Check the sensor resistance (for 2-wire sensors) or power and ground (for 3-wire Hall-effect sensors). Watch the signal on an oscilloscope or graphing meter while cranking or driving; it should be a clean, regular pattern.
5. 5If the wiring checks out, test the sensor itself against the specification in a service manual.
6. 6Check for technical service bulletins (TSBs) or software updates for your make and model; some codes have known factory fixes.

Common fixes

• Repair the damaged wiring or connector
• Replace the vehicle speed sensor (VSS)
• Clear the code and test drive to confirm the repair