Fault code P0502 – a step-by-step guide to diagnosing and fixing it

Error code P0502 is displayed and the check engine light is on - what does this mean?

The OBD/EOBD system detects an input value from the vehicle speed sensor (VSS) that is too low. This DTC P0502 means that the engine control unit is receiving no signal or too weak a signal from the speed sensor. This error code may have slightly different names for different manufacturers, but always refers to problems with the speed measurement.

What causes can this error code have?

• Defective vehicle speed sensor (VSS)
• Damaged or corroded cable connections to the speed sensor
• Loose or dirty plug connections
• Defective ABS control unit or wheel speed sensor
• Interrupted wiring between sensor and control unit
• Worn gear wheels on the gearbox or differential
• Faulty ground connection of the sensor
• Defective instrument panel or speedometer

What symptoms occur in parallel with fault code P0502?

• Speedometer problems: The speedometer shows no or incorrect values
• ABS malfunctions: The anti-lock braking system is not working properly
• Cruise control failure: The cruise control system no longer works
• Shifting problems: Shifting problems may occur with automatic transmissions
• Engine performance: Reduced engine power or rough running
• Additional fault codes: Additional DTCs related to ABS or transmission

How to fix the problem of trouble code P0502?

• Repairing trouble code P0502 requires a systematic approach to identify the source of the fault.
• Checking and replacing the vehicle speed sensor on the transmission, as this is often the main cause of fault code P0502
• Check and repair all cable connections between the VSS and control unit, including cleaning corroded contacts and replacing damaged cables
• Checking the plug connections for tightness and cleanliness, followed by contact spray treatment to improve signal transmission
• Diagnosis and replacement of defective ABS wheel speed sensors, which can act as an alternative speed source
• Repair of the speed sensor ground connections by cleaning the ground points and ensuring stable grounding
• Replacing worn gears on the gearbox or differential that are required for signal generation of the VSS