P0502 - VEHICLE SPEED SENSOR (VSS) - LOW INPUT
Description of DTC code P0502
The P0502 OBDII diagnostic code is configured when the PowerTrain Control Module finds an input signal of the VSS Sensor (Vehicle Speed Sensor) which results to be below the set limit.
Input data from the VSS sensor are used by the PCM and compares them with input data of the electronic brake system control module to control and regulate the patterns of transmission changes. In general, Vehicle Speed Sensors (VSS) are geared to the transmission axis. While the output shaft rotates, the gear drives a reluctant wheel on the sensor. This wheel has teeth that stopping a magnetic field when passing in front of a permanent electromagnet. The PCM interprets these interruptions like a wave, which means an electric voltage. That voltage is known as a signal, which changes according to the variations of the wave frequency that generate the speed sensor.
Because the actual vehicle speed is calculated by using the speed at which the VSS sensor rotates, as there is a fault in the sensor circuit, the PCM receives an input signal lower than what it expects to see, resulting in an imbalance between the input data of the VSS Sensor and the data provided by other secondary speed sensors. If this occurs, this code is established and the Check Engine light illuminates on the board.
Symptoms of fault code P0502
- MIL light (engine malfunction) on.
- Incorrect speedometer operation.
- Transmission change patterns are irregular.
- Other transmission codes established.
- ABS system inoperability.
Causes of OBD2 P0502
The DTC code P0502 OBD2 is set due to the following:
- There may be an excessive accumulation of metal debris in the Speed Sensors.
- Cable system or Speed Sensor connectors in poor condition.
- VSS Sensor reluctor ring with damages.
- The VSS Sensor may be defective.
Possible solutions of the DTC code P0502
To solve the problems of the P0502 OBDII fault code you should consider the following:
- Look for Technical Service Bulletins (TSB).
- Visually inspect the wires and electrical connections of the VSS Sensor. If there are defects in these components, proceed to make the necessary repairs.
- Check the Speed Sensor for metal debris. If so, remove the waste.
- Check the good condition of the sensor's reluctor ring.
- Locate the VSS Sensor circuit and with a DVOM perform resistance tests. Check with the source of information of the manufacturer to know the recommended values. Change the sensor if the obtained readings do not coincide with the specifications.
- Use an oscilloscope to retrieve live data from the VSS Sensor. If you see inconsistencies in the pattern, you must make the respective diagnosis.
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