P0502 Diagnostic Trouble Code: Vehicle Speed Sensor “A” VSS Low Input

Fault code P0502 is called “Vehicle Speed Sensor “A” VSS Low Input” but in different programs it may be called differently. This fault designation applies to all vehicles equipped with OBD-II.

Technical description and explained code P0502

This diagnostic trouble code (DTC) is a generic transmission code. Error P0502 is considered a general code because it applies to all makes and models of vehicles. Although the specific repair steps may vary slightly depending on the model.

P0502 Diagnostic Trouble Code: Vehicle Speed Sensor "A" VSS Low Input

Fault code P0502 OBD2 means that the transmission control module (PCM) has detected a low voltage input signal from the vehicle speed sensor (VSS) “A”. The “A” designation usually refers to the main VSS in systems that use multiple vehicle speed sensors.

The vehicle speed sensor (VSS) transmits information to the ECM (Engine Control Module) about the vehicle speed. For display by the speedometer and the odometer. It does this by providing a signal of 4 pulses for each revolution of the rotor shaft, which rotates the output shaft through a driven gear. Typically, the VSS is an electromagnetic sensor that uses the rotation to send a signal to the ECM.

The VSS is mounted in the gearbox housing in a position so that pulses from the box can pass in close proximity to it. When the box pulses pass the VSS solenoid tip. Notches and grooves are used to quickly close and interrupt the circuit.

These manipulations are recognized by the PCM module as the output speed of the transmission or vehicle speed. Which allows us to see the usual speed display on the speedometer.

Symptoms of vehicle malfunctions

The main signal that an error P0502 has occurred is the Malfunction Indicator Lamp (MIL) is also known as the CheckEngine Light.

It can also be warning signs such as:

  1. The vehicle’s anti-lock braking system (ABS) and traction control system (TCS) are disabled.
  2. The (ABS) or brake warning lights on the instrument panel may be illuminated.
  3. The speedometer or odometer may not work correctly or may not work at all.
  4. The vehicle’s rev limiter may be lower than normal.
  5. The automatic transmission may have problems shifting gears.
  6. Other symptoms may be present.

Fault code P0502 is medium in severity. It indicates that the car speed sensor is not working properly. The vehicle’s anti-lock braking system (ABS) may be disabled.

Factors that can cause this error code

The error code P0502 can mean that one or more of the following problems have occurred:

  • The vehicle’s speed sensor “A” (VSS) is not reading properly and therefore has insufficient readings.
  • Excessive accumulation of metal debris on the speed sensor.
  • The wire leading to the vehicle’s speed sensor is broken or frayed.
  • Bad connection in the vehicle speed sensor (VSS) circuit.
  • The vehicle’s PCM is not properly set for the actual tire size being used.
  • Damaged speed sensor drive pinion.
  • Engine control module (ECM) may be defective.

How to fix or reset OBD-2 code P0502

Some suggested steps for troubleshooting and fix the error code P0502:

  1. First read all stored data and error codes with an OBD-II scanner.
  2. Then clear the error codes and test drive the vehicle to see if there is a problem.
  3. After that, check the vehicle’s speed sensor and all relevant wires for wear and damage.
  4. Also check for a speed sensor signal when the car is running with a scanner.
  5. If there are no problems described above, check the voltage of the vehicle’s speed sensor with a multimeter.

Diagnose and repair of problems

It’s a good idea to first look up the Technical Service Bulletins (TSB) for your particular make of car with error P0502. If the problem is already described, following the instructions can save you time and money in diagnosing and fixing the problem.

Visually inspect all wiring and connectors leading to the speed sensor. Look carefully for abrasions, bare wires, or broken wires. Also look for melted or otherwise damaged areas. Repair if necessary.

The location of the sensor depends on your vehicle, it is not always installed in the box. It may be on the rear axle of the transmission or the wheel hub (brake) assembly.

If there is nothing wrong with the wiring and connectors, then check the voltage on the speed sensor. Again, the exact procedure will depend on your make and model of vehicle. In all likelihood it is the problem, so replace the sensor.

On which vehicles does this problem occur most frequently

Fault code P0502 can occur on different vehicles but there are statistics on which brands this occurs most often. Here is a list of some of them:

  • Cadillac
  • Chevrolet (Aveo, Cruze, Impala, Lanos)
  • Citroen (C3, C5)
  • Daewoo (Gentra, Nexia)
  • Geely
  • Honda
  • Hover
  • Hyundai
  • Isuzu (Rodeo)
  • Lifan (Solano, X60)
  • Mitsubishi (L200, Pajero, Strada)
  • Nissan
  • Opel
  • Peugeot (307)
  • Saab
  • Subaru (Impreza)
  • Volvo

Fault code P0502 can sometimes be found with other errors. The most common are the following: P0137, P0151, P0157, P0300, P0500, P0501, P0503, P1125, P1133, P1153, P1312, P1331.

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