Description of the P0502 fault code.
OBD2 Error Codes

P0502 Vehicle speed sensor “A” low input level

26.05.2022 /

P0502 – OBD-II Trouble Code Technical Description

Trouble code P0502 indicates the vehicle speed sensor input is low.

What does the fault code mean P0502?

Trouble code P0502 indicates that the vehicle speed sensor signal is low. This means that the engine control module (ECM) has detected a discrepancy between the speed readings from the vehicle speed sensor and the wheel speeds measured by other sensors.

Fault code P0502.

Possible reasons

Some possible reasons for the P0502 trouble code:

  • Defect or damage to the vehicle speed sensor.
  • Incorrect installation of the speed sensor.
  • Damage to the wiring or corrosion in the electrical circuit of the speed sensor.
  • Problems with the engine control module (ECM).
  • Incorrect functioning of other sensors such as wheel speed sensors.

What are the symptoms of a fault code? P0502?

Symptoms for DTC P0502 may include the following:

  • Speedometer malfunction: The speedometer may not work properly or show zero speed even when the vehicle is moving.
  • ABS Warning Light Malfunction: If the wheel speed sensor is also engaged, the Anti-lock Brake System (ABS) warning light may come on due to a speed data discrepancy.
  • Transmission Problems: Automatic transmission malfunction or shift changes may occur due to inaccurate speed data.
  • Limp-Home Mode: In some cases, the vehicle may go into emergency or safety mode to prevent further damage or problems.

How to diagnose a fault code P0502?

To diagnose DTC P0502, follow these steps:

  1. Checking the speedometer: Check the speedometer operation. If the speedometer does not work or shows the wrong speed, it may indicate a problem with the speed sensor or its environment.
  2. Checking the speed sensor: Check the speed sensor and its electrical connections for damage or corrosion. Also check the cable connecting the speed sensor to the engine control module (ECM).
  3. Diagnostics using a diagnostic scanner: Use a diagnostic scan tool to read the P0502 trouble code and additional data such as vehicle speed, speed sensor readings, and other parameters.
  4. Checking wheel speed sensors: If your vehicle uses wheel speed sensors, check them for damage or corrosion. Make sure the sensors are installed correctly and have proper contact.
  5. Checking wiring and electrical connections: Check the wiring and electrical connections, including ground and power, associated with the speed sensor and ECM. Make sure there are no breaks, corrosion or other damage.
  6. Checking the vacuum system (for some vehicles): For vehicles with a vacuum system, check the vacuum hoses and valves for leaks or damage, as this may also affect the performance of the speed sensor.
  7. ECM Software Check: In rare cases, the ECM software may be the cause. Check for available software updates or perform an ECM reset and reprogramming.

If after following these steps the problem persists or you are unsure of the diagnosis, it is recommended that you contact a professional auto mechanic or service center for more detailed diagnosis and repair.

Diagnostic errors

When diagnosing DTC P0502, the following errors may occur:

  • Misinterpretation of data: One common mistake is misinterpreting data received from the speed sensor or other system components. Misunderstanding of data can lead to misdiagnosis and replacement of unnecessary components.
  • Insufficient checking of electrical connections: Sometimes the error is due to insufficient checking of the electrical connections associated with the speed sensor or engine control module (ECM). Poor contacts or breaks in wiring can lead to incorrect interpretation of data.
  • Parameter mismatch: An error may occur if the parameters received from the speed sensor do not match the expected or specified values. This may be caused by a faulty speed sensor, environmental issue, or other issues.
  • Incorrect diagnosis of related systems: Sometimes, when diagnosing a P0502 code, an error may occur due to misdiagnosis or ignorance of related systems, such as the ABS system or transmission, which may also affect the performance of the speed sensor.
  • Use of inadequate equipment: The use of inadequate or uncalibrated diagnostic equipment may result in errors in data interpretation or incorrect determination of the cause of the malfunction.

To avoid these errors, it is important to follow the vehicle manufacturer's diagnostic recommendations and use the correct equipment and technique when performing diagnostics.

How serious is the fault code? P0502?

Trouble code P0502, indicating a low vehicle speed sensor signal, is serious because vehicle speed is one of the key parameters for the proper operation of many vehicle systems. Incorrect operation of the speed sensor may result in the engine management, anti-lock braking system (ABS), stability control (ESP) and other safety and comfort systems not functioning properly.

Additionally, if the speed sensor is faulty or displaying incorrect values, it can cause the transmission to malfunction, leading to potential shifting problems and increased wear on transmission components.

Therefore, the P0502 trouble code should be taken seriously and corrected as soon as possible to avoid further problems with the vehicle's performance and ensure safety on the road.

What repair will help eliminate the code? P0502

To resolve DTC P0502, follow these steps:

  1. Checking the speed sensor: First check the speed sensor itself for damage or corrosion. If the sensor is damaged or defective, it must be replaced.
  2. Checking wiring and connectors: Check the wiring and connectors connecting the speed sensor to the engine control module (ECM). Make sure the wiring is in good condition and the connectors are securely connected.
  3. Checking the speed sensor signal: Using a diagnostic tool, check the signal from the speed sensor to the ECM. Verify that the signal corresponds to the expected values ​​when the vehicle is moving.
  4. Checking for vibrations or transmission problems: Sometimes problems with the transmission or associated vibrations can cause the speed sensor to read the signal incorrectly. In this case, you should also check the condition of the transmission and possible causes of vibrations.
  5. Updating the software: Sometimes updating the Engine Control Module (ECM) software can resolve the P0502 problem if it is software related.
  6. Professional diagnostics: If you are unsure of your skills or cannot fix the problem yourself, it is recommended that you contact a professional auto mechanic for more detailed diagnosis and repair.

It is important to resolve the cause of the P0502 code as it can cause the vehicle to not operate properly and create dangerous situations on the road.

Causes and Fixes P0502 Code: Vehicle Speed Sensor A Circuit Low Input

P0502 – Brand-specific information

Trouble code P0502 refers to a low vehicle speed sensor signal and can occur on various makes of cars, here are some examples of car brands with a P0502 code:

These are just a few examples, and the meaning of the P0502 code may vary slightly depending on the specific model and year of the vehicle. Please refer to the manufacturer's documentation or service manual for your specific vehicle make and model for accurate information.

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