How to Fix Code P0502: What It Means and How to Solve It

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speed sensor

As we all know, a flashing check engine light is an issue that all car owners must deal with every once in a while. When the code P0502 appears on your OBD scanner, you should not ignore it or disregard it. However, many people ignore this error code and continue to drive their vehicles, especially if they are unfamiliar with fixing it.

So, if you are like those, people worry no more as we will examine how to solve the P0502 error code as quickly and accurately as possible. We will also look closely at its causes and symptoms so the next time you experience this code error, you can diagnose it independently. 

What is Code P0502?

P0502 is a generic trouble code that indicates a faulty vehicle speed reading. The Power Control Module (PCM) monitors the vehicle's speed data using the speed sensors. As the speed sensors collect data, it compares the results to the data collected by the antilock brake control module or Electronic Brake Control Module (EBCM). 

When the PCM detects a difference in speed readings from the vehicle speed sensor and the wheel speed sensor, the code P0502 is triggered.

Symptoms of Code P0502

The Check Engine Light (CEL) and the oil pressure lamp are the most visible symptoms of code P0502. However, there are some signs you should be looking out for, and these includes:

  • Speedometer and odometer readings are erroneous.
  • When driving at constant speeds, the vehicle pulls to one side.
  • Strange noises originate from the engine compartment while driving, especially if additional symptoms           accompany them.
  • Other warning lights may illuminate, signaling a more serious issue such as an overheated service engine        or even a fire.

Causes of Code P0502

Although this code error is not as severe as we think, you should still need to determine what this code causes. This would help you address the issue accurately and avoid unnecessary repairs that could empty your pocket. So, what are the possible causes that can trigger this error code?

  • The speedometer in your vehicle is malfunctioning.
  • Your speed sensor is malfunctioning.
  • The issue is related to the wiring and switch.
  • A broken PCM 
  • A defective speed sensor

With all the causes mentioned above, this error code undoubtedly needs to be addressed as soon as possible to avoid more expensive repairs. You shouldn't think twice about bringing your car to a mechanic. 

You may also repair it yourself if you are knowledgeable about automobile repairs. If you are confident enough to fix the issue yourself, you may follow the steps below. 

How to Fix Code P0502?

A defective vehicle speed sensor is the most typical reason for the error code P0502; therefore, the repair will likely start there. If no further abnormalities are discovered, the mechanic will check the Engine Control Module (ECM), replacing parts if necessary.

Step-by-Step Guide

  1. Scan all the present trouble codes using an OBD scanner.
  2. Take note of any fault codes that are there and any freeze frame data that is available. If other                         transmission codes are present, take special note of their stored order if an intermittent failure is later           identified.
  3. Visually inspect all sensor signal wires and connectors with a magnifying glass. Look for anything that is         damaged, burned, shorted, or disconnected.
  4. You should visually inspect all wiring and connectors thoroughly. Damaged, burned, shorted,                             disconnected, and corroded wiring and electrical connectors should be identified. Make any necessary           repairs or replacements.
  5. If the problem persists despite visible damage to the wiring, prepare to test all associated wiring for                resistance, continuity, ground, and reference voltage.
  6. Pay special attention to this circuit if the sensor requires a 5-volt reference voltage (see the manual for            details). Check the resistance and continuity of this wire.
  7. If the reference voltage is correct, compare all other obtained readings to the manual's values, and make      any necessary repairs or wiring replacements if variations from the specified values are discovered.
  8. If all electrical values are correct, drive the vehicle normally while hooked up the scanner. If the code no          longer sets, there may be a problem in another part of the system, causing it.

If all the steps above didn't fix the issue, don't lose hope, as there are more ways to resolve the code P0502. Here are other possible fixes you can try:

  • Ensure that the vehicle's wheels and tires are the proper sizes.
  • It's better to upgrade a wheel speed sensor or sensors.
  • Replacing a hub bearing.
  • The circuit's wiring and connectors that detect vehicle speed must be repaired or replaced.
  • Installing a new speed sensor.

Common Mistakes When Diagnosing the P0502 Code

Mistakes when diagnosing are part of the repair process, especially when you are unfamiliar with the problem. However, not properly determining the cause may lead to expensive repairs, or worst, it could damage the rest of your car’s engine. So, what are the common mistakes people make in diagnosing the code P0502?

  • Replacing the speed sensor without verifying the actual cause.
  • Not checking the wiring and switch.
  • Replacing the PCM when the real problem is the speed sensor

P0502 Code FAQs

1. How serious is the code P0502?

This code error, as previously stated, is not as severe as others. To avoid the problem worsening, you should not leave it unattended for an extended period. Furthermore, leaving the Check Engine Light illuminated will result in an emission test failure.

2. How much is the cost of diagnosing the P0502?

The code P0502 can happen for various reasons, and a mechanic will need to determine the exact cause of the code. For $114.99, qualified mobile mechanics can come to your home or workplace to diagnose why you are getting this trouble code.

3. Can I drive when the check engine light is on?

Yes, you can continue driving, especially in an emergency. However, this still needs to be attended to as soon as you can. Scan your vehicle with an OBD scanner to see what codes appear so you can either fix it yourself or have a mechanic do it.

4. Is there special equipment I can use to pinpoint the cause of the code?

An OBD scanner tool will help you diagnose your vehicle without bringing it to a mechanic. Simply connect it to the car's computer system and interpret the trouble code readout.

5. Is it necessary to diagnose the cause of the code before repairing it?

Yes, diagnosing the possible causes is the first thing you need to do. Failure to perform it could harm your car components or, worst, your engine. It will also lead to costly expenses if not appropriately diagnosed.


Code P0502 is one of the most common error codes that result in the illumination of your Check Engine Light, but don’t worry - it’s not as serious as it sounds. There are many ways to fix this issue and, with the help of this guide, you can do it yourself. If you are not as savvy with cars, please don’t hesitate to contact your mechanic to ensure any problem gets resolved. 

We hope this guide helps you repair your car; if so, let us know what you think in the comments below!