How to Fix Code P0503: A Guide to Solving Vehicle Speed Sensor Issues

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vehicle speed sensor

When your Check Engine Light illuminates, and you see the Code P0503 on your OBD scanner, your Vehicle Speed Sensor (VSS) is malfunctioning. This could cause many problems with your vehicle and even lead to engine failure if left unchecked. 

This article will explore the causes, symptoms, and potential fixes for code P0503. Read on!

What is Code P0503?

P0503 is an OBD-II generic code defined as "Vehicle Speed Sensor (VSS) -intermittent/erratic/high input." This trouble code is set when the car's computer detects a VSS signal indicating a value outside the expected range. 

When we say signals outside the intended range, it includes higher and lower than expected values. Also, those erratic, intermittent, or do not correlate with input data from one or more wheel speed sensors are considered unexpected values.

Symptoms of Code P0503

When you have this error code on your scan tool, there are a few symptoms that you may notice. These include:

  • Check Engine Light illuminated.
  • The speedometer may work erratically.
  • Not working ABS
  • Irregular gear shifting
  • Problem with activation/deactivation of the traction control system (if equipped)

Causes of Code P0503

When you begin to see and experience the symptoms listed above, you will likely wonder what is causing them. Numerous factors are associated with this error code, so make sure you diagnose all of them to find the precise cause. Some of the reasons could be:

  • Damaged wiring harness and connectors in the speed sensor
  • Broken or faulty speed sensor
  • Dirty build-up on speed sensors
  • Open or shorted wiring or electrical connectors in the vehicle speed sensor circuit
  • Defective ECM (Engine Control Module)
  • Improper ignition timing
  • Incorrect wheel size
  • Leaking fuel injectors
  • Faulty PCM

How to Diagnose Error Code P0503

Diagnosing the trouble code is one of the critical parts of fixing the issue. You won't know the exact problem without diagnosing the possible causes that triggered the code P0503. To do this:

  1. The first step is to inspect the system wiring, speed sensors, and connectors. Check if any of them is damaged or broken. If everything looks fine, move on to the next step.
  2. Using your OBD scanner, scan and retrieve all stored trouble codes and freeze frame data. Make sure to note all the information to help you identify the problem.
  3. After writing down all the information obtained from the scanning tool, clear all the fault codes and perform a test drive. Check whether the symptoms have gone away or reset the code.
  4. Check the wheels and tires and make sure that they are installed correctly.
  5. Locate the vehicle speed sensor and check the circuit connectors and wirings. Make sure they are not damaged.
  6. If you haven't found the root of the problem yet, it's time to test the vehicle speed sensor for faults.

Also, don't forget to inspect the following:

  • Wheel speed sensors
  • Tone rings
  • ECM for faults

How to Fix Code P0503?

After diagnosing each of the possible causes, you may probably find out the root of the problem. Now it's time to fix code P0503 with one of these methods:

  • Replacing the wheel speed sensor
  • Replacing a hub bearing
  • Cleaning the speed sensor
  • Replacing the ECM

Step-by-Step to Replacing the Wheel Speed Sensor

What you Need:

  • New wheel speed sensor
  • Socket set
  • Ratchet
  • Wrench set
  • Flashlight
  • Floor jack and jack stands


  1. Park the vehicle on a leveled surface and set the parking brake.
  2. Disconnect the negative battery cable.
  3. Loosen the lug nuts using the appropriate socket.
  4. Jack the car up and secure it on jack stands.
  5. Using a ratchet, remove the bolt that holds the sensor to the tone ring.
  6. Remove the sensor and disconnect the wiring harness.
  7. Install the new sensor and connect the wiring harness.
  8. Tighten the bolt that holds it in place with a wrench set.
  9. Reinstall the wheels.
  10. Jack the vehicle back down and tighten the lug nuts.
  11. Reconnect the negative battery cable.
  12. Start the engine and check for proper operation.

Step-by-Step Guide to Replacing a Hub Bearing 

Replacing a hub bearing assembly is a pretty straightforward process, but there are some things you'll want to take into consideration before getting started.

  1. First and foremost, always make sure your car is appropriately jacked up and supported using jack stands. It's also essential to remove the wheel that the assembly sits on so you have more room to work.
  2. Once the wheel is off, use a breaker bar to remove the hub assembly's bolt in place. Be sure to use caution and apply pressure evenly when doing this, as you don't want to damage the threads on the axle.
  3. Remove the old hub bearing assembly and replace it with the new one. Before installing it, be sure to apply a thin layer of grease to the races on the new assembly.
  4. Reattach the hub bolt, making sure it's tight, and replace the wheel. Lower your car and take it for a test drive to ensure everything is working correctly.

Step-by-Step Guide to Cleaning the Speed Sensor

As mentioned earlier, a dirty speed sensor is one of the common causes of the code P0503, so it's good to clean the sensor before replacing any components. Here's how to do it:

  1. Locate the speed sensor. It's usually located near the wheel or suspension system. It looks like a small metal canister with two wires coming out by cleaning the speed sensor.
  2. Open up the sensor. There should be screws on the top that allow you to open it up. Be careful not to lose any of the screws because they are tiny and hard to find once they fall off.
  3. Once the sensor is open, use a brush or compressed air to clean out dirt or debris. You may also want to use some contact cleaner on the connectors to help remove any corrosion.
  4. Reassemble the sensor and test it out. Once everything is back together, start up your car and see if the code goes away.

If you've followed these steps and the scanner is still throwing a code, it's time to replace your PCM. However, the good news is that this is a much less common occurrence and is most likely caused by a faulty sensor.

Common Mistakes When Diagnosing the Code P0503

As the code P0503 is one of the error codes associated with many causes and symptoms, it's easy to make a mistake when diagnosing it. Here are the common mistakes people make:

  • Assuming that a faulty ECM causes the code, the real reason is the incorrect wheels and tires.
  • Replacing the PCM immediately without diagnosing all the possible causes.
  • Not checking the wirings and connectors before replacing other components.
  • Not writing down the trouble codes and freeze frame data retrieve from the scan tool.

Code P0503 FAQs

1. Is the code P0503 serious?

The code P05003 is not a severe error and can be fixed with troubleshooting. However, if it's left untreated, it can cause more damage to the engine.

2. What does an erratic speed sensor mean?

An erratic speed sensor could mean that the sensor is not reading the correct information. This could be caused by several things, such as a bad connection, debris on the sensor, or even corrosion.

3. What is the role of the speed sensor?

The speed sensor is responsible for sending information to the ECU about how fast the car is moving. The ECU uses this information to control fuel injection and ignition timing.

4. Is it possible to test the speed sensor?

Yes, it is possible to test the speed sensor. One way to do this is with a diagnostic tool. Another way is to check the sensor's output with a voltmeter.

5. Do I need a special tool to diagnose this error code?

You do not need a unique tool to diagnose this error code. However, a diagnostic tool will make the process much easier.


So, what do you do if your car has the dreaded P0504 error code? This trouble code may seem complicated to diagnose because of the many causes and symptoms. But once you know what is causing it, the fixing part is not too difficult. 

We hope this article has given you the information you need on what code P0503 means and how to fix it. If it may be too hard for you, please contact a professional mechanic to help you out. Thanks for reading!