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The exhaust gas recirculation (EGR) system helps minimize nitrogen oxide gases coming from your vehicle’s exhaust. This is important because nitrogen oxide gases are very harmful for the environment in significant amounts.

What happens when your vehicle’s powertrain control module (PCM) detects a fault in your EGR system? There are several OBD-II codes related to a faulty component in the EGR that may appear on your OBD scanner. One of them is the P0403 code.

car egr valve
The code P0403 activates when the PCM detects that the desired and actual states of the EGR control circuit do not match during operation.

What Does the P0403 Code Mean?

Diagnostic trouble code (DTC) P0403 stands for “Exhaust Gas Recirculation “A” Control Circuit.” It activates when the PCM detects that the desired and actual states of the EGR control circuit do not match during operation.

Nitrogen oxide gases usually form during the combustion process, and their levels spike when the combustion temperature increases. This is where the EGR system comes in.

The EGR system reduces the combustion temperature by taking a portion of the exhaust gases back to the intake manifold, making the air-fuel charge less combustible. It does this with the help of a component called an EGR valve that opens and closes, allowing air to flow back into the intake manifold.

On modern vehicles, the PCM controls the EGR valve. The module does so by operating one or more solenoids that open and close the valve. Depending on the vehicle design, the solenoid(s) may either act on the EGR valve directly or apply engine vacuum to the valve. Each of these control circuits are monitored by the PCM.

When the PCM detects improper voltage readings, it logs the P0403 code.

Note: The definition of code P0403 may be different depending on the vehicle manufacturer. Consult the appropriate repair manual or repair database for the exact code definition.

Vehicles that are prone to code P0403 include various models of Ford (especially Ford Crown Victoria), Dodge, Audi, Chrysler, and Mitsubishi.

What are the Possible Causes of the P0403 Code?

Since OBD-II code P0403 is a generic code, it is supported by various makes and models. However, the diagnostics and repair procedures for it may vary depending on your vehicle’s year, make, and model. Here are the common triggers of the P0403 code:

  • Faulty EGR valve
  • Faulty EGR vacuum solenoid
  • Carbon build-up in the EGR passages
  • Lack of proper vacuum to the EGR valve
  • EGR control circuit issues, such as damaged wires or poor connections
  • An issue with the PCM
car engine misfire
Engine misfire, stalling, and spark knock are some of the common symptoms of code P0403.

What are the Common Symptoms of the P0403 Code?

The error code P0403 usually has no other noticeable symptoms except:

  • Illuminated check engine light
  • Instability when idle
  • Engine misfires
  • Acceleration problems
  • Stalling
  • Spark knock
  • In some extreme cases, the vehicle may not start

For some vehicles, the P0403 code may not exhibit any noticeable warning signs.

How to Diagnose the P0403 Code

As mentioned, diagnostic and repair steps for the P0403 code may vary depending on your car’s year, make, and model. For example, repair steps for P0403 in Ford may differ from the repair steps for a P0403 code in a Chevy.

If you plan to fix the code yourself, you can watch the video below to help you get an idea of what diagnosis might involve. However, if you lack the DIY skill and experience, it is best to leave the job to professionals.

How to Fix the P0403 Code

Due to the various issues that can trigger the P0403 code, it can be tricky to resolve it. Leave the task to your mechanic if you are not confident with your automotive knowledge.

However, if you’re determined to resolve P0403 yourself, you can use online auto repair resources and guides to figure out the right way to clear the code. Check your owner’s manual to make sure the solution you found is appropriate for your vehicle.

Want to supplement your task with in-depth and up-to-date factory repair information? Consider securing an ALLDATA single-vehicle subscription. It will help you fix not only the P0403 code but also any other future issue your vehicle may encounter.

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Any information provided on this Website is for informational purposes only and is not intended to replace consultation with a professional mechanic.

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