OBD-II Trouble Codes

P0402: Exhaust Gas Recirculation “A” Flow Excessive Detected

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The EGR or exhaust gas recirculation system helps moderate a vehicle’s nitrogen oxide emissions by lowering combustion temperatures. Just like any other car part or any other system in your engine, there may be faults that prevent your EGR from working properly. One of the OBD II trouble codes related to EGR is code P0402.

What Does the P0402 Code Mean?

Diagnostic Trouble Code (DTC) P0402 stands for Exhaust Gas Recirculation “A” Flow Excessive Detected. It indicates that the powertrain control module (PCM) has detected excessive EGR.

It is one of the generic diagnostic trouble codes in a number of makes and models that are related to the vehicle’s EGR.

EGR valve of a car
Code P0402 indicates that your car computer has detected excessive EGR.

Note: The definition of code P0402 may be different depending on the vehicle manufacturer. Consult the appropriate repair manual or repair database for the exact code definition.

EGR System

The EGR system controls the amount of nitrogen oxide emissions by lowering engine combustion temperatures. Nitrogen oxide gases are formed when the temperature in your combustion chamber is too high. How does the EGR system help in reducing these NOx gases?

There are different EGR system designs in use today. Although the specifics of each system may vary, all use some type of EGR valve. When conditions are correct, the PCM commands the EGR valve to open, allowing exhaust gases to be recirculated into the engine’s intake manifold. Introducing these inert gases into the engine lowers combustion temperatures and reduces NOx emissions.

EGR is only needed in limited amounts under certain driving conditions. If the PCM detects that there is excessive EGR flow, it may turn on the check engine light and trigger code P0402.

It’s important to note that code P0402 is often set in Ford vehicles that use a differential pressure feedback EGR (DPFE) sensor to determine how much EGR is flowing.

What are the Possible Causes of the P0402 Code?

Here are possible triggers of the P0421 code:

illuminated check engine light
The check engine light can turn on for many issues, including code P0402.

What are the Possible Symptoms of the P0402 Code?

Generally, faults related to this code will cause drivability problems. However, symptoms may differ depending on the vehicle you own. Here are some of the common symptoms related to code P0402:

How to Diagnose the P0402 Code

P0402 is a generic code, and it can be seen in many makes and models. However, keep in mind that diagnostics and repair procedures may be different per car manufacturer or depending on your vehicle’s year, make, and model. For example, procedures to fix a P0402 code in Ford may differ from the troubleshooting process of a P0402 code in Toyota. Here are video clips to give you an idea of what the troubleshooting process might involve:

How to Fix the P0402 Code

The first step to resolving the P0402 code is diagnosis. Once you’ve established what triggered the code, start researching the appropriate fix. Use online auto repair resources. Be sure to look for a solution that’s specific to your vehicle’s year, make, and model.

If you’re not confident with your automotive know-how and DIY repair skills, let your mechanic address the P0402 code.

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