Diagnostic Trouble Code P0402

P0402 “Exhaust Gas Recirculation Flow Excessive Detected”


What is code P0402?

Code P0402 stands for “Exhaust Gas Recirculation Flow Excessive Detected”. This diagnostic trouble code can show up for reasons related to the exhaust gas recirculation, or “EGR” system on your vehicle. Therefore, it is important to have a qualified technician diagnose the specific problem that caused the code to be stored in your vehicle’s computer.

Get this checked out soon by a CarAdvise shop, where the work will be guaranteed, and one of our expert techs will review any repair orders.

What does code P0402 mean?

The presence of code P0402 on a diagnostic scan of your vehicle indicates to a technician that there is something wrong with the exhaust gas recirculation (EGR) system. 

The EGR system helps your engine to run efficiently, consume less fuel, and emit fewer emissions. It accomplishes this by recycling a small amount of exhaust gas back to the intake system. There, the exhaust gas mixes with the air that enters the combustion chambers. As a result, the chemical composition of the intake air is changed; the amount of oxygen decreases, lowering combustion temperatures so that less of the hazardous nitrogen oxide gas is produced as a byproduct. This allows for a cleaner and more efficient exhaust system. EGR systems are controlled either electronically or by vacuum, depending on your vehicle make, model, and age.

If the EGR system is sending too much exhaust gas to the intake, your vehicle’s ECM (Engine Control Module) will detect the problem, store code P0402, and turn on the check engine light.


What causes code P0402?

A number of causes can trigger a code P0402. That is why an accurate diagnosis is essential. Causes of this code include:

Most likely

  • Defective EGR valve ($200-$500)
  • Excessive vacuum or electrical input to the EGR valve

Other possibilities


What symptoms are associated with this code?

Common signs associated with a code P0402 include the following:

  • The check engine light is on or flashing
  • Reduced fuel economy
  • Rough idle, hesitation, or engine stalling
  • Engine misfire or lack of power


How does a technician diagnose code P0402?

If a diagnostic scan of your vehicle indicates a code P0402, a technician will perform tests to pinpoint the problem. These tests include checking for any related trouble codes. The technician will also visually inspect the EGR system and look for any loose or cracked vacuum lines in the engine compartment. A multimeter might be used to run tests on the EGR valve, and the technician might manually actuate the valve while the engine is running to see if there are any changes to engine speed. If necessary, the technician might need to remove the EGR valve and other related components to clean or inspect. The catalytic converter might also need to be inspected for signs of blockage.


How serious is this code?

In many cases, a code P0402 will not cause any major drivability problems. But in some cases, the problem can lead to a rough engine idle, hesitation, or stalling when you try to accelerate. At the very least, the presence of the check engine light will prevent your vehicle from passing an emissions test. And if the catalytic converter is causing the problem, your engine could lack power or even fail to start.

Get this checked out soon by a CarAdvise shop, where the work will be guaranteed, and one of our expert techs will review any repair orders.


Related Diagnostic Trouble Codes

P0400 Exhaust Gas Recirculation Flow Malfunction

P0401 Exhaust Gas Recirculation Flow Insufficient Detected

P0403 Exhaust Gas Recirculation Control Circuit


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