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Code P0406: Exhaust Gas Recirculation Sensor A Circuit High

If you want to save some money by not taking your vehicle to the mechanic, there is a system that can help you repair it yourself. Most modern vehicles have an error code system, which tells you exactly what is wrong with your vehicle. If, for instance, you receive an OBD-II scanner error code P0406 problem, that means there is a problem with the exhaust gas recirculation system. If you hope to do the repairs yourself, you need to know how the exhaust gas recirculation system works, what might be wrong with it, and what needs to be done to repair it. Our guide has everything you need to know.

What Does the Error Mean?

The first question you need to ask is, “What does the code P0406 mean?” The exhaust gas recirculation system is a system in your vehicle that lowers the combustion temperature by reusing some of the exhaust. A portion of the exhaust is redirected back to the engine and injected into the cylinder along with the fuel and air mixture. This allows the mixture to combust at a lower temperature, which in turn, allows the vehicle to run more efficiently.

Inside the exhaust gas recirculation system is a valve controlled by the powertrain control module, or PCM. This valve is either vacuum controlled or electronically controlled and has a sensor that detects what position the valve is in. If this sensor detects that the valve is not opening and closing properly, it will send the P0406 error code. Essentially, this means that the exhaust gas recirculation system is not functioning correctly, which may cause several symptoms that impair your ability to operate your vehicle.

Understanding the Symptoms

There are not too many symptoms caused by the P0406 error code that drivers will notice. Several of them are quite subtle, or entirely undetectable without special tools. The first symptom will likely be the check engine light turning on. Then, you may also experience:

  • The engine stalling
  • The engine surging
  • Increase in NOx emissions
  • Increase in engine temperature

As you probably know, the engine stalling or surging can be dangerous. If it happens at the wrong time, it can cause an accident or cause you to hit a pedestrian. You should never ignore the P0406 error code, especially if you have started to notice these symptoms. Additionally, this issue will prevent you from passing your smog test, which will make it illegal to continue operating your vehicle. Finally, it is possible that the cause of this issue may cause other issues as well.

What Can You Do About It?

The big question is, “How do I fix trouble code P0406?” It is always a good idea to start with the simplest solution and work toward the more difficult ones. This error code may be caused by a faulty sensor and there is nothing wrong with your recirculation system at all. This is very likely if you experience no unusual symptoms at all. Find the sensor and inspect it and the surrounding connectors for damage. If you find any frayed wires or other damage, repair or replace the components. You can use electrical tools to test the function of the sensor without the engine running.

If there is nothing wrong with the electronics, then you should next find the recirculation valve. Debris may be stuck in it, which is preventing it from opening and closing. If this is not the case, the valve itself may be damaged. If your valve is vacuum operated, there may be a crack in the vacuum line. If you cannot find anything mechanically wrong with the recirculation system, it is time to evaluate the state of your PCM.

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