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Code P0406. Exhaust Gas Recirculation Sensor A Circuit High

In simple terms, the code P0406 It’s a sign that your car’s engine needs to be checked immediately. This code is defined on your scanner as “Exhaust Gas Recirculation Sensor A Circuit High”.

If you ignore this EGR system code, there is a good chance that your car’s engine will fail very soon. You won’t be able to drive your vehicle properly, and even worse, you’ll end up paying for expensive engine repairs.

So as soon as you notice that the diagnostic code P0406 is activated in your scanner, take your vehicle to be diagnosed, either by yourself or in a specialized workshop.

What is the EGR System?

EGR stands for “Exhaust Gas Recirculation”, which means “Exhaust Gas Recirculation”. This system is responsible for taking part of the exhaust gases and sending them back to the engine for combustion.

This recirculation of gases allows the car to emit fewer polluting gases, especially nitrogen oxide, which is burned in this “second combustion”.

The EGR System is controlled by the PCM module, through the EGR valve. This valve can open and close depending on the requirements of the PCM, which in turn makes these decisions based on signals from oxygen sensors 1 and 2, and the EVP sensor.

The EGR valve may have one of the following control methods:

  • Electronic EGR valves, whose drive is purely electronic, are controlled directly by the PCM.
  • Vacuum EGR valve, in which the valve is activated by an intake vacuum line, which controls the PCM.

The EVP sensor transmits signals to the PCM indicating the actual position of the EGR valve. These signals are voltage signals and will depend on how open the valve is or not.

But if the PCM receives a very high voltage, outside of specifications, it activates the P0406 code and the indicator signal “Check Engine” on your dashboard. When this occurs, it may be because the valve is stuck in one position, the EVP sensor is damaged, or there are wiring problems that do not allow an adequate signal to be received.

What is Code P0406?

P0406 is a generic ODB2 trouble code that would indicate that there is a voltage value above the default in the exhaust gas recirculation EGR circuit signal.

Error code P0406 can be identified as Exhaust gas recirculation sensor “A” circuit high. When the ECM detects that the EGR valve voltage is higher than the allowable range, the check engine light will flash on your dashboard.

As we already mentioned, this signal comes from the EVP sensor, which is responsible for monitoring the position of the EGR valve and sending a voltage signal to the PCM.

This fault code usually does not affect the driving of the car, since its symptoms are very mild. The driver will only notice the Check Engine light activated, but the car will continue to operate normally.

However, it does not mean that you can “forget” this code and continue driving without taking action. If this system does not work correctly, you will see an increase in your usual fuel consumption, plus your car will be more polluting.

In some cases, this failure can even affect engine performance. You will notice that the engine is less powerful.

You may also be interested in Code P0403. Causes, Symptoms, Diagnosis and Repair

Symptoms of Code P0406

A code P0406 You may have one or more of the following symptoms:

  • The check engine light comes on. Any problem with the car’s engine will activate the “Check Engine” light.
  • Reduced engine performance. In some cases, the EGR valve problem affects the performance of the engine, and therefore, the car.
  • High harmful emissions. Instead of clean, safe emissions, your car emits more harmful gases than permitted by law. You will not pass the emissions tests at the MOT.
  • The engine stops more frequently. In severe cases, the engine’s performance is so compromised that it even tends to shut down for no apparent reason.
  • Poor fuel economy. You begin to refuel more frequently, indicating a variation in fuel consumption.

Keep in mind that in most cases, drivers do not notice any of these symptoms except for the check engine light signal. If the symptoms are mild, you can continue driving the car until you reach your trusted workshop.

But beware! Don’t let too much time go by without repairing this. Driving the car in these conditions can aggravate the symptoms over time and affect other components of the car.

Possible Causes of Code P0406

P0406 is an engine trouble code that could mean problems with the EVP sensor, EGR valve, or control wiring. The most common is a bad EVP sensor, but you shouldn’t rule out any of the other causes until you make a diagnosis.

In this case, the valve can be replaced and the problem is solved quickly. But this does not mean that you should rule out other causes. Let’s see a list of common causes:

  • Leak in the vacuum line to the EGR valve.
  • EVP sensor signal circuit problem.
  • Damaged EVP sensor.
  • Defects in the EGR valve.
  • Bad electrical connection.
  • EGR valve clogged by dirt and carbon.
  • The wire harness may be open or shorted.

As you can see, the causes are related to the EGR valve, the EVP sensor, and the wiring harness, including the power and control circuits. Therefore, it will be easy to diagnose the fault.

How to Diagnose Code P0406

Here we show you the steps you must follow to diagnose this fault code:

  1. Scan your car with an OBD2 device. Verify that code P0406 is activated, and if any other code exists.
  2. Then erase all these codes and start your car to take a test drive for about 15 minutes. This to check if the code returns.
  3. If the code returns, you should proceed to a visual inspection of the EGR system.
  4. Perform a visual inspection for damaged or frayed cables, broken vacuum lines, and loose electrical connectors.
  5. Proceed to repair if problems with wiring, connections, and vacuum lines are detected.
  6. Check the EVP sensor, check for damage, and check its continuity and voltage.
  7. You must replace it if it is damaged.
  8. Next, check the EGR valve and make sure it is not stuck. Disassemble it and clean it of dirt and carbon. The valve must be free to move, without jams.
  9. Reassemble the EGR valve.
  10. If the valve does not activate, you should replace it, although this is not common.
  11. If at this point the code still is not clear, you should take the car for a deep diagnosis that includes the PCM module. Module failure is not common, but it can happen.
  12. In these cases, the PCM is reconfigured or changed.

In most cases, repairing the electrical circuit or changing the sensor is enough to clear the code and resolve the problem. These repairs are not expensive.

How to Fix Code P0406

Do not take any repair or replacement action without first performing the diagnosis. Proceed according to the diagnostic results and repair what is detected.

Repairing this fault is simple, and usually inexpensive. Among the corrections that can be made in this system to resolve the P0406 code, we have:

  • Repair damaged connections.
  • Wiring repair or replacement.
  • EGR valve vacuum line repair.
  • Replacing the vacuum line.
  • Cleaning the EGR valve due to clogging.
  • Replacing the EGR valve.
  • Replacing the EVP sensor.

Common Errors When Diagnosing Code P0406

The most common error when trying to solve this failure is changing the EVP sensor without carrying out the proper diagnosis. For example, if the valve is stuck, this code will also be triggered, and changing the sensor will not solve the problem.

It is very important to carry out a proper step-by-step diagnosis of the P0406 fault code and at the same time perform all the steps carefully.

So make sure you don’t overlook the real problem and make repairs accordingly.

Can You Drive With Code P0406?

In most cases, the code P0406 It’s no big deal, and some drivers may still drive with their vehicles displaying the error code. It does not affect driving and its symptoms are almost imperceptible.

The code does not affect the driving of the car unless your symptoms are very intense. What you should be worried about is that this code does not allow you to pass the emissions test on ITV.

Additionally, symptoms can worsen over time and affect other components of your engine. It is recommended that you carry out the repair as soon as possible.

Never ignore P0406 codes and problems. If you are not so savvy about cars and technology, it would be better and safer to take your vehicle to a qualified technician for an immediate diagnosis.

How to Avoid Code P0406?

This code can be avoided by performing preventive maintenance recommended by the car manufacturer and doing routine checks of all control systems.

For example, traffic jams in EGR valves can occur due to excess carbon, which is perfectly avoidable by keeping the fuel system, intake, and ignition systems up to date.

If combustion is ideal, you will see very little carbon in this area of ​​your car that could clog the EGR valve.

It should be noted that not all failures in your car can be avoided. There are some that occur as part of the life cycle completed by the component. An example of this is the EVP sensor.

This sensor can fail and activate the P0406 code for no special reason, except for its lifespan to expire. And it’s not a sensor worth putting in a predictive plan. It is only changed when it is damaged.

Is Code P0406 Serious?

By having such minimal symptoms, and not affecting the driving of the car, this code is mild in severity.. You can continue driving the car without affecting other components, for a reasonable time. We recommend that you do not extend this time and correct it as soon as possible.

The severity of the code is given by something else: The emission of gases. As we already mentioned, a car in these conditions will not be able to pass the emissions tests in the technical inspection.


You may also be interested in Error Code P0402 – Excessive exhaust gas recirculation flow detected

The P0406 code It is one of the mildest fault codes that your car can suffer from. But this does not mean that you can forget about the fault and not repair it.

Diagnose and repair it on time, and if you consider that you cannot do it yourself, take it to your trusted workshop.

If you want to know other articles similar to Code P0406. For exhaust Gas Recirculation Sensor A Circuit High you can visit the category Fault Codes.


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