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Code P0403. Causes, Symptoms, Diagnosis and Repair

Are you experiencing “check engine” lights with the code P0403 activated? Don’t be scared, it could be much simpler than you think. If you have no idea what it means, look no further, you are in the right place.

We are going to introduce you to everything you need to know about the P0403 fault code. Code P0403 It is accompanied by the following description: Malfunction of the exhaust gas recirculation (EGR) control circuit “A”.

Operation of the EGR Gas Recirculation System

The exhaust gas recirculation system is an integral part of the vehicle’s exhaust system. Its function is to prevent the formation of NOx (nitrogen oxides) in the cylinders.

The EGR is controlled by the car’s computer, which opens or closes the exhaust gas recirculation system depending on load, speed, and temperature, to maintain the proper cylinder head temperature.

There are two cables that control and communicate with the computer. There are a total of 5 wires to the solenoid. Another 2 are battery voltage and ground. As well as a reference terminal for 5 volts, generally located in the center.

If the engine computer does not see any voltage change when it tries to open or close the EGR, it is perceived as an error. A fault code P0403 is then written to memory.

Unleaded fuel is prone to the formation of NOx (nitrous oxide) at extreme temperatures in the engine. The exhaust gas recirculation system sends a controlled amount of exhaust gases to the intake manifold.

This is done to sufficiently dilute the incoming fuel mixture. This is to reduce the cylinder head temperature below the temperature at which NOx is generated.

The correct operation of the exhaust gas recirculation system is not only necessary to avoid NOx emissions. It also gives the engine more power without detonation and a leaner fuel mixture for better fuel economy.

You may also be interested in Code P0401. Causes, Symptoms, and How to Diagnose It

What is Code P0403?

This code P0403 refers to a malfunction of the exhaust gas recirculation (EGR) system. To be more precise, it refers to its electrical part.

This code is a general on-board diagnostic (OBD) code for vehicles. Indicates that the EGR circuit has failed or has stopped working. This code belongs to a large list of generic diagnostic codes.

OBD codes are called generic because they apply to all makes and models of cars after 1996. This means that these codes indicate the same problem and are usually fixed in the same way.

However, in rare cases, there may be some differences between the various models in terms of how to fix it.

Relationship Between EGR And Code P0403

When the engine is running, fuel is burned through an ideal oxidation reaction. This reaction is like this:

Oxygen from the air (O2) reacts with organic fuel (simplified as CH) to produce carbon dioxide gas (CO2) and water (H2O).

These gases are expelled through the vehicle’s exhaust. Unfortunately, engine overheating makes this reaction difficult to achieve ideally. This leads to incomplete burning of the fuel.

Additionally, factors such as temperature, air pressure, and humidity change affect the final result of the reaction.

These changes affect this combustion reaction and make it difficult to achieve. As a result, nitrogen gas (N2) is oxidized into different nitrogen oxides. These oxides pollute the environment, causing acid rain and respiratory problems.

The EGR’s job is to prevent this from happening. It works by lowering the combustion temperature of the fuel.

It also reintroduces unburned fuel into the engine for complete combustion. They achieve this by recirculating non-reactive exhaust gases into the cylinders.

These gases are responsible for lowering the reaction temperature while burning at a much slower rate. This way, only oxygen is burned with the car’s fuel.

The EGR It has a valve that redirects these exhaust gases to the cylinders. This valve is controlled by a power control module (PCM). If the EGR operates by applying vacuum, the PCM is responsible for applying that vacuum by opening the EGR solenoid.

If the EGR solenoids do not respond to the PCM, the P0403 code is read and the “Check Engine” light displays on the dash.

Symptoms of Code P0403

The main sign that a P0403 error has occurred is the Malfunction Indicator Lamp (MIL), also known as the Check Engine.

Typically, you probably won’t notice any symptoms unless the “Check Engine” light comes on. However, in some cases, one or more of the following signs can be detected:

  1. The engine stops or starts poorly.
  2. Attempts to stall at idle.
  3. The vehicle’s engine may become unstable.
  4. Higher fuel consumption.
  5. Decrease in engine power.
  6. Sometimes there may be no symptoms, despite the stored fault code.
  7. A rough start of the engine or misfires that disappear when the engine warms up
  8. There is a smell of gasoline coming out of the exhaust.

Causes of code P0403

Error code P0403 It may mean that one or more of the following problems have occurred:

  • Short circuit to ground in the EGR system control circuit.
  • Wiring problem or damaged connector.
  • Corrosion of cables or electrical connections.
  • Clogged exhaust gas recirculation valve passages.
  • The exhaust gas recirculation system vent is clogged.
  • The exhaust differential pressure sensor passages may be clogged.
  • Damaged vacuum lines or hoses.
  • Defective exhaust gas recirculation valve position sensor.
  • Excessive accumulation of soot, which prevents the free movement of the EGR valve.
  • Defective EGR.
  • In rare cases, malfunctions of the engine control module (ECM).

How to Diagnose Code P0403

Some suggested steps to troubleshoot and fix error code P0403:

  1. Connect an OBD-II scanner to the vehicle’s diagnostic connector and read all stored data and error codes.
  2. Clear the error codes from the computer’s memory and test drive the vehicle to see if the P0403 code appears again.
  3. If the error code appears again, visually inspect the electrical cables and connectors related to the exhaust gas recirculation system.
  4. If necessary, repair or replace any shorted, broken, damaged or corroded components.
  5. If the problem persists, check the exhaust gas recirculation system passages to see if they are blocked.
  6. Inspect the vacuum lines and thoroughly check for vacuum leaks.
  7. Check the operation of the exhaust gas recirculation valve and the ventilation control solenoid valve.
  8. Check the operation of the exhaust recirculation valve position sensor and the absolute intake manifold air pressure sensor.
  9. Measure the voltage of the system vent control solenoid valve circuit using a digital multimeter.
  10. Compare the value with the manufacturer’s datasheet, and replace the faulty valve if necessary.
  11. If the problem persists, check and replace the engine control module (ECM) if necessary.

Common Errors When Diagnosing Code P0403

A common mistake may be the fact that do not disconnect the connection to the EGR control solenoid to check the connection for a buildup of corrosion, which could cause an open circuit in the ECM.

Be sure to check the wiring harness for cut wires causing an open circuit before replacing a properly functioning solenoid.

To carry out the repair, you should always be guided by the results achieved in the diagnosis. Do not replace parts if you are not sure they really need to be changed.

How to Fix Code P0403

Allow your vehicle’s engine to cool. In most cases, exhaust gas recirculation (EGR) systems are very hot, as they are usually installed directly into the exhaust system. Therefore, if you don’t let the engine cool down, you can get burned.

Inspect all vacuum lines, they do not tolerate high temperatures well and this is not uncommon in a recirculating system. Any vacuum line that is burned or broken should be replaced or repaired.

Be sure to carefully check the integrity of the wire harnesses involved. They often run along and around the exhaust pipe. Therefore, it would be a good idea to tie up any loose cables.

If you find a burned wire, solder the connections and make sure they are properly insulated.

Inspect the vent solenoid for cracks and water intrusion. Also, make sure the connectors are properly connected electrically and that the latches are not damaged or broken.

If you have access, you can remove the exhaust recirculation valve to check its condition. These valves are susceptible to significant soot buildup.

Use a carburetor cleaner and a toothbrush to remove soot from dirty areas.

Is Code P0403 Serious?

Not really the code P0403 In general, it does not pose any risk to the user when driving. It also does not affect the performance of the car. Many times the driver will only notice the “Check Engine” light on his dashboard.

However, there are extreme cases in which other symptoms appear that affect engine performance. Even these symptoms can shut down the car for no apparent reason.

A rough idle, difficult starting and black smoke from the exhaust can indicate the severity of the problem. If this is your case, it is best not to let too much time pass without diagnosing the fault and repairing it.

How to Avoid Code P0403?

The EGR It is one of those systems that are difficult to access for the average user, so routine inspection is not feasible. However, checking the wiring from time to time can prevent major problems.

Checking the vacuum hoses and checking for leaks is also a good idea to keep this code out of your memory.


You may also be interested in Error Code P0405 (Symptoms, Causes and How to Fix It)

That being said, you now have a better understanding of the code P0403. As you can see, the range of symptoms in this code is wide. This means it can be as simple as turning on the “Check Engine” to a completely disabled engine.

This code should usually give you more than enough time to get to a place where you can safely verify it. However, the sooner you repair it, the better.

If you want to know other articles similar to Code P0403. Causes, Symptoms, Diagnosis, and Repair you can visit the category Fault Codes.


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