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P0403 Code – What Does It Mean & How To Fix It

This is one of the most frequent OBD2 trouble codes. Read the full article below to know what it means, how to fix it, and what other codes may show related to it.

Definition

A P0403 Code defines a malfunction with the Exhaust Gas Recirculation Circuit.

Meaning

The P0403 Code indicates that the Engine Control Module is detecting a series of malfunctions concerning the engine Exhaust Gas Recirculation circuit. The Engine Control Module is sensing a short or open circuit in the EGR’s vacuum control solenoid is occurring.

This means that your vehicle’s Engine Control Module (ECM) is getting an electrical signal that there is a problem within the system. 

The EGR system helps to control the emissions coming from your vehicle based on the temperature coming from the engine. If the engine is detected as running too hot, the ECM will trip a “Check Engine Light” error. 

The EGR is designed to lower the temperature of the fuel combustion, which prevents harmful chemicals from leaving through the exhaust section. 

Causes

  • Possible EGR vacuum line leak
  • A short in the EGR solenoid
  • Water going past or resting on the solenoid
  • Power Control Module (PCM) could be shorting out
  • Loose connectors at the EGR solenoid
  • The EGR valve might have failed

Symptoms

Some vehicles might not notice much more than the “check engine” light is on with this type of problem. 

Others might experience the following problems:

  • Engine stalls
  • Engine misfires when first started but goes away after the engine warms up
  • Heavy smell of fuel coming out of the exhaust
  • The Engine Control Module may disable the Exhaust Gas Recirculation (EGR) System

Diagnosis

It’s recommended to check this error out by scanning with an OBD-II tool. It will plug into the vehicle OBD-II port and sends you the proper error code. If you don’t have one, just locate your nearest local auto repair center. The technician there will use their scanner to send certain tests through the port to diagnose your vehicle’s OBD-II code.

Most of the time the technician will reset the code that’s making the check engine light come on. A test drive of the vehicle is normal to see if the check engine light will come on once again. If it does and the scanner confirms the same error code, then the technician will know which areas to check first. 

The first thing the technician will/should look at is the wiring and connections going to the EGR temperature sensor and the EGR solenoid. Loose connections are a common problem when troubleshooting P0403 Code problems. 

Next, the EGR valve vacuum control solenoid should be checked by unplugging it to check for a short circuit. 

Another common procedure that the technician will most likely perform is the testing of the EGR valve. The tool that will be used is called a Dynamometer. It will test whether or not the Nitrogen Oxygen (NOx) levels are going down when the EGR valve is opened. 

If the NOx levels are in fact going down, that would normally mean that something within the EGR passages or cylinders are being restricted or even blocked by some sort of debris or materials. Backfiring will commonly happen if there is a blockage with the EGR passages. 

Common mistakes

Before you start replacing parts like solenoids and sensors, check for these things that might be overlooked. 

  • Always check the wiring for any type of cuts, rubbing and most especially exposed wiring that could short out the EGR sensor
  • Don’t forget to check for liquids or corrosion on any of the connectors or the ports.

How serious is this?

The Engine Control Module (ECM) will actually disable the EGR if shorts are detected. This means your Exhaust Gas Recirculation System will not work properly, possibly causing more than normal dangerous fumes to come from your vehicle. 

If the Exhaust Gas Recirculation System stops working, you’ll probably have difficulty passing any type of emissions test. 

What repairs can fix the code?

If you find any sort of damaged wiring, please get that part replaced or repaired first. Faulty wiring is one of the most common issues associated with OBD-II error codes and your check engine light activating.

Corrosion of the connection points is also another common issue with the EGR solenoid and sensor. 

Finally, replacement of the EGR solenoid should be performed after exhausting all other options. 

Related codes

P0401 - EGR experiencing insufficient flow

P0402 - EGR experiencing excessive flow

P0404 - EGR has performance issues

P0405 - EGR Valve Position Sensor has a low voltage problem

Conclusion

As you should be able to tell by now, a P0403 Code can be caused by many things. It’s something that’ll definitely need to be checked out because it can get worse down the road. 

The EGR needs to work properly in order to regulate the temperature of gas combustion. This helps to prevent unusually harmful emissions from coming out of your exhaust. 

If your Engine Control Module (ECM) disables the EGR because of a sensor signal, try to get your to an auto repair shop as soon as possible.