Nissan Patrol P0400: Meaning, causes and diagnosis


P0400 Nissan Patrol

P0400 is a standard code that indicates that your Nissan Patrol’s EGR system is not working. The good news is that this code does not pose a risk of breakdown and should not affect the operation of your Patrol (assuming it is the ONLY code).

P0400 is a generic code, meaning it has the same definition for the Patrol as it does for any other vehicle.

The most common cause is a faulty EGR valve, wiring, or vacuum line.

P0400 Definition

Meaning of P0400: Nissan Patrol

Here is the definition of P0400 broken down into two parts. Understanding why you have the code is essential to diagnosing and fixing it.


The exhaust gas recirculation system (commonly called the EGR system) allows exhaust gases to enter the combustion chamber a second time. The EGR system does not provide any benefit to engine performance; It is done purely to meet emissions standards.

In fact, it’s one of the oldest forms of emissions technology in existence, meaning there’s been plenty of time to perfect it.

Flow failure

Exhaust gases do not enter the combustion chamber, indicating that the EGR valve or solenoid is not working properly. There are some common reasons for this problem (discussed in depth below).

When the exhaust gases are not flowing into the combustion chamber properly, the P0400 will be stored in your Patrol’s PCM.

P0400 Symptoms: Nissan Patrol

In the Patrol there are usually no noticeable symptoms with P0400. The most common are:

  • check engine light
  • Increased engine emissions
  • Slight increase in combustion temperature

This code is a common reason why vehicles fail emissions inspection.

Nissan Patrol P0400 Causes + Diagnosis

P0400 Diagnostic

Here are the most common causes of P0400 on the patrol and a great diagnostic command to use. You will need a good scan tool to command the EGR solenoid to open or close. We’ll first cover what you can do without one.

Check the EGR system wiring

Check the wiring to the EGR valve and solenoid for any apparent signs of damage. Look for burned, cracked, or broken wires. If there are, you will have to repair the harness.

Examine the harness where it connects to the EGR valve. Make sure it is plugged in securely and that the pins are not damaged or corroded.

Check the vacuum lines

There are two main types of EGR valves, vacuum controlled and electronically controlled. Most newer engines use the electronically controlled type.

Depending on the model year of your Patrol and the type of engine, it could have one or the other

If the vacuum lines go to the EGR, make sure they are not cracked or leaking.

Check the EGR valve with a scan tool

You can command your Patrol’s EGR valve to open and close with a good scan tool. When you do this, the engine should react. He should at least stumble momentarily and even die.

Watch the following YouTube video. It lasts 3 minutes and gives an excellent idea of ​​how to test the EGR system with a scan tool.


The P0400 on the Nissan Patrol is most likely caused by a bad vacuum line, wiring problem, or the EGR valve.

If there is anything you would like to add that might help the next person who reads this article, please leave a comment below.


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