How JustAnswer Works:
  • Ask an Expert
    Experts are full of valuable knowledge and are ready to help with any question. Credentials confirmed by a Fortune 500 verification firm.
  • Get a Professional Answer
    Via email, text message, or notification as you wait on our site. Ask follow up questions if you need to.
  • 100% Satisfaction Guarantee
    Rate the answer you receive.
Ask Pete Your Own Question
Pete, Technician
Category: Car
Satisfied Customers: 29040
Experience:  17 years automotive training and experience.
Type Your Car Question Here...
Pete is online now
A new question is answered every 9 seconds

Infiniti G20 P0400 DTC

This answer was rated:

Hello Infiniti Mechanic: I'm getting a P0400 DTC. Per the function check instructions in the Infiniti repair manual, I scanned the engine coolant temperature, and it is above 70 C, so I'd like to perform the procedure for malfunction A. This procedure asks that the engine be revved up to 2000-4000 RPM, while visually checking the EGR valve. The repair manual also shows a cutaway, but that appears to be UNDERNEATH the vehicle. Is this correct? Should the EGR valve be close to the engine block? If you have a picture on a '96 G20, that would be helpful. Thanks.


Update: I found the EGR valve ( behind / below the air intake hose that runs into engine block. Will send a follow up question after I've had a chance to check it.

My name is XXXXX XXXXX I am a professional here at Just Answer. I noticed that your question was not getting a response and thought I would ask to see if you still need help with this.

If you still need assistance with this after the check you perform let me know and we can continue from there.

Thanks Pete
Customer: replied 4 years ago.

Here are a couple of pictures from my car, as well as a stock photo of an EGR valve for the Infiniti G20. Please answer / confirm / correct the following information to make sure I have it right.


1. The vacuum line is to the metal section of the solenoid. This is what actuates the valve. Correct?.

2. The 2 holes shown in the stock photo are simply for metal hangers. Correct?

3. On the valve, which is the input from the exhaust, and which is the output back to the engine? Of these, which is more likely to be clogged?

4. If these are clogged, how do I determine whether the valve can be cleaned, or does it need to be replaced?

5. It appears the black rubber air intake manifold (approx 4" with many connections) will need to be removed, and possible the EGR BPT valve will need to be removed to gain easy access to the EGR valve. Any issues / dangers / potential problems with doing this?



1.The vacuum line is what opens and closes the valve here on this vehicle.There should be vacuum on this vacuum hose/line with the engine revved up above 1500 to 2500 rpm and the valve should be seen to lift open slightly.

2.The two holes I see in the pictures above should be for mounting the egr valve to the vehicle.

3.My info doesn't show exactly which is the input from the exhaust or output to the intake/engine,usually you can follow each connection from the valve to see which runs to the engine possibly the intake and which runs to the exhaust to find out.The intake/engine port side is most common to clog.Usually the threaded port on the valve is for the exhaust side.

4.One way to test the valve is to run the engine at idle,then use a vacuum pump on the vacuum port on the valve and apply vacuum (usually 12 to 15 inches of vacuum).If the valve is operating properly as well as the ports the engine idle should stumble possibly even causing the engine to stall out.If it stumbles only slightly see if the diaphragm on the bottom side of the valve is opening with vacuum applied,if it is not then the valve is faulty needing replaced.If it is then most likely the engine/intake port is restricted needing cleaned out.In some cases you may have to remove the engine side of the port components to clean out the carbon build up causing this issue.I have had some success with wire coat hangers as well to clean the port.

My info isn't very clear or specific unfortunately for this model on how this valve is removed/replaced.It tells me to remove the bolts from the valve and remove the valve as it is skipping all of the rest of these components that may need moved out of the way to gain access to the valve.Usually I will go by look,if there are components blocking access to the valve and there is no possible way around them then I remove them.

I hope this info has helped,if you need anything else let me know before rating my help here.

Thanks Pete.

Pete and 5 other Car Specialists are ready to help you

I'm just following up with you to see how everything is going. Did my answer help?

Let me know,
Customer: replied 4 years ago.

Thanks for the follow up. Since my car is running, this isn't an urgent issue, so I've only been studying it, and not acting yet.


First, to digress, even though it doesn't directly address the P0400 code, what impact does the PCV valve have on this? It has very easy access, and the part is <$5, so I'm thinking of checking if that is clogged. My only concern is stripping the engine block threads. Is WD-40 safe to spray on these threads?


Second, I've attached a couple of diagrams of the EGR setup on the Infiniti G20. Unfortunately, the diaphragm can't be seen visually due to the valve's orientation. Is it safe to stick a finger underneath the valve to feel the diaphragm while the engine is being revved up to 2000-4000 RPM?



The PCV (positive crank case ventilation) is used to vent the engine pressure.The EGR 9exhaust gas recirculation) valve is to recirculate any un burned fuel vapors entering the exhaust back into the engine.The PCV is a different venting system then the egr and usually from all the vehicle I have seen wont cause this issue unless it is plugged and no vacuum is present on the engine then there would be no vacuum to the egr valve to open it.You can check this usually by removing the vacuum line from the egr and revving up the engine and feel if any vacuum is present on this line.If there is sufficient vacuum (12 to 15 inches) then most likely the pcv is o.k. but if there is little to no vacuum then the pcv may be restricted needing replaced.

If you can feel the bottom of the diaphragm easily on the bottom of the egr valve with the engine off without having your hands or arms in the way of any moving parts then you should be able to rev the engine up to feel if the valve is opening with no issues.You just need to feel the bottom to see if it lifts up when revved up.

I hope this info has helped,if you need anything else let me know before rating my help here,thanks Pete.
Pete and 5 other Car Specialists are ready to help you

I'm just following up with you to see how everything is going. Did my answer help?

Let me know,
Customer: replied 4 years ago.

Thanks for the follow up. I just bought a vacuum tester, so I'll perform the tests and report the findings back to you. Hopefully soon.

Let us know if you need anything else.

Thanks Pete
Customer: replied 4 years ago.

So after going through all the vacuum testing, trouble-shooting, and learning diagrams of my entire vacuum system, the problem was as simple as a cracked hose at the bottom of the ERGC-BPT valve (not the EGR valve).


I ran my fingers over all the hoses EXCEPT this one. The repair manual's trouble shooting procedure called for removing the EGRC-BPT valve, and testing it for leaks, and upon attempting to remove it, I found this crack (see picture).


Thanks for all your help. BotXXXXX XXXXXne is that the problem is solved!EGRC-BPT Valve Cracked Hose

Thats great to hear.Let us know if you need anything else in the future.

Thanks Pete