the engine light appeared Code P0400?

Hello,

Since replacing the component did not fix the issue, it could be related to the wiring circuit. It could be an issue of not getting the proper signal.
To figure out what is causing this you will have to take a little deeper dive.

I have attached the trouble shooting guide for the code P0400 below. Follow the steps and it should help you identify the issue.

Please let me know if you have any questions.
Thank you.

Sorry for the late reply. I checked the fuse that connects to the EGR, and it's not blown. Do you suspect that it might be a dirty manifold connected to the EGR Valve?

I've also noticed that at idle, the car vibrates a lot. I'm not sure if that has to do with the EGR system but thought it might be related. There's also a very slight rise and drop in RPM while at idle, but it's barely noticeable.

Additionally, all the wiring to the EGR Solenoid is good. It's receiving power, holding a vacuum, and makes a "click" when powered.

However, the radiator fan turns on after driving the car for less than ~0.2 miles. I'm not sure if this has to do with the EGR Valve not recirculating gas to cool the engine.

Dirty EGR can impact the idle and overall drivability.
It will be a good idea to clean the EGR valve and the pipe (if it hasn't been done in a while).

You can also follow the diagnostics steps that were provided. It can help determine the cause for the code.

https://youtu.be/DqUCbbKdWf4

The EGR valve is new, so there's no carbon build-up that is leaving it stuck open or closed. I am a little confused as to what pipe you're referring to.

I am referring to the EGR tube. Also keep in mind that the EGR solenoid can trigger the code as well. Unless you already have, I would suggest you to go through the diagnostic steps, which covers the testing of the solenoid as well.

The EGR tube is clean and the EGR solenoid is working. I’ve tested almost everything in the documents provided. The EGR valve works as expected, the EGRC-BPT is working, and the EGR temperature solenoid is working.

The intake and exhaust to the EGR valve does not have any carbon buildup (as far as I can see). However, I am still unsure if the intake manifold is clogged up and keeping the EGR valve closed. I think the EGR valve could be closed because there’s a high amount of NOx (according to a smog test) and the engine is knocking, but I’m still not sure if it really is closed or not

I am also worried if the exhaust system needs cleaning of some sort for the code to go away. I’ve heard that sometimes the exhaust system needs cleaning for the P0400 code to go away.

It is possible to have the P0400 code for dirty exhaust, but that is not very common and the exhaust has to be extremely dirty/clogged.

I recently started working on this problem again. However, this time when I scanned for issues, the P0400 issue was gone and a P1400 had popped up indicating something was wrong with my solenoid. I checked to see if there was suction from the intake to the solenoid and all checks out. The pipes from the solenoid to the EGRC-BPT is all good. The pipes from the EGRC-BPT to the EGR all seem fine as well and are not clogged. None of the pipes are cracked either.

However, I tested the voltage to the solenoid, and it showed 5.0 volts being powered to it. I’m not sure if this is too low since other people show their solenoids being powered at 12 volts.

Additionally, the OBD scanner mentioned a DPFE Circuit Low Input. I have never heard of this, and I also don’t know where it is on the Altima. I also don’t know how to diagnose a DPFE Circuit.

Main questions being: Is 5 volts too low for my EGR solenoid, should I be concerned about a DPFE Circuit, and how do I diagnose a DPFE Circuit Low Input?

The typical signal voltage is around 5V so that should be ok.
Take a look at the trouble shooting guide for the P1400 below.

Keep in mind it is possible that the ECM is not providing propter signal, due to being faulty. But that is something you want to check last.

So, I referred to the air continuity diagnostic and tried it. I connected a battery to it, and it clicked. Additionally, the air passages changed from A/C to A-B. I wanted to see if the harness to connect to the solenoid was good. I first left the harness unplugged and checked that the air passage was from A/C, which it was. Then I plugged the harness into the EGR solenoid, and the air passage was still from A-C. Since it’s powered, it should’ve changed from A-B and not stayed from A/C, right?

I kept the car in ignition and made sure 12 V was being powered to it using the posted pictures above, and the harness gets about 11.7 volts, which is sufficient.

Does this mean that there isn’t a proper connection between the EGR solenoid and the harness that connects to it?

That's correct it should have changed from A-C to A-B.
So if you get 11.7V to the connector, that is enough as you know.
How is the condition of the connector? Any loose parts?

The condition of the connector is good and doesn’t have any loose or bent parts.

However, I wanted to see if the solenoid would click if it was powered by the harness. I first put the car into the ignition. I hooked wires going from the harness to the solenoid and it never clicked. I also checked my meter to see if there was a solid connection between the harness and the solenoid, and it was showing 11.7 V which is sufficient. It never fluctuated when I measured it.

But when I connected the solenoid to a 9V battery, it clicked and changed the air passages as expected.

Could this mean I might need a new solenoid or is this something else?

If you are getting voltage to the solenoid and it is not clicking then the issue is likely solenoid.

Does the issue still lie within the solenoid if it is drawing too many volts?

When I connected the solenoid to the harness, the voltage between the two dropped from 11.7 V to 12.8 mV after the two were connected. It also did not click. This did not happen when I hooked up the solenoid to a 9.0 V battery.

When I connected the solenoid to a 9.0 V battery, the voltage between the two only dropped to ~7.5 V, which is typically normal. It even clicked too!

What could this possibly mean?

That is strange. If it clicks on 9V it should click on 12V as well. Have you checked the ground of the solenoid harness? If the gourd is not good, then this could have this issue.
When you check the voltage on the harness did you check between the pins?

The ground to the harness is good. I checked the voltage using ground and also checked the voltage across the pins. Both show ~12 V.

Ignore what I said about "the ground to the harness is good". I meant to say that it showed 12 V when I checked the voltage using a ground (not the one connected to the harness).

I got a new solenoid and that appeared to not work either. I was wondering, where is the grounding wire is for the solenoid? Is there an image or diagram for where the grounding wire is? How can I check if the grounding wire is not bad?

One way to check to see if a wire is good, you can check for continuity using a multimeter. Check for resistance of the given wire. If the wire is good, it will show a resistance value, if it shows out of limit (OL) then there is a break in the wire somewhere.

Here is a helpful guide:

https://www.2carpros.com/articles/how-to-check-wiring

See attached for the harness diagram below.

Is it possible to provide which pin the ECM uses for giving the signal to the EGR solenoid? Or if you don't know which pin it is, do you know how to remove the plastic cover on the harness?

There is an image attached below. Unscrewing the bolt allows you to unplug the harness, but it doesn't necessarily take off the plastic cover.

See attached for the ECM pinout.

I tested the wire connecting from the EGR solenoid to the ECM and it is showing that it is "out of limits". Just to make sure that there is actually no signal coming from the ECM, I tested to see if there would be voltage from the wire connecting from the ECM to the EGR solenoid, and there was very little voltage despite the car being on idle. I checked the images you provided me, and it mentioned that the wire connecting to the ECM is supposed to have 11-12 volts when idle. I checked this by connecting one of the probes to the wire connecting to the ECM and connecting the other probe to ground. It showed less than 30 mV all the time.

TLDR; the wire connecting to the ECM showed it was "out of limits"

Since I know that the wire has a break, how can I go about locating this? Do I need to rent or buy specific tools for this?

You can manually trace the wire that has the low voltage. Keep in mind that many times these wires are only available as a complete harness.

You might find this guide helpful:

https://www.2carpros.com/articles/how-to-check-wiring

I manually traced the wire, and there was no break in the wire according to the tool. I even made sure the pin to the ECU was good using the wire tracer, and it was. I don't understand why the multimeter it's showing 0F/open when testing the wire. Does this mean the ECU is faulty or is there something else I'm missing?

So, I think this is a flow problem. The EGR exhaust supply passages are blocked and need to be cleaned, please remove the EGR and look with a flashlight or start the engine to see if exhaust comes out. Plug the vacuum side the best he can, you should hear the exhaust through the EGR port.

I checked all the EGR passages, and they’re all good. There is very little carbon buildup. This was the first thing I checked. I’m very certain it is an electrical issue since turning the car on didn’t change the air passageways on the solenoid when it should’ve.

Can you tell me which wire you traced on the ECU. I will see if I can find the technical data on it.

I checked a different pin this time, and it showed that the wire is actually closed. So now I know the issue doesn't lie within the wire, but rather with something else.

I plan on replacing the ECM, but is there some other sensor besides the EGR Temp Sensor that I should check before replacing the ECM?

Also, if there is nothing else, I should check, how do you replace the ECM on this car? Do I have to buy a new/used ECM and get it programmed by the Nissan dealership, or can I use a different ECM with the same model number?

Replacement ECM will have to be programmed to your car, regardless of whether it is new or used.
Most cases there are several different ECM that can fit a given car. Best course of action would be to find the correct part number by calling the dealer with your VIN.

Is it possible to reprogram the immobilizer of the new ECM with a tool of some sort?

Or is it possible to reprogram it like in the video below:
https://youtu.be/tRbwMsUw8A8

I don't really want to go to a dealership and give them $200 to reprogram the ECM.

That procedure might work. But it does look like for newer vehicles.

I think that procedure only works on a Toyota/Lexus.

Is there any other sensor I should check before I change the ECU?

Also, is there a tutorial on how to program an ECU and install it into your car? I plan on getting an ECU with the same serial number, but I don't know how to reprogram it and install it. I don't want the car to not start/run after I've installed the ECU.

I have attached the ECU programming procedure that Nissan recommends. It does require scan tool to perform.

I've been told that if I get an ECU with the same serial code, I don't have to flash it or anything like that, and I would just have to make the immobilizer work with the new ECU.

Just in case I get an ECU with the same serial number, how do I properly install it in the car? What are the steps I'm supposed to do when working with any scan tool to make the new ECU work with the car?

According to Nissan any replacement ECU will have to be programmed to the vehicle.
And the procedure is the steps that I have attached on the previous post. It shows step by step process.

Can a leaky intake manifold cause the P1400 code to pop up?

According to Alldata, these are the two probable causes that the P1400 can show up.

Exhaust Gas Recirculation (EGR) Control Solenoid Valve
Exhaust Gas Recirculation Control (EGRC) Solenoid Valve Circuit Open or Shorted