The engine light appeared Code P0400?

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.

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.

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.

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?

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?

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?

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?

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?

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.