Yesterday, out of nowhere, my Maxima would not rev pass 2700 RPM. This happened during highway cruising too. So, I pulled over and ran the scanner and I got P0403 (EGR Circuit Malfunction) and P0505 (IACV). I cleared it and and the P0403 came back right away while the P0505 went away.

Took throttle out and removed the IACV and looked cleaned. Finally took the EGR valve and the solenoid out too. All passages looked cleaned.

I followed the FSM to trouble shoot it.

1. CHECK EGR VOLUME CONTROL VALVE POWER SUPPLY CIRCUIT. This is basically checking the voltage between pin 2 and 5 to ground (use body ground) to see if you get 12 V running thru there. No Problem found
2. I did the test #1 on IACV harness also. No Problem.
3. Checked the Resistant on the EGR Selenoid. This is basically between pin 2 and 1, 3. Also between pin 4 and 5, 6. It should read about 23 ohm. No problem found.
4. I did the same thing for IACV selenoid. It should read about 22 ohm. No problem found.
5. Since the EGR selenoid passed test # 3, I should be able to see the plunger moves when powered thru ECM. I plugged in the EGR harness from ECM to the EGR valve and turned the ignition key on (do not crank it). The plunger didn't move. Took the plunger out exposing the shaft and retested, same thing. So I was like
6. Did the same thing with IACV and the shaft moved, so IACV is all good.
7. For the heck of it, I plugged in the IACV harness to the EGR selenoid (they are identical and have the same principle) and EGR selenoid was functioning perfectly. The shaft moved out then few second later moved back in when the ignition key was off.

So by now It seemed that the EGR Selenoid was good.

I went ahead doing continuity test between the ECM main terminal connectors to the specific F4, F71 EGR connector. I had to create about 10 feet of wire jumper to be able to do it on every pin (1,4,3,6) on the EGR connector to pin (9,10,18,19). FSM showed it in detail. All pins had good continuity except pin 1 to pin 9, it was dead silent. So, I though maybe the connector itself, checked the connector itself and it was good.

So the problem seemed to be an open condition on the ECM harness at pin 9 which is one of the signals to the EGR Valve stepper motor. I guess basically there is no feedback between the EGR Valve selenoid and ECM and that caused the selenoid to not functioning and ECM went to limp engine mode.

Well today, I did more checking and there was a plug connector (by high pressure power steering line) that loosed its connection. Apperently someone in past before my time fixed something on this juncture and I could wiggle the connector and would loose/gain connectivity between the EGR connector and ECM plug.

Fixed that and all terminals got connectivity now, but the EGR selenoid still didn't move when I put everything back together and turned ignition key on/off.

Here is the video of the test with both IACV and EGR selenoids connected to its connector. You can see that the IACV seleoid worked and the EGR selenoid didn't
https://www.youtube.com/watch?v=168j_js9KyQ
Here is the video of the reverse test. I powered in the EGR selenoid using IACV harness and vise versa. The EGR selenoid worked and the IACV selenoid didn't.
https://www.youtube.com/watch?v=7pl16BvH6Sc
I did these tests twice and resulted the same.

So it seems like the EGR selenoid is OK since I could power it using IACV harness and the IACV selenoid that worked in its harness didn't work with EGR harness. Seems to me that the EGR harness is still at fault even though the circuit is all good now?

I'm stuck, any help is appreciated.