I have the repeating (after erased numerous times, but no symptoms) P1400 code for 1998 Nissan Pathfinder 3.3, 164,000 miles. It was throwing this same code with an older motor, and still is with replacement motor installed last week. I have 12v at the wire plug when it's unplugged and key on. 12v applied with jumper wires actuates the solenoid on both its leads. But, when I have a helper turn key to on I cannot hear or feel the solenoid activating. Is this solenoid controlled by ECU giving it a ground? Or how?

When I tested the Solenoid plug wire for 12v with ignition key on, I used the plug ground wire as ground for voltmeter and got 12v. That ground wire is the control from ECM. It should have been Open and I shouldn't have gotten 12v reading. That's why the tests shown online have the voltmeter ground lead connected to hard ground on chassis. Doesn't this indicate that wire is somehow shorted to ground all the time?

It could, or it could mean the MOSFET driver inside the ECM is blown short. The way to tell is to disconnect the circuit at both ends and ohm the control wire to ground. If it ohms infinity then the wire is good and the ECM is bad, if it ohms continuity then there's a short in the harness.

Hey you're on multiple platforms! Glad it's just not me! I cut it off at 4, but I have about 10 forums I found.

Will do, after I locate the ECM plug. Thanks!

IIRC the ECM on a '98 should be upright behind the glove box. Nico has a complete FSM for your ride, you can find the Engine Control section here:
https://www.nicoclub.com/service-manual ... 8%2Fec.pdf

Apparently the ECM is a PITA to access in 1998. Buried under driver side dash connections. See my latest test...

1998 Pathfinder 3.3L, automatic, 164,000 miles, stock. Runs real good.

So I'm having a recurring P1400 EGRC Solenoid Valve error come back after erasing codes. It reappears almost immediately after being erased. I don't have any operability issues. No other codes but one that came up after I started running the motor with the solenoid plug disconnected (for testing)...P0443 Evap Emission Purge Control Valve Circuit. But it stopped appearing after I reconnected the solenoid plug.

I looked where the ECM is to access the EGRC Solenoid ground wire and crap is that a pain to get out! So I did these troubleshooting steps to test the Ground wire resistance and the Voltage at the plug wire instead. This is after I tested the valve clicks/opens with 12v injected from a jumper wire. The solenoid appears good, as far as activating manually.

Ground Wire tests: left socket when looking at plug with lock button on top.

ENGINE COLD --
Off cold: 500 ohms
Key on cold: 1,200 ohms
Cranked idle Cold: 3,600 ohms.

ENGINE HOT --
25 minute idle warm up and short drive, and RPM revs to 3,000.
Off: 500 ohms.
Key On: 1,200 ohms
Cranked at 850-rpm idle: 1,600 ohms before revving, 3,400 ohms after revving 2,000 rpm.
Cranked and held at 2,000 rpm (in Neutral) for 60 seconds: 1,850 ohms.


### VOLTAGE tests ###
Power Wire: right socket.

Using ground wire on solenoid plug (motor cold) --
Off: 0.01v
Key On: 11.9v
Cranked: 14.3v

Using chassis ground frame bolt (motor hot) --
Off: 0.07v
Key on: 12.4v
Cranked: 13.7v
- Battery terminal as ground had same results.

If nobody knows I'm just gonna ignore it because I dont have emissions tests here and it shows no driveability issues either, so likley unimportant.

But I kinda wanted to understand if my EGR is being left open to exhaust or closed, with the signal from the solenoid as-is. Anyone know by chance?

Thanks!

I don't know how you're ohming the circuit with the engine running and power applied, that's meaningless (and can blow up your meter). The only things that matter are that the solenoid coil isn't shorted, the Blue/White wire has integrity, and the ECM driver works and has integrity. This isn't rocket science. Ohm the solenoid coil, if it's something reasonable that isn't near zero then it's okay. Power the solenoid and make sure the orifice goes from blocked to passing. Ohm the wire disconnected from the ECM and it should read infinity. If all of those things are true then your ECM is bad. Screwing around just because the ECM is a pain to get at is just going to leave you writing long posts and scratching your head over what should be a simple diagnosis.