2002 Pathfinder - mysterious ECU ... idle-issue

[Matce]

Hey guys,

my buddy dropped off his 2002 Pathfinder a while ago to have me take a look at it. I'm doing Toyota-stuff for 18 years so fairly experienced with all automotive stuff.

This Pathfinder however has me puzzled! It had a bunch of issues that are fixed, but there is still a problem with idle. It just drops randomly when coming to a stop and recovers, so it should be IACV related. No code (at all) however.
I did my research, seems this is a common problem.
Measured IACV and the specs are good. 22Ohm respectively.

But here's the big surprise:
I took out the ECU as well since there is apparently an issue with the chip (location IC17) and I took the opportunity to also make sure continuity from ECU to IACV is fine. Here's the issue:
The ECU pinout doesn't match the diagram whatsoever. None of the 4 wires coming to the ECU is there (which really isn't possible).


This is the diagram I'm using.

SO:
Purple/Green - PIN 6
Yellow: PIN 8
Grey: PIN 7
Grey/Yellow: PIN 17

NONE of the colors match and no continuity.

Second:
I opened up the ECU and from my research the IC17 ship should be STA509A, however the one in this ECU is NEC UPA1560H

ECU is Hitachi GE221365-A - MEC14-345-C1-1Y29 CC

Anybody have any idea whats going on?

thanks

[mdmellott]

I'm not familiar with any of these ECU configuration differences but before I started chasing anything like that, I would first check the one and only adjustable component in the system to be sure it isn't clocked to one extreme or the other. The TPS is easy enough check and adjust for its proper setting. After that, there is an IACV relearn procedure you can easily do to be sure it hasn't lost its mind, so to speak.

[Matce]

I'm not familiar with any of these ECU configuration differences but before I started chasing anything like that, I would first check the one and only adjustable component in the system to be sure it isn't clocked to one extreme or the other. The TPS is easy enough check and adjust for its proper setting. After that, there is an IACV relearn procedure you can easily do to be sure it hasn't lost its mind, so to speak.

Hey, thanks for the reply.
I forgot... I did do the re-learn procedure twice but no luck.
TPS looks normal, but I can double-check of course.

[Slumpert]

Just tossing this out there, check out the evap system.
The evap system frequently gets triggered when decelerating.

[Buzzman]

18 year old Pathfinder with original IACV?
I wouldn't think twice about it, having gone through this problem a few years ago:
stop troubleshooting and just replace the IACV, period.
When these things are on the edge of failure, they will give you the symptoms you are describing.
Don't wait until it fails completely and then blows the ECU.
Just change it out.

[Matce]

18 year old Pathfinder with original IACV?
I wouldn't think twice about it, having gone through this problem a few years ago:
stop troubleshooting and just replace the IACV, period.
When these things are on the edge of failure, they will give you the symptoms you are describing.
Don't wait until it fails completely and then blows the ECU.
Just change it out.

That's what I thought but it measures to spec. 20-24 Ohm is the range... I measure 22. On all 4. Perfect.

[born2lse]

It's possible for the iacv to have the right ohm but still be bad. Turn the car to on with the iacv visible and make sure it extends when it received power.

[Buzzman]

It's possible for the IACV to have the right ohm but still be bad.

Exactly.
Like I said, it's 18 years old, and when it finally fails for good, it will take out the ECM.
To Matce: You can continue troubleshooting this problem with your meter and stuff, but at the end of the day, replacing the IACV is the way to go.
If nothing else, it will give the owner peace of mind knowing he doesn't have a ticking time bomb in there.
Just make sure you do a relearn afterwards.

As an aside, I'm a little surprised it isn't throwing a code.
The check engine light is not on for sure?

[Matce]

It's possible for the IACV to have the right ohm but still be bad.

Exactly.
Like I said, it's 18 years old, and when it finally fails for good, it will take out the ECM.
To Matce: You can continue troubleshooting this problem with your meter and stuff, but at the end of the day, replacing the IACV is the way to go.
If nothing else, it will give the owner peace of mind knowing he doesn't have a ticking time bomb in there.
Just make sure you do a relearn afterwards.

As an aside, I'm a little surprised it isn't throwing a code.
The check engine light is not on for sure?

Hey, nope, not on. I fixed a bunch of stuff before (FPR, Fuel-Damper, Leak at Oil cooler, etc)... Like I said, I'm doing car stuff for 18 years (usually high performance tho).

Anybody have any clue why my ECU pinout is nowhere close the wiring diagram!?

[mdmellott]

I got curious about this and then I got stumped as well, regarding the ECU wiring to the IACV. I have the same ECU number MEC14-345 C1 you have and the same year Pathfinder. I looked at the wire colors on my IACV and where they land at my ECU. Neither my wire colors or my ECU pinouts match the wiring diagram, with the exception of the yellow wire at pin 8 on the white connector block in the large ECU multiple junction connector. As for the pur/grn and gry/yel wires the diagram indicates at pins 6 and 17, I don't even see those wire colors anywhere in the ECU connector but I guess it's not relevant because those colors are not on my IACV either. Instead, the wire colors I have to the IACV are pur/blu, gry/blu, yel, and gry at ECU pin locations 3, 8, 17, and 30 respectively, plus the 2 voltage source red wires. There have been ECU revisions (different Nissan purchase part numbers) so I can only speculate that the official wiring diagrams did not change when Nissan changed component wire colors and ECU connector wire configurations in their part revisions. I did not open up my ECU to look at that MOSFET chip at IC17 like you did but I suspect you are seeing a revision upgrade with the NEC MOSFET instead of the Sanken MOSFET you expected to see. All the burned out ones I have seen online are the Sanken STA509A chips. I looked up the datasheets for both Sanken STA509A and NEC UPA1560H chips and found that the circuits are not exactly the same but do look the same functionally. The electrical characteristics of the NEC chip indicates that it holds up to higher loads than the Sanken chip. Of course, none of this sorts out the idle issue with the '02 you are working on but if your IACV has the same wire colors as mine then you can at least now confirm the continuity of the wires in the harness, assuming you see the same pinouts and wire colors I have found in mine. I did come across a posting from a user with a idle issue as you described and he found no electrical issues at all but fixed his problem by cleaning off an accumulation of gunk that built up on the IACV valve seat that inhibited proper air flow even though the valve motor was working properly. It's worth taking a look at since that would be a simple fix. Good luck with your diagnosis.

[Matce]

I got curious about this and then I got stumped as well, regarding the ECU wiring to the IACV. I have the same ECU number MEC14-345 C1 you have and the same year Pathfinder. I looked at the wire colors on my IACV and where they land at my ECU. Neither my wire colors or my ECU pinouts match the wiring diagram, with the exception of the yellow wire at pin 8 on the white connector block in the large ECU multiple junction connector. As for the pur/grn and gry/yel wires the diagram indicates at pins 6 and 17, I don't even see those wire colors anywhere in the ECU connector but I guess it's not relevant because those colors are not on my IACV either. Instead, the wire colors I have to the IACV are pur/blu, gry/blu, yel, and gry at ECU pin locations 3, 7, 8, and 30 respectively, plus the 2 voltage source red wires. There have been ECU revisions (different Nissan purchase part numbers) so I can only speculate that the official wiring diagrams did not change when Nissan changed component wire colors and ECU connector wire configurations in their part revisions. I did not open up my ECU to look at that MOSFET chip at IC17 like you did but I suspect you are seeing a revision upgrade with the NEC MOSFET instead of the Sanken MOSFET you expected to see. All the burned out ones I have seen online are the Sanken STA509A chips. I looked up the datasheets for both Sanken STA509A and NEC UPA1560H chips and found that the circuits are not exactly the same but do look the same functionally. The electrical characteristics of the NEC chip indicates that it holds up to higher loads than the Sanken chip. Of course, none of this sorts out the idle issue with the '02 you are working on but if your IACV has the same wire colors as mine then you can at least now confirm the continuity of the wires in the harness, assuming you see the same pinouts and wire colors I have found in mine. I did come across a posting from a user with a idle issue as you described and he found no electrical issues at all but fixed his problem by cleaning off an accumulation of gunk that built up on the IACV valve seat that inhibited proper air flow even though the valve motor was working properly. It's worth taking a look at since that would be a simple fix. Good luck with your diagnosis.

Thanks bud, I'll take a closer look, but a revision would certainly make sense!
REALLY weird that Nissan wouldn't supply an accurate wiring-diagram then, but everything is possible!
I'll take a closer look at the IACV again

[mdmellott]

My pleasure. fyi: I edited my post above. The pinouts I see are 3 (pur/blu), 8 (yel), 17 (gry/blu), and 30 (gry) not 3, 7, 8, and 30. I tried to edit this with stealth but since you posted my original quote I couldn't just sneak in the edit without my error being exposed.

[rgk]

Nice to see Buzzman is still around. ... Buzzman, you're not convinced it was the IACV gasket leaking coolant into the IACV and frying all those ECUs?

[Buzzman]

Nice to see Buzzman is still around. ... Buzzman, you're not convinced it was the IACV gasket leaking coolant into the IACV and frying all those ECUs?

Ya, I'm still around.
I don't come here that often anymore, but still pop around now and then to see what's going on.
I had five Nissans in the family at one point, but now there's only one, the Pathfinder, and it's on it's last lifeline.
I'll be retiring it before next winter. I'm actively looking for a replacement.
As for coolant leaks around the IACV housing, it's not a common issue or the main problem.
It's been a few years since I went through this mess, and when mine failed, it wasn't due to a coolant leak. It was dry.
In simple terms, the IACV gets stuck, and burns out a triac on the ECU.
If you catch it early enough, you can save the ECU.
My mistake was not knowing what was wrong, and the tech at the dealership not knowing what was wrong.
They had not seen the problem before.
I drove it for a few weeks with the bad IACV, and that led to the ECU problem.
If I had known then what it was, I would have replaced it ASAP and saved having to repair the ECU.
BTW, the dealer told me it couldn't be repaired, and wanted $1,400 for a used ECU. Screw that.
I think I paid around $250 at that time for the repair. I also think it's even cheaper now to get it done.

[rgk]

Yeah, as we can see here, the problem is fairly common. When it happened to mine I knew exactly what it was thanks to folks like you and NICO.

What's going on with your Pathfinder?

[Buzzman]

Yeah, as we can see here, the problem is fairly common. When it happened to mine I knew exactly what it was thanks to folks like you and NICO.

What's going on with your Pathfinder?

Well, 18 years of Canadian weather has finally taken a death grip on the old girl.
The drivetrain is still good: engine, transmission, transfercase/4X4 still function well.
Unfortunately, everything else that surrounds the drivetrain has gone to pot.
In the last two years, rust has really grabbed a hold of it.
Wheel wells are rotting out, running boards shot, roof at the top of windshield rusting, passenger side A pillar rusting, just to name the worst spots.
Brakes are done, A/C doesn't work anymore, exhaust is toast, rear hatch window hinge is broken,
door locks seized (can't open the truck with a key anymore).
Check engine light has been on for a few years now due to evap codes. Fortunately that doesn't affect how it runs, but it will never pass inspection.
If I let it sit for more than a week, the battery goes dead, and the battery is new, so I have no idea why it dies.
It just goes on and on.
As much as I've been emotionally attached to this thing for the past 17 years, I really just want it gone now.
It owes me nothing, so I have no regrets with it.
It's worth nothing as a trade-in, and it's unsalable as it sits, so I'll probably just take it to my local junkyard and let it go.
The tires are good on it though, so maybe I'll get $50 for it....lol

[rgk]

Old gray mare just ain't what she used to be

[Buzzman]

Haha. Except this old gray mare is blue (and brown...rust).