Mike88SE

Hey all! Refreshing your memories I have a 2001 Maxima 5 speed. Last week I was driving home and turning onto my street realized I had no power steering. Well naturally but that's bc the engine had stopped running lol. It cranked back up easily and ran fine. I let it idle a few minutes after I got home to see if it would do it again. It didn't I drove it the next day and it was fine. That night tho, it died several times at red lights. I have a scanner but there were no codes. I drove it next day and it was fine. Next day I got in and there was no power to anything. That turned out to be the battery 120amp fuse/fusible link. I replaced that and had power again. But it also had a crank/no start. No codes. Later I tried again and it started but would die immediately w/o giving it some throttle. I had left the scanner on and noticed it read a PO505 code when cranking or running. You know the one. No code when not running. Weird right? .Then the code showed up officially. I looked online and found that a lot of people have had the IACV take out the ECU when it goes bad. Scary. Also crazy. I'd never heard of a bad IACV damaging an ECU. Apparently it's just 2000 and 2001 Maximas. Apparently a bad IACV can short and burns up some kind of MOSFET chip or driver in the ECU. Somebody must have screwed up at Nissan. I have my ECU out now and it looks perfectly fine. No burnt smell and that chip looks like new. I've read enough and seen enough pics of fried parts that I believe this really happens but nobody gave a good explanation of how/why this happens. I'm going to install a new IACV and hope for the best. My car has always had a good steady idle at around 700rpm.
The blown fuse bothers me a little but I suppose fuses do blow sometime. All my critical wiring points look good. The battery and cables were replace about a year ago and the alt seems to be fine. I can't see how that would be connected to the IACV/ECU issue anyway but then I'd never heard of a bad IACV taking out a computer.
BTW I plan to bypass the coolant going to the IACV. I'm not sure what purpose those lines serve but bypassing them was something pretty much everyone did in the z31 community. I can't imagine any useful purpose the coolant serves but I'm sure Nissan must have a reason for it.
If you have any thoughts on any of this I'd like to hear them.

maxiiiboy

I suggest you read the document on ECU failures (link in my signature, 3rd link from top).

Mike88SE

Thanks, so this is a real thing. I skimmed through it but I'll give it a good read later. My STA509A looked perfect so I'm just going to replace the IACV and see what happens. Good to know others have bypassed the coolant lines. If that burnt fuse was just some random car weirdness I should be good.
Tip for anyone who hasn't removed and installed an ECU. Place a thin towel or sheet of paper under the ECU when you reinstall the two rear 8mm mounting screws. Those are a little tough to get started and if one falls in the hole... it's gone

krismax

iTrader: (15)

I typed this in another thread

"If the p0505 goes off on a 00-01 most of the time IACV and ECU needs to be replaced at the SAME time. With OEM IACV and verified good ECU.

Nissan screwed people over with this. Should be a recall. I find many cars in junk yards from this. G20,pathfinders,maxima,I30,QX4. With the ECU's fried.

It throws other codes when the ECU is going bad. I just replaced two IACV and two ECU's on a i30,before i got the winning ticket.

Replace either or and there both a goner. Even turn the key forward and the engine not on, for a few minutes the ECU will fry the IACV. The ECU doesn't even show signs of being bad. Doesn't have burnt chips or it doesn't even have to smell. To still be bad.

This car has 74k miles on it. And the coolant can leak in the IACV even at 50k. And the motor mounts ,another disaster . Cut the plugs off them."

By the way i have had two cars that did this.And as i said it can happen to low mile cars to. And it isn't just 2000-2001 maxima's and I30's

By the way rock auto has the OEM IACV it's around $112

My ECU and IACV looked perfect to and car runs good.You need to replace BOTH. What i mean is by FRY ,is either or almost kind of puts a Virus in the IACV and the ECU. If the Good IACV is used with a bad ECU for one minute it's gone. And vice versa,when you have the P0505 code,it's done.

This is what i did with my i30 .

Person i bought it from said the IACV was replaced. And the ECU looked good inside.Bought it ,and drove home less than a mile. Code was on for that half mile .
Ordered a IACV (OEM),put it in. Then without even driving it,the code came on again. Checked ECU, looked fine.

Then a put another ECU in and after 116 miles of driving the code came on again. Then i ordered a 3rd ECU and IACV and replaced them at the same time.Car has 144.5 miles on it no codes so far.

Battery was unplugged for hours and a bypassed the coolant the first time and the motor mounts.

The point i am trying to drive home is. If the P0505 code is IACV or ECU related. You must replace both with a good part.

krismax

iTrader: (15)

This is why it happens the antifreeze leaks in the stepper motor and causes a power surge.

Look at these pictures that green white stuff in dried antifreeze. It gets by the gasket and even leaks in the engine. Everybody with a car that has this design SHOULD BYPASS IT.

Mike88SE

Thanks for the info. My IACV doesn't look like that. It's clean. I understand you have strong feelings about this due to experience but in my research I also found cases where people just replaced the IACV and had no more problems. It is possible that the IACV just went bad in the way IACVs usually do. My ECU looks great, no visible damage to the driver/chip and no burnt smell. If it looked or smelled the least bit suspicious I'd replace the MOSFET part. I don't even have the $200 to get my ECU repaired and. I've repaired ECUs in the past that were more complex than this one looks. The IACV is all that is getting replaced for now. No offence or disrespect but I don't think this computer can get a virus. The MOSFET driver is directly related to the function of the IACV. If it didn't get shorted out then it should be fine. And it's a common part that is available at any good electronics store for 10 - 15 bucks. It has what... 7 through-hole legs/posts that are soldered to a PCB. If the PCB and nearby components are good that would be a breeze. I would use a friend's soldering station tho I'd try that before spending $200 to have the ECU repaired bc replacing that part is almost certainly all the repair shop is going to do. .
If it turns out the ECU is bad I'll post that and add it to your experienced advice and say yep you were right. And don't get me wrong, I appreciate your post and info.
BTW there was no way I was going to reattach the coolant hoses. I'd always wondered what the thinking was for coolant running through an IACV or throttle body so I googled it and found a thread on a mechanical engineering forum tossing out possible theories. None of them saw any really good point in it.

krismax

iTrader: (15)

I am not saying it is literally getting a virus. But it is almost like that.

And i didn't use the cheap IACV or just replace the Motor.

My ECU's looked perfect too ,no smell.

To bad there's no way to check an ECU,off the car.

Like i said MOST of the time. Sometimes it is a different case,like you said.

It;'s to bad Nissan got away with this one and they know it.

Darren Buckley

Just a quick point the coolant hoses are there to melt the wax pellet in the throttle body because the intake plennum never gets hot enough due to it being plastic.My Max wont learn idle with hoses bypassed I tried the mod several times with same results erratic idle it must be the Irish climate.

Mike88SE

Gotcha now about the something like a virus. OT for a minute here... I've read about some of the newer cars with really sophisticated computers getting a virus or maybe malware or a highjack would be more like it which is crazy.
Anyway yeah I'll be taking a chance here but I don't have much choice. The more I read about that MOSFET chip the more it seems it is there specifically for the IACV. I crossreference the Hitachi IACV and it seems they used the same one from 2000 to 2011 in Maximas but only 2 years for the I30. From what I've read here the 5th gen Maxima is actually 2 slight variations? If the same IACV was used for 12 years then Nissan must have fixed the issue on the computer end. But yeah so many people have had this problem and the electronic motor mounts on the auto tranny cars Nissan should have had a recall or a TSB at the very least. Maybe they did in a way. I got this from Dorman:
Anyway I'm really hoping mine was just a bad pintle or whatever mechanical issue that causes an IACV to quit working. I never had any surging or high idle so fingers crossed.
Sounds as good as any explanation I've heard. Some of those engineers I mentioned were speculating that the coolant prevents the throttle plate from freezing but it didn't go over well. If it's cold enough to freeze a throttle valve then there's nowhere I really need to go except somewhere warmer. Back on the z31 boards in the 90s the subject came up at least once a year. I'm in SE Tejas (Houston) so cold weather is not an issue I have to worry about anyway

krismax

iTrader: (15)

I am using a 01 maxima ECU(gets rid of EGR) this time in my 00 I30. And rockauto has the same Hitachi part that a bought for my 01 maxima and my 00 i30?

Yeah all the cars i have seen with this,tend to be 00 01.

And i don't understand the learning idle thing? My idle was perfect both times i did this. Didn't have to do a relearn .

My 01 max has almost 3k on the ECU.

01bluemax

When I had that code, all I did was replace the IACV. It's been a year and that code hasn't come back. I feel I got lucky.

cdoublejj

usually you have to replace the IAC, send the ECU to a 3rd party to solder on some new components and replace the throttle position sensor since they are all the same circuit. normally when you replace just one. one of the other 2 components (Also bad) cooks the new part and or ECU again. mine never just died, i'd be checking battery terminals and grounds. a relearn is just considered best practice and helps the ECU adjust to any of the new sensors if it needs to.

Mike88SE

I'm seeing two types of TB gaskets. Which one is it or is it both?

krismax

iTrader: (15)

It uses both. there's a steel piece that goes on the IM first. And that's the top gasket,recessed in the IM.Then the lower gaket goes between the steel piece and the TB.

I just take the steel piece out . But i keep Both gaskets

Mike88SE

Thanks! Now to find a parts store that stocks them other than rockauto. BTW I bought a cheap ($25) IACV on ebay and then I thought... maybe I better get a Hitachi. The cheap one looks exactly like the one that was on there right down to the numbers & letters. The Chinese are making some great fakes I guess. I think I'll still wait til the Hitachi gets here and use that one. This isn't a hard job but it isn't something I'd want to have to do in the freeway breakdown lane.

krismax

iTrader: (15)

I have always reused those gaskets.

Genes1s

iTrader: (5)

@krismax

whem you used the 01 ECM to get rid of the EGR, did you pass the smog? I got P0400 that I couldn’t resolve and I think my ECM \ harness isn’t sending the signal.

krismax

iTrader: (15)

I don't have a smog check in new york only codes.

And the EGR makes the exhaust dirtier and PCV,with a car as old as yours. It pollutes more. I have been taking 00-01 intake manifolds off for ,over 10 years. The PCV valve over time ,collect more and more oil from the valve covers.

Added to the fuel dumping, the exhaust in the intake manifold. This all get sent to the engine to be burnt again..This all pools in the back of the IM. When you step on the gas it sloshes back and forth into the engine. This causes the studdering and the driveability issues some have.

The PCV oil has to go somewhere ,but it should never go in the IM. (that's why i use a water oil seperator and unhook the hose going to the IM)

But they know people won't empty the water,oil seperater.

I think it's cleaner to have no EGR.

Mike88SE

yep you were right... apparently. I put the new Hitachi IACV on and started the car. It idles at around 1300. Code PO505 pending. Looks like the ECU is bad unless I was really unlucky and got a bad IACV. I don't have $700 for a new ecu, IACV, and programming the key so I may just sell the car.

01bluemax

Use a salvage yard ecm and get Nissan Data Scan to reprogram the key. It'll save you a bunch of money.

Mike88SE

I can't trust a yard ECU. For one thing there are very few manual transmission Maximas of the right year. And the Maximas I saw last time I went looked had good bodies which could mean they were there for mechanical problems that would have cost more to repair than the car was worth. I'd bet a few have ended up in the junkyard due to this very problem. Appreciate the suggestion though. I'll have to look into Nissan Data Scan and see what that is and how expensive.

Mike88SE

Short update. I drove the car around a bit today. The idle came down to the 900 range. The car ran great. The engine light came on though and the same code was pending then went away and then came back.

krismax

iTrader: (15)

Get a ebay ecu they have them . About $299 to $349 shipped. modulemadness

And send your IACV back . and get another .

Switching one or the other will be, A FAIL.

NDS2 is about $60 and a cable another $15-20 then you just put it on your laptop I have it and have programed many ECU's and keys.

Takes about 2-3 minutes to do.And that includes plugging the cable in and turning the laptop on.

krismax

iTrader: (15)

You can drive hundreds of miles with no Codes or symptoms . But once one is bad ,both are done.

Raxis

coolant leaking into the IACV solenoid can cause the ECU to short a mosfet yes it happened to my maxima once, ecu replacement and reprogramin o keys and a new iacv later, there is a protection fix for this tho, on the cable for the IACV solenoid find the 2 12v + wires cut and install two fuse holders and fit them with 7.5a fuses, this will protect the ECU from burnout if the coolant passage should ever leak into the IACV solenoid, its better than bypassing the coolant lines(as some people do) to the IACV, as the metal spring that holds the plastic cam inside the IACV is bi-metalic and changes tension with heat from the coolant which sets your cold and hot idle speeds in conjunction with your ecu(assuming everything else is set correctly/no codes and the ecu isn't being a pain about something else)

never mess with the bi-metalic spring, you will gack it, its tuned very specifically, don't put it in backwards, don't try and tweak it for more or less tension.

krismax

iTrader: (15)

I have been bypassing these coolant lines on TB for over 15 years no idle problems.4th and 5 th gens.

Will this also protect the IACV from the ECU?

I like your idea though to check ECU's ,to see if there bad.

Raxis

Aye, you can bypass the coolant, and it can have no problems, the ecu on these things seems to be able to compensate for a great amount o things(including a failed ref crank position sensor not working, and a bad maf, and still run fine, infact the ecu's ability to compensate for alot of problems all together is part of what makes diagnosing alot of things without a scanner difficult on some of em.

but if you wanna keep it without the bypass the fuses protect the mosfets in the ecu from a direct short in the IACV, but no, once the ecu has shorted fets, it'll blow a new IACV all day long because a shorted ecu mosfet will send full 12v down the signal lines cooking the new IACV solenoid.


apparently this also happens with the electric engine mounts when they short, I wonder if the same fuse setup can be applied to them