ManualMaxima

iTrader: (10)

Have a problem with a 2001 Maxima I'm helping someone on, and need some help myself!!!

First, the long story short bit. Car popped the infamous p0505 code, IACV and ECU were toast. New part and ECU repaired (By a well known ECU repair shop) then installed, idle re-learn completed I believe as she was idling properly. After 10 miles down the road the sweet smell of another burned ECU chip became apparent. Tested and IACV and ECU took and dump again. After this, we spend hours running continuity/short/voltage checks on everything; all passed. Also ran checks per the FSM concerning power steering/TPS/etc. New IACV and rebuilt ECU installed again and car still pops p0505 after this 2nd go around...mad! Haven't even driven it to do the idle relearn since i don't want to pop another IACV, we've just babied it at idle for a few minutes at a time. Note- motor mounts have long since been disconnected even before this problem arose.

Now, my questions; *And I have already read every thread on this topic I could find, but answers to these questions haven't been addressed as far as I know.

1st- I believe the IACV is shorting due to it overheating. Both bad IACV's showed no signs of deterioration in the coolant channels, just bad impedance readings. My reasoning being that the ECU is trying to make it control idle which it can't do, and is causing it to run constantly and bottom out. Is this likely?

2nd- Is it normal to hear a very faint hissing sound near the middle of the intake area on the 5th gen. I do hear what might be a vacuum leak, but can't tell if its just normal flow through the system or a leak as I don't have a 5th gen to compare it to. I've tried throttle body spray all around the area but can't pinpoint anything. Where are common areas of vacuum leaks on these cars?

3rd- Can I run the car with the IACV disconnected (I know it will stall/run bad). Basically, I just need time to have it running to do some checks without worrying the IACV circuit will short again. Will the ECU and sta509 chip have any problems with this? Don't want to disconnect only to have the chip have no place to send power to and heat up/fry. I don't think it would but want to double check.

4th- Does anyone have knowledge of items or things causing P0505 IACV/ECU problems beyond the usual list of suspects?

Finally, thank you for reading all this and for others who have posted about this issue, as it has been a nightmare for us involved. Any other thoughts or ideas would be greatly appreciated. I'm not ready to give up yet but am close...

DennisMik

iTrader: (2)

1 - No. The only reason I know for the IACV shorting out is that the engine coolant gets into the stepper motor chamber and causes the motor to short. Which brings up the question, where did you get the 1st replacement IACV from? Was it brand new or a junkyard special?

2 - Again, No. You need to track this down and fix it. I could be the PCV valve mounting gasket, they seem to deteriorate. But it could be any of the vacuum lines in that area or even the intake manifold gasket. Fixing a vacuum leak is almost mandatory before trying to adjust the idle. This and getting a check engine light for O2 sensors detecting lean conditions.

3 - Yes. With the IACV unplugged, electricity will not be flowing, so the chips in the ECU won't burn up. Burned components happen from short circuits that allow too much electricity to flow.

4 - As far as I know, P0505 is strictly the IACV. The only other thing that burns up the ECU are the electric motor mounts that the auto trans equipped cars use. I don't think that causes a check engine light, though.

When you get another IACV, check the resistance of the stepper motor windings before you install it, that way you know that the IACV is good before you start. Another thing that some people do is to not connect the engine coolant hoses to the IACV, they just get a coupler and plug the 2 hoses together and bypass the IACV. If you do this, you will probably have a bad idle when the engine is first started on a cold day. In the South, not a problem. In the North, maybe.

ManualMaxima

iTrader: (10)

First, thank you so much for your reply, I really appreciate this more than you know!

*when I replaced the IACV the first time the part was a brand new "Standard branded" IACV assembly not just stepper motor). Once I got the second replacement (Intermotor). Got 22ohms +/- 0.02 ohms across appropriate pins.

IACV original - shorted at pin 3 (OEM)
2nd - shorted at pin 4 (Standard Motor Parts)
3rd - still good / limited run time on this part (Intermotor)

I've been through the IACV circuit from ECM to IACV with a fine toothed comb so I'm positive we are good there concerning shorts/continuity. No o2 codes throughout this problem and computer did achieve readiness before previous failure.

*Coolant hoses are attached stock no leaks (not by-passed), but probably will help owner do this in the immediate future. Florida car.

* Only code ever shown is P0505 throughout this whole mess. I can feel the IACV moving when ignition turned on but it throws the p0505 within a minute or 2 of idle while idling at 1000rpm (*idle relearn not completed yet due to previous mentioned reasons)

* I'm in full agreement with you that it's time to stop and really dig deep into finding ANY vacuum leakage first. I hope that leads me to something more definitive in causing this problem.

Thanks again...

ManualMaxima

iTrader: (10)

Checked all vacuum lines all good. Throttle body has no leaks. *Believe now that what I thought was a vacuum leak is really just the sound of air rushing around the closed throttle plate through the non-functioning/non-working IACV air channel into the intake manifold (it does and should different I think).

P0505 pops up within a minute of cranking every time. I've ran all I know to do as per the Factory Service Manual. I pulled the IACV last night and checked pins again to see if its still good after the limited run time I've put on it. It tested fine/ECU still good, but p0505 still pops up. Is there any proof that aftermarket IACV's are to blame. It's easy to point to this as the problem but 2 different brands (Standard & Intermotor) not working is kind of strange to me. Is a OEM IACV a likely solution beyond just guessing..???

noahrexion

Sounds like you need to try the idle relearn in regards to the PO505.

Pin 3 and 4 are pins 8 and 7 (to ECm) respectively - both of which WILL result in an PO505. If you ohm'd those out 100% and you are good to go and your IACV is testing out GOOD prior to installing then you should be leaning towards the idle relearn. That is assuming you hear the buzzing of the motor after ignition is turned off (@ IACV of course).

Oh and for ****s, you might try letting the car completely warm up with IACV unplugged. Turn ign OFF; clear codes, plug IACV in, start car and see how it goes (for idle relearn).

TunerMaxima3000

iTrader: (4)

Sounds like you have deterioration in the their body area and coolant is getting in the motor, maybe?

I am shocked you haven't bypassed it, that is the first thing id have done.

You can simply unplug the IACV motor, it won't even change the idle on this engine in my experience, the iacv on the de-k was a complete waste of time and isn't even needed.

noahrexion

I agree under most circumstances - but it certainly does its intended duties during high(er) loads on motor (power steering, electrical, A/C...etc)

ManualMaxima

iTrader: (10)

Just in case anyone has never seen a fried portion of the ECM...

2 pics: burned leads on ECM circuit board leading to trashed chip.

Last pic: trashed STA-509 chip from short/overheat. This is the MOSFET driver for the IACV. Some blow themselves apart, and others like mine might not be noticed immediately if you only give it a quick glance. Mine has crack running through it if you look closely.

Pilm

When you turn it on after 2nd repair is the idle right and is it stable? If it is then I doubt idle relearn will fix or help anything.

BTW, have to ask, you did clear codes so you know the repair is generating a fresh code.


Agree with the other "no" answer, when I removed mine the gasket looked great and no signs of coolant getting where it shouldn't, yet it was bad. So I'm not sure how coolant shorted one of my coils but apparently it did (if people are right that this is the root cause). BTW, if it is true that this is the root cause, then your case would be extremely odd because that would mean coolant, somehow, immediately shorted one of the coils on your brand new replacement IACV, which is very very hard to believe. I wonder if perhaps you got a bad part from Autozone, maybe one of those return specials where some moron returns the bad part they remove from their car for a refund. I mean, it's just hard to believe the new part could develop a coolant leak in the 10 miles you drove, assuming you used a brand new gasket when you installed, which I know you did.


I know you said you checked all the vacuum lines and they were good, but is the hissing sound gone now or still there? If you still hear some hissing you need to track it down.


As others have said, you can do this, but this will not protect your new IACV from possibly getting coolant into the coils (coolant flows all the time whether you have it connected to the ECU or not). It will however protect the ECU should the IACV develop another short (at least until you connect it later). I guess the other thing to add is this might help protect your IACV if the problem is really being caused by something other than a coolant leak.


The only other thing I've heard is the TPS, I read all the threads when I got P0505 and some folks said you had to replace both the IACV and TPS, or the problem could come back. So I bought a TPS with intention of replacing it, but when I removed the old one and tested it, it worked fine, so I ended up reinstalling the old one and the repair was successful, so I don't believe replacing the TPS is necessary as some said. Anyway, just be 100% sure your TPS is working right (in fact, if you are up for it, take it out and measure it, both the sensor and switch, just remember you'll have to go through the PIA calibration when you reinstall).

Only other thing I'd do is open up the ECU and just look at it to make sure they did a good repair. The pictures you posted look like you had at least one blown track, so I assume they installed a jumper wire along with a new chip. Another good reason to look at the repair is to make sure they put any jumpers to the right pins, if they put the jumper to the wrong place that obviously would be trouble!

ManualMaxima

iTrader: (10)

Wow, getting a lot of good support on here from all of you THANK YOU IMMENSELY!!!

After 2nd repair: On start it instantly revs to about 1500, and IMMEDIATELY begins stepping down to a stable 1000rpm in quick fashion. (again without re-learn being attempted yet). With IACV disconnected, it idles erratically loping from 1500k-to-3000+ or so.
*I also have a simple code scanner and reset codes continuously.

Exactly! I'm not sure how coolant came into contact with the first IACV circuit or the second for that matter, but if that's the accepted failure cause I'll accept it as fact I guess. Concerning a bad part, I can only assume it might be to blame since I wasn't smart enough to test it out of the box. If it IS the cause, it sure has thrown me for one big messy confused loop (and it not even April Fools Day yet). Sure seems likely though! And yes, new gaskets were used :-)

Yes all vacuum lines are good for sure. If there is a leak it would have to be located in a relatively inaccessable spot, and checking this thoroughly would take me deeper than I want to go on a car that's not mine (ex. whole intake gasket). I will admit I'm not totally familiar with 5th gens, and it also could be a figment of my imagination, I just don't know. Its possible these cars just sound weird to me, and its actually just normal flow through the intake system (its not a loud hiss again it just sounds strange to me and reminiscent of a vacuum leak). Wish I had better knowledge to help you help me on this one, so I guess I'll just have to leave this aspect "unknown" for now.

She's gonna get run tomorrow so we will see how this goes.

Yes I've read this too. The TPS and power steering checks are really the only reason we've been running the vehicle until I figure out what's going on, since the TPS needs some heat on it to properly check some of the resistance values. It checks out just fine.

This is a problem! The repair facility tapes these repaired ECM's with tamper proof stickers that say "void if removed" on the ECM box. Because of this I haven't seen inside the box since the initial blowout. We sent the computer back to them after the 2nd ecm incident and had a good talk with the tech who assured us the fault wasn't with the ECM; and I actually do believe him.

Once again thank you very much, and sorry since it sounds like you've been through this problem before as well; but with much better success than me! The only thing left to do at this point is to just take a risk and hope that the new IACV valve works, because beyond this cause I'm all out of ideas. I'll update this thread tomorrow with the results of attempting to do the idle re-learn. My plan is to run her until hot with the IACV disconnected, complete pre-conditioning , and then connect the IACV and try to get a good result. Hopefully it will take and all this will have happy ending, if not I'm pushing the b****ch over a cliff...

ManualMaxima

iTrader: (10)

By the way, for anyone looking through p0505 threads in the future, I ran across these guys who will replace your fried STA-509 chip with their own module. Seems like a damn great idea, and cheap insurance for not having to deal with this mess ever again. Wish we had gone this route initially for piece of mind!!!


AVPRO~
"These Avpro modules sense any overload on the outputs to the idle speed valve within 10 micro-seconds and shut down all outputs to the valve for 2 seconds. The Avpro modules then retest the valve for faults. The same P505 code will show and a check engine lamp will come on until a new idle valve is installed. The part is transparent to the normal operation and recovery, as well as the relearn process. No damage to the engine controller will result."

EuroDriver

iTrader: (21)

When I had the dreaded code, I was fortunate to not fry the ECU. However, for what it's worth, I'll share my frustrations in hopes they help you out.

First, when I got the dreaded P0505 code, I ran out to Autozone for a new IACV. BIG mistake - it made matters a lot worse. After giving up, I took it to my mechanic who advised me to stick to original Nissan parts.

Second, after installing a genuine Nissan IACV, the code kept popping up, and I had a surging problem at a certain RPM range (between 1000-1500 RPM or 1500-2000, I don't recall exactly) and it would not accept an idle relearn. After much more frustration, I took it to the dealer, who diagnosed a bad ECU. Not trusting them, I took it to another shop (my regular mechanic didn't want to go there). They manually adjusted the throttle and after that, I managed to complete the idle relearn. It;s been fine since.

Here's a link to my thread when I was dealing with all of this: http://forums.maxima.org/5th-generat...r-relearn.html

After they were done, I recalibrated the TPS and it solved the surging. By the way, you'll notice I talk about replacing the temp sensors - I guess I read somewhere they can possibly trigger the P0505 code but in my case, they were a non-issue.

Hope it helps.

shaks

iTrader: (15)

I had a P0505 since I purchased my Maxima. Spent a lot of time and effort on fixing it. short story - 2 burnt ECUs and one bad IACV. Still have the code.
Long story: as I got the car I knew the code was there, so I have purchased an IACV (new OEM Hitachi) and tried to install it. Car was idling like crazy in between 1800 and 2400 rpm and revs would just bounce.

I knew it required relearn, but dealer would give warranty on it. So I swapped IACVs back to previous state. As the inspection was coming I needed to fix it and found out that ECU was burnt. Bought a used one off a member here.
put "new" ecu with the same IACV and code went away after relearn. That lasted for inspection and 3 days after that.

Next step was to fix the old - first ECU, so I replaced the chip and patched the traces myself using helpful pictures from one of the guys here, also wired in fuses for 4 main pins on the chip.

Now car is running with repaired ECU, idles at around 900 and I'm not able to do the relearn - it fails during one of the communicating stages with ECU. So code is still there.
Thanks to the help of my friends at the shop, I haven't spent too much money on the issue and was able to use their computers for free (for beer mostly).

Next step for me was to wire in two resistor right after IACV and replace the power steering switch, like TunerMaxima did with his car. I did test everything and all of the components work. But something still triggers the short.... I also checked all the wiring that is almost perfect shape for my 12 yo car

TunerMaxima3000

iTrader: (4)

^^ My code just came back.....

So either something else is triggering it, or the switch didn't actually fix it.

I wish the FSM gave more detail about what specifically causes the code (not the CAUSE, rather, the thing that the ECU reads to know there is a problem).

If it's reading it based on engine RPM response, or by return voltage from the IACV, or what exactly. I think it might be based on RPM response, and if so, that explains why it's so hard to fix this damn code, because it requires every single component in the car to be perfect. even the slightest Vac leak would pop a code., or a fouled spark plug, bad cats, etc.

i dunno, I don't care a lot, I've had my coolant bypassed for a long time and the car runs great, so i don't plan on screwing with this again unless I still have the car when it's time to do another Etest, at which point I'll have to figure something out.

I wonder if the ECU can be bad without any other symptoms other than the code? Maybe mine is bad from when it originally popped the code before I ever owned it and did the bypass?

Pilm

Good find and an interesting solution, the extra $90 is a bit much (almost the price of a new IACV) however for peace of mind it may be worthwhile insurance for some. I know some folks installed fuses to protect the ECU, and I considered doing the same, but then I figured it took 11 years for my original IACV to fail, so if the new one lasts anywhere near that long, it'll fail long after I've gotten rid of the car! BTW, the website you linked describes the failure mechanism more specifically:They don't say anything about coolant causing damage to the magnet wire urethane coating, instead it sounds like it's just a time and temperature thing (and maybe car vibrations) that finally causes the insulation to wear down enough so the wire windings short. This kind of seems to make sense with what we both saw, neither of us saw any evidence of a coolant leak, so perhaps it's not really the main culprit. Anyway, if time and temp are the main cause of failure, that would seem to further indicate you may have just gotten a bad coil from Autozone since wearing of the coating requires a fair amount of time. As you lamented, it's a pity the part wasn't measured before you first used it to know for sure, but at least you know the one you have now is good, so if the 2nd one were to fail you'd know for sure something else is causing the thing to fail. Hope the idle relearn goes well today, sounds like your idle is high and the relearn will hopefully solve that.

Pilm

I can't remember for sure but it seems I read in one of the old threads that if you only replace the IACV, but don't fix the ECU, then the bad ECU could or would damage the new IACV. If this is true, then there would be the possibility your ECU wasn't repaired successfully the first time and might have damaged your first IACV.

That said, I have a bit of trouble believing a bad ECU could damage a good IACV, b/c as far as I know the IACV can handle full current out of the STA509A mosfet, in other words, the ECU shouldn't be able to overdrive the IACV and cause failure. In fact, if the ECU did overdrive the IACV, I would expect it to fuse open the coil winding, not cause a short.

Anyway, I suppose if the ECU repair shop covered your 2nd repair for FREE under warranty, then I wouldn't want to break the tamper stickers either just in case it fails again (on the other hand, if they did make you pay for the 2nd repair, then the warranty is crap and there's no reason not to have a look inside).

TunerMaxima3000

iTrader: (4)

Wow good find! I have no problem believing that could be the cause

TunerMaxima3000

iTrader: (4)

More and more, I wonder if some of these issues are caused by bad wiring harnesses.
If the physical wires are bad and shorting from the ECM, you can replace a million IAC's and ECM's and still burn out the ECU.

Pilm

That quote from the ECU repair place was only talking about the wire used in the IACV itself, they use magnet wire with urethane insulation for the 4 internal coils. One thing I wanted to do with my old IACV was to examine the coils to see exactly what was going on, but there was no easy way to do that so I tossed it.

As far as wires between ECU and IACV, I believe the OP said he checked them for opens/shorts, so that shouldn't be his problem, but for others where the repair doesn't seem to work it could be.

TunerMaxima3000

iTrader: (4)

When wiring harnesses short they rarely do it constantly in my experience, they are almost always intermittent, which makes testing for a short very difficult

shaks

iTrader: (15)

you should check the ECU (open it up). my "new" ecu worked for around 5 days with IACV that tested good on tests mentioned in the FSM. After that it burnt. Maybe for yours it just took a bit longer than others? I did not do a bypass and it keeps idling a bit higher - around 900 in the winter, but at 1100 in summer (weird...) Also, sometimes I would have to hold the gas pedal for minute or two keep the car not dying. I don't get the standard idling when car is at the higher RPM when it's cold, but comes down after she's warm. I don't have a bypass.

I'm not fixing my issue, car is being sold with it and buyer knows about it. I'm including the new IACV in a deal though.

Tuner, I hope you will do something with the issue and try to document it for us as well. )

TunerMaxima3000

iTrader: (4)

Eventually I will have to, and ilk be sure to post about it.

I have a fairlynew evap code and wonder if it could be a vac leak causing issues, something I need to check soon

shaks

iTrader: (15)

Let me know if you need any readings from the car without the code. My new one doesn't come with SES light mod

ManualMaxima

iTrader: (10)

This explanation of the fail mode for the IACV is the best explanation that agrees with my experiences and opinion. This is a very good point, and one that should be tested for. I thought of this during running my wire checks, since we had 2 sets of hands I did all the testing with the multi-meter while the other guy tugged and shook the electrical wire bundles some , its not fool proof but gave me a better sense that all was ok in the wiring department.


Finally, I sadly didn't do squat on the car today. Had to work late, then I had to do a last minute valentines shuffle to find a gift for my girl (yep it's that unmanly day of the year again tomorrow) . I don't feel like dealing with it tonight and going to take a night off...

olypopper

ManualMax, any update on your car? My 01 is down with similar issues. I'm waiting for my ecu to com back and am installing an oem iacv so I'm very interested in your outcome. Thanks.

defiance

iTrader: (1)

Quick question: What do you guys use to bypass the coolant hoses that go to the IACV ?

ManualMaxima

iTrader: (10)

I'll have a result tomorrow, I had to put the fix on hold after having to work some SERIOUS hours these last few days unfortunately (early mornings/home real late). If you have any questions please don't hesitate, this whole thing has been such a headache that I'm eager to help anyone out...

TunerMaxima3000

iTrader: (4)

A barbed union the same size as the coolant hoses, can't remember if it's 5/16" or 3/8", probably 3/8"

And hose clamps to suit the need.

defiance

iTrader: (1)

Thanks for the tip Tuner, are you still running without your IACV plugged in ?
Cause im wondering how cold starts would work without the IACV...

ManualMaxima

iTrader: (10)

Well returned to work on car tonight. Ran her without the IACV connected till she was good and warm. While hot I re-connected the IACV harness, cleared codes, and Idle re-learn attempted, the max wouldn't drop below 1000rpm's and p0505 still coming up. Re-learn procedure run through a couple times for good measure, same result! The sh__ty mystery continues!!!

TunerMaxima3000

iTrader: (4)

My iacv is connected, just the coolant is bypassed. Has been for 2 Canadian winters without a single problem or hiccup in the idle.

Pilm

If you add a 2 mil shim on the throttle stop does idle remain exactly the same or does it increase? It if increases then your TPS is not set correctly.

It's also possible your car isn't accepting idle relearn. I've read others who tried repeatedly but it just wouldn't take and the idle remained high. This *may* be your issue, but it's just a guess.

Also, I don't know the answer, but if your car doesn't accept the idle relearn and your idle stays high, will that itself trigger P0505? In other words, could the fresh P0505 be simply the result of the idle relearn not taking?

Another question, when you replaced the IACV, did you verify your throttle plate fully closed and wasn't stuck partially open?

olypopper

I pulled the IACV off my car this am and found anti-freeze had leaked completely through the electrical connector AND into the intake manifold. Has anyone had an issue caused by water ingestion into the engine?

TunerMaxima3000

iTrader: (4)

Bypass this stupid ****ing Nissan system.

olypopper

That's first! I've already bypassed it with a hose I made and am just waiting on the new valve and ECU to show up.

olypopper

ManualMax, have you looked any deeper yet?

ManualMaxima

iTrader: (10)

Thx for the reply, and sorry everyone for not updating recently, I've been crazy busy and haven't even touched the car till tonight. I'll have to try your diagnosis procedure for closed throttle switch. You asked, "Is it possible that the idle re-learn didn't take?" and "the fresh p0505 is a result of the idle relearn not taking"= Defiantly!!! If that's the case though I don't know what else to do to make it accept relearn. I've followed instructions step by step multiple times. Don't know what I could do different to make it work.

As a note: I have run the relearn a few times where p0505 comes up during the process thus invalidating the procedure (usually during the 30sec idle run right before you disconnect the tps sensor. But I've also successfully done the procedure many times right before the p0505 code popped on my scanner. ~confused~

The fsm only mentions p0505 indicating only that the IACV-AAC valve is not functioning correctly,which confuses me because something else has to be going on. Also, why do other ECM rebuild companies require the TPS to be changed as well? Is there an answer to this other than taking it at face value?

TunerMaxima3000

iTrader: (4)

I can't do a manual one on my car either, I'm probably going to be stuck going to the dealer for it i guess

Pilm

The ultimate problem is the system isn't able to get target idle, but the only culprit isn't just a defective IACV, it could be your ECU isn't controlling a good IACV correctly. For example, if one of the four mosfets in the ECU STA509A chip was dead, then the IACV motor wouldn't be driven to move the pindle to change air flow and idle would remain out of spec. I guess the other thing is you are still using an aftermarket IACV, not a Nissan OEM part, if so, it's possible this is screwing you up for whatever reason. That was one reason I went with an OEM Nissan IACV, didn't want to screw with the possibility of getting a part that seemed good but for whatever reason wouldn't make the system happy.

noahrexion

In regards to the post above - I truly wonder what Nissan's requirement is of parts distributors now. Obviously these are (IACV's and thousands of other parts) are still being manufactured - and I just wonder if the tolerance spec that Nissan mandates of these OEM parts suppliers is always 100% throughout the years.

I see some folks having luck with aftermarket (most not) but obviously we also see folks having issues with OEM, or possible issues. On of the most common practices I see with all parts replaced, and the IACV is just so common that it almost tops the list next to MAFs and coils, is that once someone installs a NEW OEM part they almost always look elsewhere if they continue to see undesirable conditions.

Tuner: would you consider buying a new OEM IACV? Or is the basic ohm test on your "tester" just satisfactory to you? Obviously dealer techs have access to this type of diagnostic (trying another sensor if they wanted); it doesn't cost em' anything.