Kaane

I had a bad IACV motor code, I replaced it, found out my ecu was shorted out. Got a new ecu, took it to the dealer to recode keys, it started smoking 2 seconds after getting power. I open it up and it's burned exactly in the same spot.

So now WTF do I do? I seems the harness has a short in there, but now my new IACV could be busted. New harness is out of the question since it costs 2 arms and 2 legs. Anyone fix a short like this before? Any idea where it normally would short out?

This is on a 2001 I30.

Kaane

i checked for shorts and continuity on the harness and can't find any issues. IACV has 22ohm's between coils. So why the hell would the ecu fry? What else could cause this?

Matt93SE

iTrader: (44)

Where is the ECU shorting out? It may be something other than the IACV that's causing the problem...

Done anything else under the hood or dash recently?

Kaane

I have a check engine light for the IACV valve and it doesnt idle well at all, so i am pretty sure it's related. Nothing else electrical has been replaced recently.

Here is a picture of the damage.

Unklejoe

iTrader: (6)

I am 99% sure that there is a short somewhere.

You checked every possible combination of wires on the ecu harness for a short?

It appears that the transistor simply got too hot due to the extreme current flow from the short, and it exploded.

The STA509A at the bottom left of the screen is a power mosfet array. It is basically 4 mosfets in one package.

It is used to take small signals from the ecu processor and use them to manipulate higher voltages to actuate something in the car. They can be used to control the coils, injectors, or anything else that is controlled by the ecu.

I'm not exactly sure what the NEC chip is in the middle of the picture though.

Both of the chips that exploded are sort of near the 6 green capacitors. This makes me think that they have something to do with the coils or injectors, or anything else that there is 6 of.

I hope this helped.

Kaane

I traced the path from the STA509 chip and it goes to the IAVC motor pin on the ecu, so it's definitely the same circuit.

There are 6 wires that go into the IAVC motor, 2 are power and 4 go into the ECU. I tested for continuity from the connector to the ECU, also tested for shorts between the wires and also for shorts to power and shorts to ground. Didn't find anything

Only thing i can think of the short happens when there is current going through the wires. I started taking the wire loom as far as I can see to look for damage, but so far no luck.

nsnrider

iTrader: (59)

also make sure the pins in the plastic connectors are straight and not bent or damaged and clean without any debris in there, both at the ecu and at the IACV. Are you sure your "NEW" IACV is not shorting out? Any blown fuses? Any other burned electrical parts besides the ECU? Did your old ECU get damaged the same exact way?

Drockb418

iTrader: (10)

any wire that looks like it was melting? sounds like a power wire being grounded out.

Kaane

No wires look burned, but i have not removed the entire harness out of the car yet, so it is possible there is some dmg where i cannot see it. Old ECU got burned exactly in the same spot. It is obvious that there is a short and too much current goes through the chip and it melts, but i can't find it and the harness test so far dont show any.

I tested the new IACV and it reads 22ohm between the terminals just like the factory manual specifies.

Kaane

Started ripping the harness out of the car Got all the connectors under the dash disconnected. What a pain in the ***.

Can the harness be pulled through into the engine bay? or will the ecu plug not fit through the firewall?

odessa_mama_13

All,

I am sorry for jumping on this thread, but I am new to this forum and can't post my own thread, yet. I just experienced a problem that I am trying to get some help so that I can better understand it.

I have 2001 Maxima SE 20th Anniversary (5 speed) with ~135K miles. For the most part it has been a smooth ride, with one exception and that is emissions.
- 55K I got a P0420 (Catalyst System Efficiency Below Threshold Bank 1). I took it to the dealer and they re-programmed my ECU. I was told that there was a re-call on my car and the emissions thresholds had to be updated. Problem solved.
- 110K I got a P0430 (Catalyst System Efficiency Below Threshold Bank 2). First mechanic wanted to replace my catalytic converter. Second opinion resulted in just replacing one of four oxygen sensors. I didn't capture which one it was, but I am guessing it's the one that controls Bank 2.
- 113K I got stranded on the road once because I lost power. After a tow back to my house, the car started fine the next day. I took it to a mechanic and he tested electrical system, but could not find anything wrong. So continued driving until I got stranded again and this time it was clearly an alternator.
- 115K another Oxygen Sensor (13374).
- 124K power steering high pressure hose.

So here is the fun part. I get another P0430. Two different mechanics tell me that I need a new catalytic converter and Oxygen Senor(s). Day before I take in for repair, I decide to reset my computer by unplugging the battery for about 15 minutes. Plug it back and Check Engine light is still on. Oh well, I take it to the mechanic. He calls me couple of hours later to tell me that the code is no longer P0430, but instead it points to an Oxygen Sensor that controls Bank 2. I told him that I tried resetting the codes with the battery and maybe it'll take some time for P0430 to come back. So we decide to just do O2 sensor for now. I get that done and while driving home from the mechanic (~ 5 miles) my car stalls. I tried starting it, but it just won't hold the idle. I also smelled an electrical fire inside the car. I towed it back to the mechanic and he told me that my Idle Air Control (IAC) valve shorted and fried my ECM.

Couple of questions here:

- Is there any way a new O2 could short my IAC or this just a freaky coincidence?
- Why do I seem to have electrical problem around the same time my O2 sensors are being replaced?
- How common are these problem in 5th Generation?

I love driving this car, but I am almost at the end of the road here. Please help!!!

klemenz

Hmm. My car has similar problems. The p0430 is a common problem

My car has the p0430 code and my alternator is also bad. Been fine for about 4000 miles though, just killed a battery.

NisTech

it does fit through the firewall. that's how u replace a harness
i think there was a tsb for 2000 or so max with harness getting shorted around top of engine by the injector area bank 1
also what i would do if i would print the section with iacv since you narowed it down to that. follow it throughly and check for power at terminals of ecu and ground.
there is a chance that before the old ecm fried it may have overheated the wires too and damage insulation. Then when you plug in the new ECM completes the circuit since ECM controls ground so instead of iacv being the load it becomes the shortest path which is your harness shorted out. Since harness is expensive and you already have it out you could start opening it up with exacto knife very carefully after u test like i said everything in the manual section and check ECM harness pins as per section, and then if IACV tests fine start opening up carefully harness and look for any damage.
Continuity may be there (hope u do that with power disconnected but u will get continuity if 2 wires melted together. That only checks for open wires.

20thAnn

Haven't pored over this thread, but have you checked into the active motor mount issues these Maximas have? It's hard to believe, but Nissan's attempts to make your engine purr quietly might have caused a major ECM malfunction. I just BARELY got mine replaced under the 80/8 warranty. They unhooked active engine mounts, replaced IACV (on my dime), then later found out the ECM was fried and replaced it.

njmaxseltd

iTrader: (19)

I think you're wasting time with the wiring harness, they don't just short out. Doesn't happen. You need to look closely at the devices, IACV ect. Especially areas where you just did some work. Check plugs, check replacement parts, they can be defective right out of the box. Check coil packs, check injectors - a device is shorted out. Strange you didn't blow a fuse first.....

I had a similar situation with my 4th gen blowing a ECM fuse, to the point I couldn't get the car to run anymore. Turned out to be a bad coil pack, although a mechanic told me it was my wiring harness. I told him no way, that just doesn't happen and took the car back. Took me two days to find the culprit.

Good luck with your search!

Colonel

Believe it or not, I believe the new guy has point. Who woulda thunk it?

Kaane

Harness has no shorts, I removed the whole thing and checked it. I did ran into something interesting, there is a company that fixes these ecu's and they claim that a bad Throttle position sensor can cause the ecu to get fried. I asked them how it's possible but they didn't answer. They also said that running a new IACV with fried ecu will just damage the IACV again. I tested the IACV valve and i am getting around 24-25ohm between the terminals. The manual says 22ohm's, could the IACV be fried again?

Kaane

wow the engine mount thing could be it!! I just opened the fried ecu again and tested continuity from the pins of the fried chip to the ecu pin that goes to the engine mount, and one of them has a continuity!

2K2Beast

TO EVERYONE WHO HAS HAD A SHORTED ECU IN CONJUNCTION WITH SOME SORT OF IACV PROBLEM:

My friend 1phatmax had the same issue, and both (2!!!) times he bought an ecu it was from a dealer who should have known this.......if you have an automatic then you have electrical motor mounts.

Your motor mounts are MOST likely gone bad, shorting out your IACV and/or ECU....

only if someone had sued Nissan would have put out a recall or TSB for this isssue........


EDIT: Its most likely your Front/Back mounts and not the Right/Left mounts

Kaane

I checked the motor mounts today, YEP! one is 100% shorted, I get battery voltage on all 3 pins of the connector, even though only 1 should have power. What a pain in the ***.

unrealii

iTrader: (8)

Anyone drive around with the motor mounts disconnected? I'd rather deal with more nvh than buy a new ecu if this bug hits me.

Kaane

ok to finish my story, I got my ecu repaired for $349. Unplugged my motor mounts, bought manual versions. Fired it up today, idles great, no check engine light and no smoking from the ecu.

So If you ever have bad idle check these things.

1. Open ECU and look for burned chips
2. Test IACV motor for shorts
3. Check Motor mounts for shorts

Check Harness only if the other 3 test fine.

nakis

Good to hear that you fixed and thanks for sharing. I am just begining to dig in.

The ECU is fried from the IAC motor going bad.

I have ordered the STA509A IC and will solder in the new chip and a few wires in place of the burned out circuits.

I will check the harness for shorts.

I will keep the IAC plug disconnected, and run the car a few days before I order a new IAC motor.

I am working on a manual so they are no Electric motor mounts.

Thanks again.

Kaane

One more thing to add. In the picture of the damage, the ST509A Chip is for the idle, if the chip on top is burned then it is the motor mounts.

Love_00_Max

How does one determine the auto mounts are on their way out? I have 160K on the original mounts, though they are strong one never knows when these things can fail and land the owner with a large bill.

Love_00_Max

BTW, this thread should definetly added to stickes.. Great thread indeed...

Thanks Kaane and others for their valuable inputs.

nakis

2001 Maxima with a Manual Trans
The IACV ohmed out ok, could be the IACV seized up and a high amp draw fried the circuit?

Kaane

yep that ecu idle chip is toast. Make sure the IACV has no continuity between the top and bottom sets of pins. Sometimes it can ohm out ok but still have a short.

nakis

I traced out the burned circuits,
ECU pin 6 to STA509A pin 9
ECU pin 8 to STA509A pin 3
ECU pin 7 to STA509A pin 7
ECU pin 17 to STA509A pin 5




I soldered in the new chip and ran wires to the correct pins.







I tested my wiring harness for continuity and shorts, which tested out good.

I ohmed out the IACV and for shorts and it checks out good,
but I will not connect it to the harness until I replace with
a new IACV. The IACV is leaking antifreeze and that is probably
why it fried up the ECU.

I did connect a logic probe to the IACV connector and the circuits
are oscillating a signal, I guess the only real test is when the new
IACV is installed.

I will let you people know how it turns out.

bgod

So do all the manual transmission mounts interchange with the auto transmission mounts?

I'm assuming at least the transmission side mount would be different?

Is it a simple drop in procedure and disconnecting the lines to the mounts?

nakis

I am trying to thoroughly think this IACV burning up the ECU problem.

I have two theories so far, Coolant shorting out the IACV motor
and a second one which I am more leaning to what causes the failure.

The IACV has Thermo-valve in its body that is a mechanical valve that
is open when cold to allow more air to bypass the throttle plate to allow a
higher rpm idle and when the coolant heats up it will gradually close the
thermo-valve to lower the idle.

If the thermo-valve is stuck open with the engine warmed up, the IACV
circuit will try to lower the idle rpm and the IACV motor will bottom
out on the valve seat and it will keep trying to shut the valve trying to
lower the idle rpm to compensate for the stuck open thermo-valve, which
will causes a high amp draw and take out the weakest links in that circuit
which is the ECU.

Same problem could happen if the TPS is bad or not adjusted correctly,
and the computer does not know the throttle plate is open and there is no
need for the idle to be adjusted.

I would be interested in any comments.

Kaane

I came to the exact same conclusion. I have an intake leak either in the manifold or the throttle body, the extra air is being bypassed causing high idle condition, the ecu tries to correct it via IACV and over time burns the chip out. Both of my IACV valves tested good, and i am using one right now. Using DATASCAN software i can manually enter idle correction and it goes up and down, it just can't get any lower then 900. I can manually move the throttle body mechanical stop a bit lower and i can get it to idle at 750, but now the throttle sticks a bit.

I can hear a bit of a sucking noise when i step on the accelerator coming from the motor. I am just wondering where the leak could be at.

nakis

Thanks for the heads up on the Datascan software. I have downloaded the Nissan datascan 1.52 and I will see if it will work with my ODB II cable.

I wish I can suggest something, but I do not know for sure, only thing I can state is what I am trying.

I have disconnect the connector to the IACV and manually set the idle by taking the motor out of the housing and ratcheting/turning the valve clockwise to counterclockwise and pulling the valve out ( which will lower the rpm) or pushing down on the valve while ratcheting to raise the rpm. I measure the gap between the valve and the motors base and then I put everything back together to check the Idle speed. I went through the whole process multiply times, until the Idle was set at 700 rpm.

Next, thing I am going to do is take the thermo-valve apart for inspection and cleaning.
I will then test the IACV with its motor off, by placing in a bail of cold and then hot water to see if valve is closing.

I know a new IACV and a new TPS adjusted correctly should fix everything if my ECU repair was done correctly, but this is not my vehicle, so I will feel bad replacing expensive components, just for them all to get damaged again. .

Kaane

I replaced the IACV with a new one before I replaced the ecu, so i am hoping that thermovalve should be fine. I am going to take the intake manifold apart and look for leaks and replace the main upper intake gasket, I already replaced all the TB gaskets, does anyone know if there are any gaskets inside the TB that can be replaced? I know in some other cars you can have leaks through the shaft seals.

Kaane

The software is actually called NDSII it is the obd 2 version. The regular datascan 1.52 will not work.

you can download the NDSII here.

http://www.blazt.biz/products/engine_software.php

nakis

Thanks.

Did you try spraying the intake manifold with 2 + 2 Carb cleaner or starting fluid to see if you can find the leak? A leak will suck in the flammable solvent and raise the idle.

Kaane

tried it and it didnt do much other then make my car smell like gasoline. I am guessing the leak is in a spot i can't reach.

nakis

After testing the IACV, I decide to see if the motor would work, well the IACV blew out the chip again. Oh well, I just experienced the definition of insanity.

I ordered the new IACV and a STA509A chip and this time I installed some fuses on the circuits.


I have made some notes of where the rest of the circuits will trace out to, just if anyone needs for reference, I had to repair the circuit board for pin 2 and I then made sure the circuit had continuity and then tested for shorts.

The car runs and idles great now, everything is in spec Idle at 638 rpm and the Timing at 15 BTDC, and the IACV will adjust the idle for loads like the PS and AC.

The problem it keeps throwing out code P0505, any time I press the gas pedal over 1500 rpm, it will generate the code.

The freeze frame data shows the RPM at 1538 rpm.

I adjusted and tested the TPS and it tests out ok, The ECU rebuilders recommend replacing the TPS, so I think I will just replace the TPS to see what happens.

I have done the RESET THROTTLE POSITION SENSOR IDLE POSITION MEMORY and the IDLE AIR VOLUME LEARNING.

I do hear hissing sound, but I can not find a vacuum leak.

If anyone has any suggestions and could help, it would be appreciated.

Thanks

Donny G

I got to hand it to you, You saw this trough with major resolve Congratualtions. You're very talented to have had the nads and the brains(And a strong back you must bend like gumby) to get that haraness out and go over everything the way you did, mad props WTG man

anyone seen the powerprobe tool (brings power and ground to any cirscuit) and short locator kit been meaning to buy one Saw a guy using one on His E36 beemer great tool......... Shorting motor mounts unreal

denice25

pretty bad.... check your wiring or fuse..