Did you read the thread above? What is missing?

 

Still have the p0505 after replacing the TPS, IACV and ECM repaired. Any ideas? Maybe CTS? Anyway I can start testing these components?

Thanks guys!

 

And now after all this time it's my turn.

It looks like my IAC is fried on posts 4,5,6 in terms of having a short, and no resistance between 4&5 and 5&6. But 1&2, and 2&3 have about 24 ohms.

Ok so, I FINALLY got my ECU out, and it looks like there are (2) STA509A chips. I thought Pilm mentioned 4 of them. I also noted that the chips looked good, and the traces were clean. So I don't know if I should replace them as a precautionary measure. Once removed I can check the old IC's, but at that point, why put the old ones back in? I may as well replace them.

It's 2k SE. Is it just possible it's a different core? I plan on buying 2 chips and going to a friends to have him do the work. I could, but seeing it's my ECU id rather someone else do it.

 

Be careful not all 509/508's are the same

 

If you flip the ECU upside down switch the multi-meter to Mega ohm slot check from IACV pin on ECU I/O where it comes through the circuit board to chips for continuity. You should get "something like" a .599 - kilo ohm reading. carefully follow the IACV circuit through the board checking all points between with the ohms slots.
right?
SOme chips you might not get any continuity on certain circuits. You may need to switch to higher mega ohms slot or lower ohms slot. I wasn't getting any numbers through the back-up power circuit chip on the 2M slot. I only have 2M on mine.

 

I have acess to ecu's if anyone needs one.

 

15 years later there are lots of them available!
Why you would replace such an expensive part at the customers expense "just to be sure" is Bizarre ! It's like cornhilio posted of its not burnt it's probably fine
The only other issue could be where the pins solder to the circuit board

 

I'll have to save this thread for my tech friend to read. The problem is that I have no clue which pin is from the IACV. Maybe it's in my Haynes book.

 

That's a hell of a thing to say now that I ordered http://www.ebay.com/itm/191957565920

I hope these kids are good. I'd hate to see different specs on the same chip.

 

And just a quick update. I said "no resistance" between two sets of pins. It was actually about a 2 OHM load. Maybe not enough to fry the chip, or maybe just not enough to do external damage.

 

If you had only 2 ohms when measuring the IACV, it is bad. 2 ohms will keep you from frying the STA509A chip, but it will probably short out in time. A good IACV will have 22 ohms. One or two ohms off of spec wouldn't be of concern, but you only have about 10% of specification.

 

Yeah, I'm hoping the 2 Ohm load is keeping it from being a dead short and blowing the 509's. Though my friend did a quick calculation and said, "well that's 6 amps of power, it MIGHT be fried."

I ordered those two chips and we may replace them as a precautionary measure.

In the meantime, I have disconnected the harness from the IAC, as I don't want it possibly making matters worse. You know, actually frying a trace...

 

Well, I replaced the IAC, but can't get to the MOSFET's for a few days. What I've noticed is that the engine will not take the Idle Reset, and I'm running about 1500 RPMs, and it fluctuates. I'm uncertain if that means one of the chips is bad, or if it could be something else; as it is also still throwing the P0505 code as well.

Also the IAC can be separated from the coolant housing. Once done, I noticed a little coolant inside, but not a lot. Should it have any coolant inside at all?

 

There should not be any coolant inside. That leak is why so many people have had their ECUs burn up those chips because the ethylene glycol eats through the IACV stepper motor winding insulation and causes the motor to short, which causes the STA chips to burn up..

The P0505 code is saying that the IACV does not respond to commands. It could be either a bad IACV or a bad ECU. If the STA chip has shorted, it can not "tell" the IACV to do something and you will get the P0505. When you have a non working IACV or ECU, the engine idle will be all over the place.

 

Thanks. I'll replace the entire coolant chamber. Maybe it has a pinhole leak in it.

I am going I try and trace which one of the two MOSFET's I need to change on the board. Hopefully I will get that in the next few days.

 

Bypass the coolant around the iacv

 

Actually a guy at work mentioned that. I just don't have a bypass tube readily available. And considering this lasted 16-17 years, I figured replacing the gasket and chamber should last a long time.

I wonder how engine power would be without the hot water heating up the throttle body.

 

you can buy hose at the auto parts store. and while i tend to agree with you that a new one should outlast the car, bypass is an easy mod to ensure that.

many members (even those in cold climates) have reported negligible change from doing the bypass

 

I guess I can get a foot of hose and cut off what I need. As others have done it, I don't need to worry about the hose pinching, and it would make putting the throttle body back on much easier. Hell, as it is I am having a hard time getting one of the hoses OFF so I can remove the TB. I need to start again in daylight.

 

I thought you replaced the IACV. If you have a new IACV that is leaking, return it for a good one. If you are still using the old IACV with only 2 ohms resistance, you have to replace it. You will not be able to salvage it.

I can understand you wanting to wait until you get the STA chips replaced, but I think you are driving yourself crazy in the meantime. Put on a new IACV, do the coolant bypass or not (it won't matter, you won't have the car 15 years from now) and live with the erratic idle until you get the STA chips replaced.

 

It's so much easier to remove the entire throttle to seal the IACV.
try your local Nissan Dealer #16076M ---> $3.40

 

Dennis, I originally replaced just the IAC itself, but not the entire unit, as I did not want to pull the entire throttle body. I finally pulled the TB and went to replace the entire unit, but installed it with the coolant lines intact. Unfortunate I did. Ithave Maximatech's coolant line part number before I installed everything. The hoses at Autozone weren't long enough to shape into a bypass...

I believe the ECU has 2 STA chips, so I may post a pic to see if anyone knows which it is, instead of fooling excess desoldering and such to the board.

 

i used half the hose i bought to do the bypass, i think i got it at advance. since you ran the new iac without replacing at least the gasket, the coolant leak would have still been present so it's possible you could have damaged the new one also

and don't listen to maximatech

 

Parts stores sell hose by the foot off a roll. You should be able to get a piece as long as you want. No reason to go to the dealer for a piece of hose. You can just leave the connections on the TB open.

I agree 100%. Especially with your last statement.

 

Just for clarification. I went ahead and replaced the entire IAC, as the coolant should not have been in there. The gasket was also replaced.

As for the bypass, I did not do it because I honestly have no idea if coolant hose is different than fuel line, and all Autozone has is fuel line by the foot.

 

Fuel line would have been fine. Since you replaced the gasket you should be fine either way though. If you ever have it apart for something else it may be worth doing.

 

Does anyone know which 508 chip it is? And yes, I ordered 509's dang it.

I am guessing it's the front one. Having a hard time getting continuity to find it for sure

 

None of the chips look like they are fried. You would definitely be able to tell that. But it could be bad without burning up.

There is one ic that looks questionable. There is a pair of chips roughly in the center of the photo. The left one of the pair, on its left end, looks a little different. It could just be the lighting. Is this a cellphone photo? It looks like it. Immaterial though.

Here are two photos of burned chips.

 

Wow that was easy enough to see the fried chip. My fluctuating RPMs is what's making me think the chip was damaged. I wish it was more clearly seen.

 

Didn't you say that a friend would solder the chip in for you? Is he a electronics tech or a good amateur? Hopefully he would know how to check the chips with an ohmmeter.

 

I am hoping he will be able to test the ICs in circuit. Sometimes They can be a little problematic, especially without schematics.

What concerns me more is the board repair. My skills go as far as Pac-Man arcade machines which have nice big traces. This work is getting very delicate, and I don't even think he has worked or something this small

 

For soldering on printed circuit boards like the ECU, you use a soldering iron that is no higher than 15 watts. The process is the same. But even with a low wattage soldering iron, you can still apply heat for too long a period of time, which will lift traces and destroy the ic.

for chip schematics, try these links. Look at the lower right corner.

http://html.alldatasheet.com/html-pd...1/STA508A.html

http://html.alldatasheet.com/html-pd...1/STA509A.html

 

Thanks for the soldering tip Dennis. I have two STA 508 chips on the board, so I tested the paired legs. Each pair measured in the mega ohm range, except for two pairs which measured in a kilo I'm range. So I know there is damage to the chip.

For now, the car is running great! After removing the entire throttlebody and scrubbing it clean, it is really performing well.

Thank you for all the help everyone.

 

I just did the bypass because of this potential frying ecu issue myself. I don't understand why some bother w/ linking the two hoses together w/ a nipple and hassle. I just got a foot or so of fuel line at autozone and cut it to fit. Works great. Makes pulling the TB in future a lot easier, too, as the line as slop in it for movement now.

So far so good w/ the bypass line.

 

I noticed the EGR has coolant going through it also.

I haven't really investigated that. But is it sealed away from the stepper motor or is it like the IACV. Both work in a similar way.

I may bypass both of them. But not if it isn't necessary.

 

Maybe I am misunderstanding what you asked, but the IACV stepper motor is not supposed to have coolant in it. The antifreeze getting in the actual motor is why the IACV fails, the antifreeze eats the insulation off the wires. This holds true for the EGR also. There should not be any coolant inside the actual motor.

Bypassing the IACV was a way to avoid the problem if you had one of the defective IACVs. But not all the IACVs were defective. If you still have the original IACV, it probably is not one of the defective ones. As has been mentioned in this thread, you can do it if you want as there is no real harm in doing it. But I have no way of knowing if your IACV will fail. This is a personal preference call on your end. If original, it is almost 20 years old and could fail because of old age. No one really knows what the lifespan is on this. The 4th gen Maximas have the IACV also and it is rather rare for one to be replaced.

As for the EGR, I don't remember anyone having a problem with the thing shorting out and burning up the ECU. I would say don't bother doing a bypass.

 

I was asking essentially ,is it possible to get coolant in the EGR stepper. Like the IACV.

I have never owned ,5th gen with this set up.

As for my IACV it buzzes with the key on loud.Getting the P0505 code.





I took pictures of the ECM.