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What fries an ECU on a 2002 3.5L?? No IACV, right?
TITLE EDIT: Please see most recent posts to find where I'm at on this now.
Hi everyone
Our '02 bone-stock I35 w/113k on the clock had a weird burnt smell yesterday. I got it to the side of the road to look things over, but the smell wasn't super-strong. I googled it and was unaware the motor mounts were an issue with the VQ35s as well. I immediately disconnected them and drove it home. This car has no IACV, so I didn't bother looping it out of the system today.
I just pulled the ECU and got these pictures. This ECU has "FQ" on top. Part number looks to be A56-T69 ZP8. NOTE: The bottom seems completely fine except a minor spot around the 5th pin in that chip. No tracers on bottom are burnt/black. Just that one on top that runs under those green chips.
The car seems to run perfectly fine except some slight hesitation/surging that I think is more related to 1 non-OEM coil I had to swap in a few months ago and then forgot to track down a matching set of 6. (Wife's car and is barely driven)
Does anyone know what system this chip is responsible for? Is it OK to continue driving if this thing just controls the motor mounts?
The weird thing is that there are NO CODES?!?!
Last edited by mydecember1985; 07-27-2021 at 05:25 PM.
Thanks, but please explain. Other than knowing to unplug the motor mounts and looping out the IACV, I never had to read into this on my old '00.
What is a ST509 and what is it responsible for? I know ECU failures are almost always because of a DIFFERENT component failing, so I need to address that before I get this repaired and it fries again.
Thanks for any pointers.
And who does good work nowadays? Most of the links I found for repair services are no longer active.
Thanks, but please explain. Other than knowing to unplug the motor mounts and looping out the IACV, I never had to read into this on my old '00.
What is a ST509 and what is it responsible for? I know ECU failures are almost always because of a DIFFERENT component failing, so I need to address that before I get this repaired and it fries again.
Thanks for any pointers.
And who does good work nowadays? Most of the links I found for repair services are no longer active.
Your motor mounts (or wires to them) are fried.
Leave them unplugged and keep chugging along.
Hell even replace them with some aftermarket mounts. There's 0 need to have electronic mounts in a vehicle this old.
I can do all of the work but I'm located in Houston, TX
Does anyone have contact info for "The_Fixer" here in Tampa? Hoping to see what his turnaround time is before I ship it tomorrow.
After 4-5 months of just being down on power a few percent, we're finally getting to the point where it's stalling and significantly down on power. Code P0172 Bank 1 Too Rich is now being thrown. For 3-4 years, cylinder 1 has had low compression of 130PSI on startup because of a bad ring. Once it reaches full operating temp, it's back to 195 PSI. Never threw a code all these years until this ECU thing happened. I have been monitoring oil dilution by sending off oil samples every once in a while with concerns of blow-by until the ring seats fully. Seems to not be a concern. We are sending the ECU to http://www.foreignecurepair.com/ for repair.
I'll update if it's a simple fix when plugging it back in. Turnaround will probably be about a full week.
So the ECU made it to Foreign ECU repair yesterday. They repaired it and are sending it back soon. They recommend I replace the IACV, but our car doesn't have an IACV. See picture. It's all one big piece of the throttle body. Is this part known to cause ECU failures? The motor mounts are still unplugged. Anything else I should replace?
Replaced Throttle body to be safe. Motor mounts are left unplugged. Went to start car to get it warm and complete relearn. Car ran like absolute hot garbage! I was freaking out. The exhaust was smoking a bit (never has before) and stunk of unburnt fuel. I couldn't even get it to maintain an idle long enough to warm it up and do the relearn. If I did keep revving it to warm it up, I was worried the insane amount of fuel dumping into the system was going to ruin the car's already-fragile cats.
Since MAF has a lot to do with A/F ratio, I went to grab a Duralast replacement. The closest Denso/Hitachi was 4 hours round trip. $110 and it fixed the rich condition. I was able to warm the engine and relearn idle. Total cost: $250 ECU fix, $130 throttle body, $110 MAF. $490 total I'm really wondering if the MAF was the whole problem with the hesitation and the ECU was completely unaffected because it drove fine for a while the ECU burned up back in February-ish and I unplugged the mounts.
I also have a spare throttle body now since it was doubtful that caused the failure.
P0650 Malfunction Indicator Lamp (MIL) Control Circuit Malfunction
I haven't dug around to see if it's a fuse issue or a wiring issue. Possibly the ECU itself?
We've had no other problems with the car in the past except a camshaft sensor and an alternator. Easy stuff for 5+ years of ownership.
02-27-2021, 04:14 PM
replacement. The closest Denso/Hitachi was 4 hours round trip. $110 and it fixed the rich condition. I was able to warm the engine and relearn idle. Total cost: $250 ECU fix, $130 throttle body, $110 MAF. $490 total 
I'm really wondering if the MAF was the whole problem with the hesitation and the ECU was completely unaffected because it drove fine for a while the ECU burned up back in February-ish and I unplugged the mounts.