Hey guys. New to Maxima.org but not to car forums in general. I'm mainly here to learn about Maximas, as I'm a part-time shadetree mechanic (as I'm sure alot of you are) and am trying to help my boss out with his daughter's car. It's a 2000 Maxima GLE, A/T, federal emissions, and I'm about 99% sure it doesn't have TC.

I've worked on this car several times in the past (brake issues, P/S hose, a few ignition coils, headlight socket burnt, etc.), but it seems we've encountered the dreaded engine mount/possible ECU failure

Last year, the front motor mount started buzzing, so after researching part costs, etc, we decided to take our chances and just unplug the suspect mount. About a week ago, my boss told me the car was having much the same issue it'd had once before w/ a dead ignition coil, and the SES light was on. Sure enough, another of the "front" ignition coils had gone south, so I replaced w/ a new one. I instructed him to have his daughter go have the codes cleared, as I didn't have my scan tool at the time, but she never got around to it. A few days later, she'd been out driving all over town one day, got home and the car wouldn't start. SO, I grabbed my scan tool and went to look at it. It would turn over fine, but never would fire up.

The SES light was off, and didn't even come on for the "bulb check" when you first turn the ign on. Plugged up my scan tool and it couldn't communicate w/ the computer. Checked all fuses/relays and all appear to be fine, so I started doing my homework. According to his daughter, the car ran perfectly fine right up to the point it wouldn't start (no idle issues, presumably). I removed the ECM and popped the top off, to find everything looks in order; no burnt circuitry, etc.

My question at this point is whether to suspect the ECM is shot, in spite of no apparent visible IACV/motor mount failure on the circuit board, as I've read is often the case, or if perhaps something else is suspect? I've spoken with all the local dealers' svc depts and all agree that they must have the vehicle to perform a diagnostic- that they won't just plug the ECM into the CONSULT II and tell me if it's functioning. I find this hard to believe, but that's the story I'm getting, and paying towing costs and dealer repair costs isn't really an option.

ANY suggestions are appreciated. New motor mount should arrive today, and I'll be replacing that since we know it's bad, even if it didn't cause this particular problem, but we'd like to determine if/why the ECM failed so I can further diagnose the problems, before paying for a new ECM & VATS reprogram, or have the unit rebuilt...

 

Well, after talking to a rebuilder who's actually located here in TN, only about an hour away, we've decided to send it to them, since they bench test all ECM's anyway before repairing them. I'll keep everyone here posted on the findings (although I'm sure you're all with me in your assumptions of what it'll turn out to be...)

 

No check engine light and a failure to communicate points right to the ECM unfortunately. I'd say check if it's getting power but it sounds like you already did that.

I guess it's too late now but if you had another max you could swap the ECM and test it that way.

 

Okay guys- back with another question. After speaking w/ the technician who worked on our ECM, he confirmed that there was a failure in the IACV circuitry. Prior to just blindly replacing the IACV/AAC, TPS, or other expensive OEM parts, I'd obviously like to test some things. My problem, though, is that most of the TSM tests require that you start the vehicle, which I'm afraid to attempt to do when I know there's some sort of problem which fried my ECM that has not yet been fixed...how have you guys gotten around this without blindly throwing more money at parts that may not be faulty?

I guess my next (most obvious) step should be to remove the IACV and test resistance/visually confirm that it's both functioning and not leaking coolant. I just don't want to start the car until I feel confident that the underlying issue has been resolved...

 

Something doesn't check for me here - if IACV driver chip in ECU was bad indeed then I'd expect it to burn some small conductors on ECU PCB so it would leave ECU without power which would explain the original set of problems. OTOH, you supposedly opened ECU and checked both sides of PCB and if the above had happened you'd find IACV chip burnt (literally) and some melted PCB conductors around. You never said you noticed so I really doubt IACV driver is the culprit. If you're any good with multimeter I'd recommend checking ECU power (5V) circuit since if that is dead the rest would behave like you described. In that case you will need to repair/replace ECU and leave the rest alone for now. If you can't communicate with ECU through scan tool then it's a waste of time to look elsewhere- solve this problem first.

 

When I removed the top cover, there was no visible damage to the STA driver chip as I'd seen in photos on here, so I didn't really probe any further (i.e. I didn't remove the bottom). IIRC I checked the voltage to the ECM @ the connection and it showed battery voltage with the ignition on. I'm about to go have a second look at some things right now, so I'll test that again and determine conclusively if the ECM is getting power, but I'm about 99% sure that it is.

Just to be clear, I've already had the ECM rebuilt. Now the question I'm dealing with is what caused the failure, so I can fix that before attempting to run the car and risk frying the ECM again.

I'll run the voltage and resistance tests on the IACV, possibly remove it to check and see if it's operating at all, leaking, etc, and do the coolant bypass mod. I'll keep you guys posted.

 

May be nothing is at fault - there were few rare occasions reported here when internal ECU power supply failed - the one which converts +12 V to the +5 V for the ECU chip and some others. BTW, STA driver is powered from +12V so when it goes it never affects +5 V circuit, just melts surrounding conductors on PCB.
Keep in mind that ECU uses several +12 V sources but only one is used to power the chip. I don't recall which one, unfortunately.
You probably can open ECU and see what was replaced yourself - it's hard to replace something without leaving any trace. This way you might have better idea what caused the failure.
You can also leave IACV connector disconnected and see if your rebuilt ECU is working - at least everything else should be working, it should communicate with the scan tool and you can even start the engine by opening throttle slightly with your foot.
I can recall only single case here when something else besides IACV driver inside ECU was causing drastic effects. In that case it was ignition coil driver and it kept frying up ignition coils which owner kept replacing. It also was doing it in quite spectacular way - smoke, bubbling plastic on the coil, etc. Fortunately, it's irrelevant to your case. IMO, if you leave IACV connector off nothing else will be able to damage ECU.

 

I had problems with my 2000 i30. It had misfire and all systems were fine. Pulled the ECU and it looked great. Later decided to replace it and the problem was gone. Even if the ECU looks good visually there could still be a problem. Take off the IACV and test it. If you just plug in the ECU nd try to start the car you will probably fry it again.

 

Well, I removed the IACV and inspected it. Visually I could not find anything wrong with it, but I know that doesn't count for much of anything. I tested the continuity readings were consistently 23. The FSM says "approx. 22", so that's kind of vague. Would 23 be within spec? I don't know. I didn't attempt to do any of the other tests (i.e., voltage test on the harness side, harness continuity, etc.) b/c the computer isn't yet plugged back in.

Also attempted to test continuity of the TPS and closed throttle position switches but wasn't satisfied with the results I was getting, plus I sidestepped the TSM by not running the car before testing anything.

I guess I should have just buttoned everything back up except for plugging in the IACV and seen if the car would start. Maybe then I'd be able to tell if the TPS was bad also. Good suggestion on opening the ECM, except that the rebuilder sealed it and I would void the warranty if I opened it. But I wouldn't really know what I was looking at regardless, so not much point in me doing that.

Basically at this point, although I'd like to be 200% confident it's the IACV or the TPS (or both), I feel inclined to just replace both, as the ECM rebuilder suggested, for a couple reasons. For one, the car's been down for weeks now and my boss is prepared to throw whatever other money at it he has to just to get it running again, so I'm kinda tired of scratching my head over stuff I don't fully understand. Secondly, since most people replace the IACV as preventative maintenance, and the rebuilder told me the ECM failure was related to the IACV circuitry, it just seems logical to me to replace it and do the coolant bypass to at least alleviate the possibility of it failing in that manner in the future. As for the TPS, I think we may just order it and wait to open/install it until after I've got the IACV in and the car (hopefully) running.

 

Max_5gen, I just re-read your post. So you're suggesting that possibly the only problem was the ECM itself?

 

Precisely- if you plug it back in and leave IACV disconnected (just in case) it is supposed to communicate with scan tool, control dashboard lights meaningfully, even allow you to start the engine, provided you would perform IACV job yourself by pressing gas pedal slightly. Cheap test and it doesn't involve replacing anything.
If it starts the car successfully then I'd take really hard look at IACV, If your problem persists I'd take the same look at the ECU re- builder as ECU is supposed to at least communicate with scan tool even if everything else fell apart.
BTW, my understanding is that when IACV fails one of its step motor windings gets short which leads to loss of inductance, not resistance so it is impossible to detect with multimeter: you won't be able to notice drop in resistance if only one turn of the winding (out of tens) is shorted. OTOH, inductance drops to almost zero and that leads to the sharp increase in STA driver current and its failure with smoke and all. The only thing you can reliably check is that none of the windings lost contact with connector but I don't recall anyone reporting IACV failure for this reason.

 

Calm down, plug ECU back, try to connect scan tool and start the car and come back with results. 2 things pointed to ECU from the start- inability to communicate with scan tool and SES light not coming up for check, otherwise there are few other reasons why the car wouldn't start. Are you sure your scan tool is OK? Are other dashboard lights off as well?

Just yesterday someone came here with similar issue (sudden no start; engine just died while driving) just to find out his 'old lady' drove over something and cut off wires from crankshaft position sensor under the car. The owner was very logical and quickly traced it down himself even though he had 0 previous experience. It's not the rocket science, really: car still needs gas and spark, that's all he was checking. 'Old lady' simply didn't notice that just before engine died she ran over something big .

 

Max_5gen, first off- thanks for the insight. That all makes sense, and sorry for "freaking out"- just feel I'm in a little over my head, dealing w/ ECU's, my boss's money and a car/make I'm un-familiar with, etc. etc. But I'm learning, thanks to y'all.

Anyway. I have no reason to believe the scan tool isn't alright; it's always pointed me in the right direction with this (and other) cars. And yes, all the other dash lights seem to work as they should, most even with the ECM disconnected.

Tomorrow I guess I'll get over there and put it back together, plug in the ECM and try my luck w/ the IACV un-plugged. Based on your post, though, it sounds like you're saying there's ultimately no way to "test" the IACV accurately, short of disassembling and inspecting the inner workings of it?

 

Even disassembling might not help, unless it is really in bad shape.
If I were you I would:
- check scan tool on some other car with the same protocol ISO 9141. Any Japanese car should do.
- put ECU and the rest together except IACV connector
- check battery voltage
- turn key to ON and try to communicate with ECU using scan tool
- if this fails I'd check +12V presence on all ECU pins it is supposed to be present. If it is present I'd talk to re- builder and bring this to his attention. There's very short path between ECU and scan tool and I never heard ECU being so 'confused' that it fails communication. It might not always give meaningful response but you have to get something back if it's alive.

You still can try to start the engine if the above fails 'just for laughs'. If you spray QuickStart into intake and then turn to START engine would 'try' to start if ECU gives at least spark. I don't have much faith in this though if ECU doesn't respond to scan tool.

 

Interesting. Alright, I'll keep you posted.

 

Alright. Well. A few successes tonight, but I'm not outta the woods just yet.

Put everything back together (including coolant bypass mod), left the IACV disco'd, and plugged in the computer. Turned the ignition on, and still no SES check light. Plugged in my scan tool and still no communication with the computer. Turned it over, for laughs, and no fire. Walked to the engine bay and noticed the (brand new) motor mount was buzzing again so I unplugged it and proceeded to check the engine control fuses. Aha! Engine Control 2 fuse was blown. I'm 100% positive I'd checked and re-checked every ECM fuse on the car when she very first had the no-start problem, but anyway. Decided to err on the side of safety and put a 10A fuse instead of a 15A.

Climbed back in, checked the ECM fuses inside-all good-and decided to turn the IGN back on, and wallah! SES light was on. Re-connected the scan tool and it was able to communicate. No codes were stored and it went straight to the data monitoring screen. So, decided I'd turn it over again. Turned over but wouldn't fire, and then the SES light went out again.

Hopped out and walked back around front to discover it'd blown the 10A ECM fuse again.

Not sure where to go from here.....why would the damned engine mount be buzzing when I JUST replaced it?? Could it possibly be due to the IACV not being connected? I'm really stumped.

 

very intersting issue i would lik eto see the outcome of this

 

Now you're talking . No, disconnected IACV can't blow the fuse, it's something else. IACV is not relevant to the mounts. This 'something else' is probably your primary problem. Let me look at FSM diagram what that fuse protects. I'd advise to put stock one (15A) there but let me check diagram first. Do you happen to notice fuse # by any chance?

 

If I'm not mistaken Engine Control 2 corresponds to fuse #59 which is located on the driver side of engine compartment in so called 'Fusible link and fuse box'.

Unfortunately, it powers many things besides ECU. One (actually 2) of those things are motor mounts. Since you recently worked on them - can you unplug both of them for now?

Another reason to blow that fuse and get 'dead ECU' condition is to pinch starter control wire while replacing the starter. I doubt it's your case as it would blow fuse right away while you were able to communicate with ECU for a short time but I mention it here as it's common mistake.

So, unplug both mounts, put 15A fuse back and try to start the car. Please do it slowly and pay attention- turn the key to ON, listen for fuel pump to build pressure, turn to ACC - look at the dashboard lights turning on and only then turn to START. You might want to slightly depress gas pedal to give it some air as your IACV is currently unplugged.

 

In the interest of full disclosure, I suppose I should mention that I did rebuild the starter sometime last year, but it's worked flawlessly ever since, but just since you mentioned that...

And yes, just last week I installed a brand new factory front motor mount (the one which was buzzing previously), although it is now disco'd. due to it buzzing again last night.

So anyway, I'll proceed to unplug the rear one, replace the fuse, and just pray that the fuse protected the ECM and it's not also fried. I threw in the towel last night after seeing that 10A fuse go haha

Will post results.

 

Would also like to say (again-full disclosure) that I'd read somewhere that a 4th gen'r had experienced a similar problem w/ blowing the ECM fuse, and finally tracked it down to a bum coil. I did replace one of the coils maybe less than a week before the no-start condition happened, and I have to say I was somewhat suspect of the quality of the replacement part. In the past, I'd replaced one and received what appeared to be a remanufactured OEM coil. This one was new and didn't seem to be as high of quality. Just mentioning.

 

It would help if you could identify blowing fuse for me from diagram below. Ignition coils are powered through #58 while mounts/starter - through #59. You should also check just in case if starter control wire is not pinched between starter and engine block.

 

You're giving up too easy - you finally got some results (ECU connected to scan tool) and verified that main problem you're having is ECU without power and still threw in the towel? Looking for short/failed electrical part blowing fuse is not fun but at least the problem is localized. BTW, the new mount is most likely OK - if I read you correctly it wasn't connected when the fuse blew the second time. This means it wasn't your primary problem. Leave it disconnected for now anyway.

 

haha I just meant I threw in the towel for the night; 9:30, pitch black out, about 200% humidity and probably 85* temp. = beer thirty.

IIRC, it's #58. Will also verify in a few hours. Will also double check starter control wire.

 

Please make sure which fuse is blowing before doing anything else. I was under impression it's #59 but if this is not the case it will be completely different story and I'll have to look at FSM again before I can say anything meaningful.

You're welcome to trace it yourself as well. If it's #58 disconnecting that coil of yours would be sensible step.

 

Alright, actually sitting beside the car as we speak.

The fuse in question was #59. Starter wire looks fine as far as I can see.

Gonna disco. the rear motor mount.

 

FINALLY! The car is running. Once again, a tremendous thank you, especially to Max_5gen.

I unplugged the rear mount, installed the correct fuse and it fired right up, no codes (initially). I let it get up to almost normal temperature and scanned it again and now it's throwing the IACV code, which is to be expected. Turns out the local stealership has one in stock, and our order online hadn't even processed yet so picking up the local one in the interest of finishing the project.

I'm presuming, due to all of this, that the rear motor mount was to blame all along. Sad that we replaced the front and not the rear, but for now anyway, I think we'll just leave them both disconnected and maybe cross that bridge another day.

 

Congrats, I told you it's not the rocket science .

I doubt IACV is faulty unless of course it didn't survive whatever you put it through: it is very unlikely 2 parts failed at the same time.

Disconnecting mounts never hurt anyone and nobody managed to notice any difference. Just put electrical tape on both parts of connectors. I also forgot that they were blamed for 'fried' ECUs in the past. Hard to confirm but they are certainly capable of blowing that fuse and creating such impression. That's how legends are born .

 

In hindsight, I'm kinda wondering about 2 things; 1, was the rebuilder honest in telling me there was failed circuitry in the ECM, and 2, was the IACV faulty in the end.

Had it been my personal vehicle, I may have probed a little further before concluding new parts needed to be purchased. As it stood, though, we were just at a point where something needed to be done to get the car running again.

 

1. I doubt but I'm suspicious type. As I said probability of 2 independent parts going bad at the same time is extremely low so is his chance to be honest.
2. No.
Looking back it was rather 'simple' fix - all you had to do was to disconnect rear mount and replace the fuse . Don't worry, I changed my share of parts on my own and it always surprised me why I didn't pick the most 'obvious' way from the beginning. Besides as my old friend who worked in service used to say: "Winners are not to be judged"- if you solved the customer's problem it's already a great success, even if you didn't take the shortest path. I'm pretty sure many stealerships would change ECU, IACV, mount and the fuse, most likely in this sequence and you would never learn the truth. Just read this board for a while and note how often people are paying for replacement of multiple parts while coming in with single problem. Either probability theory is utterly wrong or they are taken for a ride- your pick.

 

Yeah; in the blur (as it seems) of everything I ended up checking/thinking, it's difficult to say with absolute certainty, but I know I checked all the fuses and I also checked for voltage at the ECM connector and it had power in all the right places. Now, perhaps the end of the pliers were obstructing my view of the blown portion of the fuse, I don't know. But whatever. As you said- what's most important is that it's fixed now.

 

It also depends how you check the fuses. It sounds you do it by appearance. In 99% of the cases it works but I always check them with multimeter (for 0 resistance) to cover the last 1% . I came across few which looked perfectly fine but were blown anyway.

 

Good advice, and I think I did that myself, but again- after all the nights looking, thinking, tinkering, posting, etc. etc., it's all just a blur.

Now, it'll be a real win if I can sell the new motor mount to recuperate some money, since we're leaving them both unplugged anyway!