All you ever wanted to know about your Check Engine Light but were afraid to ask - Nissan Forum
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post #1 of 169 Old Oct 19th, 2002, 12:24 PM
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All you ever wanted to know about your Check Engine Light but were afraid to ask

Hi folks,

I would've posted this on Altimas.net, but I figured it'd get lost in the static so I never bothered. You folks may appreciate it.

Recently, my 3.5's Check Engine Light (the FSM/ESM term is Malfunction Indicator Light, or MIL) illuminated in all its amber glory. The light presented with it no other symptoms, so I finished what I was doing that day, came home and threw myself into the ESM, which is rather less interesting than reading the dictionary, only more prone to put you to sleep.

The local network of wiring, sensors, controllers, chips and other various bits of silicon in the Altima is apparently vastly complicated, so I won't bore you (or me) by addressing it in detail here. However, one thing I found interesting is that the MIL shines only under two conditions:

1) If the ECM detects what Nissan considers a "serious" fault (such as a misfire), the MIL illuminates immediately and the ECM stores a trouble code.
2) If, however, the ECM senses a less serious problem, such as a vacuum leak, the MIL does not illuminate immediately. Instead, the ECM stores an identifying trouble code and waits to see if the same fault arises during the next trip cycle, which roughly corresponds to the next time you hop in the car and drive it around after turning it off. If the ECM senses the same fault, it trips the MIL light and you get to wade into the ECM or make the always-entertaining trip to your local dealer.

Your dealer uses a scan tool called a Consult to interface with the ECM directly. However, shadetree mechanics can manually pull the trouble code(s) from the ECM and, if desired, clear the code from memory, thus putting out the Check Engine Light, which incidentally shines like the fires of Hades at night against the dimmed gauge cluster.

To check the fault code yourself from the comfort of your own garage, put the ECM in "Diagnostic Test Mode II" by doing the following:

1) Sit your butt in the driver's seat.
2) Turn the ignition key to the ON position and wait three seconds. (Do not start the car.)
3) Fully depress and release the accelerator pedal five times in less than five seconds. (If you've got bad ankles, give up now and drive the car to the dealer.)
4) Wait exactly seven seconds. Fully depress the accelerator pedal and hold it down for about ten seconds until the MIL light begins flashing.
5) Release the accelerator pedal and start counting flashes to obtain the four-digit trouble code. Long flashes (0.6 seconds) indicate the first digit of the code; count the blinks one through nine and write down the first digit. (Ten blinks indicates a zero.) The next three digits follow in turn in the same fashion except with faster blinks (0.3 second) and a 1.0-second pause between digits.

The ECM code repeats intself until you turn the ignition key to the OFF position, at which point the ECM resets itself to standard get-in-and-drive-the-car mode. You can look up the trouble codes in the ESM/FSM; there's a bunch of them. In the ESM, refer to page EC-639. Additionally, if you get four blinks of ten (0000), the ECM is indicating no malfunction.

You can clear the code (and the annoying MIL) by holding down the accelerator pedal for more than 10 seconds while in Diagnostic Test Mode II. When you release the pedal, the ECM erases the trouble code(s).

In my case, my trouble code was 0442 - "Evaporative System Small Leak" - discussed on page EC-973. This could indicate anything from a poorly sealed gas gap to a leak in the evaporative recovery system underneath the car. I checked everything I could and decided to clear the code, thinking that maybe a slightly loose gas cap might've been the culprit. It apparently was, as the MIL hasn't shined since.

This is exactly the kind of problem that I hate -- hate -- having dealer monkeys diagnose, as it takes hours and hours for them to dirty up the inside of my car, change all my radio presets, go through my trunk and glovebox and grease up the doorhandles and hood before they wander over and say, "Well, it's fine now." Noooo thank you.

One other interesting bit (well, I thought it was mildly entertaining at least) I ran across while poring through the OBD section was that the ECM often changes engine behavior when it senses a fault. We've all seen the posts from folks whose engines wouldn't rev past 2400 rpm, for example, and seen them report the bad news their dealers had provided: The MAF gave up the ghost.

Well, that may well be the case, but the fact that the engine wouldn't rev past 2400 rpm is not because the MAF died. It's instead because the ECM sensed a two-trip MAF failure, illuminating the MIL and storing an MAF trouble code. When this fault is detected, the ECM limits engine rpm to 2400 as a "limp home" or self-preservation tool. This is all well and good, but it doesn't necessarily mean the MAF is dead; it simply means that the ECM thinks the MAF is bad. Bringing the car home, yanking the trouble code and clearing it will restore full engine operation until the ECM senses MAF failure again twice. And as anyone who works with computers or other electronic gadges knows, the more complicated the machine the more prone it often is to freak out occasionally with neither rhyme nor reason. Clearing out the code once before taking the car to the dealer and having him take the ECM's word as God's own before presenting you with an $800 bill for a new MAF in this case may well protect your checkbook and your sanity.

For those of you who've made it through my typical lengthy post, I salute you. The knuckleheads over at Altimas.net wouldn't have read past the third word, methinks.

Regards,

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post #2 of 169 Old Oct 19th, 2002, 12:29 PM
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Awsome info! Looks like we need to start ourselves a FAQ.


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post #3 of 169 Old Oct 19th, 2002, 12:31 PM
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fantastic! How long will it take before a lurker steals it?
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post #4 of 169 Old Oct 19th, 2002, 04:04 PM
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I told you guys I would find our very humerous and informative friend.....Welcome JK I missed you glad you joined us!
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post #5 of 169 Old Oct 19th, 2002, 04:22 PM
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That was great info. Glad you posted it, but be careful some of those monkeys that work at dealerships post here often and may even be Super Moderators, the iron fisted type. Hint, hint

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post #6 of 169 Old Oct 19th, 2002, 04:33 PM
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I didn't read the whole post but damn that's interesting.
post #7 of 169 Old Oct 19th, 2002, 04:40 PM
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Quote:
Originally posted by PatScottAKA99XE
That was great info. Glad you posted it, but be careful some of those monkeys that work at dealerships post here often and may even be Super Moderators, the iron fisted type. Hint, hint
Well if they are, we can only hope they can read, and that JK taught them something today
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post #8 of 169 Old Oct 19th, 2002, 04:53 PM
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Im gonna go a lil off topic for a moment since I am one of those "Monkeys"
Yep ill agree that many times the light is on cause the ECU had a brain fart and that there is no problem there. My dealership will, at the customers request just clear the code for free and send them on their way. If the like doesnt come back on thats cool, if it does and for the same code we will diagnose it. What we dont do however is just clear the code and send the customer off to see if it comes back with out the customers premmsion. You see we would get bitched at more for shipping it after clearing a code and it reappears, then we would if we spend 3 hours trying to diag a problem that is not there. Here is the major difference though.. If we spend 3 hours trying to diag a problem that is not there, we do not charge the customer one cent, and we give them a free wash and vac for wasting there time.
I guess the dealers that you guys go to are dicks IMO. If I were you I wouldnt pay a cent if they dont find a problem and make them wash and vac my car.

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post #9 of 169 Old Oct 19th, 2002, 06:03 PM
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Quote:
Originally posted by PatScottAKA99XE
... but be careful some of those monkeys that work at dealerships post here often and may even be Super Moderators, the iron fisted type.
No offense meant, PatScott. I don't believe that all Nissan technicians are monkeys. Since you take the time to post on a Nissan enthusiast forum, you probably take your job and your craft very seriously. That being said, I'm sure you'll agree if you've worked as a dealer technician for any length of time that the ratio of dain-bramaged dunderheads to meticulous, qualified master craftsmen is skewed just slightly toward the former at most Nissan dealers.
Quote:
If we spend 3 hours trying to diag a problem that is not there, we do not charge the customer one cent, and we give them a free wash and vac for wasting there time.
Wash and vacuum? Free? What the heck is that? My wife's Infiniti dealer does that sort of thing while providing croissants on a white linen napkin, but sadly her car has been so rock-solid reliable that she's only seen the inside of her dealership once. I, on the other hand, have become practically intimate with my Nissan dealer, and while I've been fortunate in that each time I've taken the care in for repairs the work has been done well and generally on time, each time I've gotten the car back I did a double-take to make sure the pewter Altima they gave me was in fact my car. Just about everything that could move, be adjusted, changed or modified was moved, adjusted, changed or modified. And the car was invariably dirtier and greasier than when I brought it in.

Nonetheless, I'll say this: If I've got the choice of getting my car monkeyed and returned waxed and vacuumed or repaired well and handed back to me grungy and with all the station presets changed to rap music, well, sign me up for the second one. Maybe I should just bring the car to you, PatScott. You sound like a good guy.

Thanks for the kind words, everyone.
post #10 of 169 Old Oct 19th, 2002, 06:15 PM
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No offence taken. Sorry if it sounded like I was. Unfortunatly I dont work at a Nissan shop. GMC dealership for me(I, know).

Maybe where I am us techs are different. None of the guys at my shop would move your seats, mirrors, ect. The only thing we may do is turn the radio off, not change the station. If we get any grease/dirt on/in the car.. it goes over to to cleaned before the customer gets it.

We are a small shop, we only have 5 technicians. The reason we dont clean a car after *every* job is that we only have one wash guy, it would be impossible. We are VERY small in other words.

I dont think you would want to drive to NH to get your car serviced by me even though it would be a welcome break from the GM stuff, and from the sounds of things you wont catch me working in that shop you go to.

Good info, and keep up the good posting.

Pat
*edit*
That comment about the tech ratio.. Its not just Nissan shops. Trust me

Patrick Scott
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post #11 of 169 Old Oct 19th, 2002, 06:55 PM
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Real Good Info!

Excellent as always JK, I read it all and then my computer froze.

Willy said he tracked you down and I say sincerely, Welcome.

btw, my computer has been freezing a lot lately so don`t take it to heart.


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post #12 of 169 Old Oct 19th, 2002, 07:18 PM
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Make it stop! Intellectual posts! ARGH! Headache!

Quit it, immediately!
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post #13 of 169 Old Oct 19th, 2002, 11:33 PM
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Jarrod.. all I can say is wow... awesome post.. That will be a life saver for many.. Also.. welcome aboard..

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post #14 of 169 Old Oct 20th, 2002, 07:30 AM
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Originally posted by scottlny
Jarrod.. all I can say is wow... awesome post.. That will be a life saver for many.. Also.. welcome aboard..
Ya... What he said.

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post #15 of 169 Old Oct 20th, 2002, 09:57 AM
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Thanks again, guys. Now if I can get you people whom I know to stop changing your handles from forum to forum, all will be right in my world again.
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