rbuswell

OK so I checked the CEL sticky thread and didn't see anything about this problem. My 1998 GXE automatic will illuminate the CEL for no apparent reason but when I check it with a reader there isn't any DTC code at all. There was one instance where the CEL came on and went off after about four days then came on again.

The car runs really well with the mods I've done. One mod I did, that I don't think is the issue, was from VQpower.com that defeats the speed limiter. I installed a switch on the wire I snipped for this mod and it appears to work correctly. When I turn off the switch (breaking the circuit on the wire) the proper code shows up for a speed limiter malfunction when reviewing the DTC codes. When I turn it on (completing the circuit) the code doesn't show.

What this means is that 1) the DTC code that triggered the CEL is going away somehow, which I didn't think an OBDII ECM would do, 2) there is some sort of other malfunction like a clocking problem with the ECM or 3) the speed limiter mod does something to the ECM that shows up regardless whether the circuit is complete or not.

Any ideas, guys?

PH98I30

Sometimes the CEL light will glow when your alternator is starting to go out. It will not throw a code.

rbuswell

I'll check it out and keep an eye on it going forward. It has been going on for many weeks and there's been no indication of the battery draining down. Thanks for the tip.

CS_AR

This and I've seen a battery that is starting to short wreak all kinds of strange ECU behavior.

rbuswell

The battery sat on a trickle charger for a long time while I was doing the mods. It isn't that old but it could be going downhill because of that, too. Another good tip and I will check it out as well.



BTW, are you suggesting that the battery damaged the ECU or that it is just making the ECU act funny?

CS_AR

Just making it act funny.. Not long ago I got a real scare on my 2006 Honda from a battery that started to have a short problem. The 36-month battery was at 40 months. So the vehicle drove just fine to a car show that afternoon. When I got in it to leave the show, the VTM4 (AWD system) system lights started flashing along with a CEL. I thought the ECU or the VTM4 system controller was toast and I was in for a $1,400 repair bill. Then I remembered the battery was over 36 months old. So I drove straight to the part store and got a new one installed on the spot. That ended the crazy codes problem. That was last summer. No further issues. Earlier in the year, I had a shorted battery on the 99 I30 knock out an alternator. So I've learned, albeit the hard way, to just replace a 36-month battery soon after 36 months to keep the electrical system healthy and happy.

Turbobink

iTrader: (2)

Based on the explanation you provided in your initial post, I'm assuning you own a scan tool.

That being the case, I'd maintain the scan tool connected continuously while I'm running the car and see if the tool can catch the intermittent code.

rbuswell

You are correct. I have a tool, actually software called OBDCOM that runs on my laptop with a cable that plugs into a USB port and the car's OBDII port.

The CEL isn't really intermittent. After I reset it, the CEL stays off for a period of time, maybe twenty to thirty miles of driving, then it comes on again and stays on. I don't think it has come on after resetting while the car is at idle. It seems to only happen when the car is being driven. It doesn't seem to matter if the car has been run continuously or been turned off and on. It doesn't seem to matter how fast I'm driving or the ambient temperature.

I had never heard of a DTC being thrown and then the ECU corrects itself. I always thought that a code stays in memory until you clear it. That's why I'm thinking it is some other clocking issue or something like that.

I like the idea of plugging the reader/laptop in and just driving it until the CEL comes on to see if there is a code that somehow clears itself. Thanks again, guys, for all the input and ideas.

rbuswell

I would never guess that a battery could cause all that. Definitely food for thought.

Turbobink

iTrader: (2)

Your CEL symptom is typical of a clogged/restricted EGR guide tube.

IIRC the DTC is P0400.

rbuswell

That makes sense as to the symptoms that the ECU would pick up. No code however. I've also had that area of the engine apart very recently for some other problems and didn't see the same kind of caked-on build up that the various Maxima.org EGR guide tube threads illustrated. The other thing that makes me wonder if that's it is how well the engine runs. I've had EGR issues on other cars (not the Maxima) and the engine ran like crap.