Topic: CEL from nowhere

[YJ KiD]

alright guys i have a odd CEL that comes on only after about 70 or so miles of continous driving (highway) and when i go to chck the code and get to the closest autozone or orielly to have the code read when i turn it off to get the code the light goes off and will not come on again for another 70 miles.  All the fluids are good and it runs great it has done this as long as i have owned it for the last 3 years and has never got hot or done anything odd except for this dang light coming on.  The only yhing that might help is that the higher i run it in the rpm band the less miles it takes it to come on. 

Any help would be much appreciated
Thanks in advance 

[Jeffy]

You don't need a reader to get a CEL code from a OBDI YJ, which is what I'm assuming you have.  Do the ignition trick and the code should be displayed.  I'm suspecting it's an O2 sensor though.

[sharpxmen]

I could be wrong but i thought the last code store is stored even if the light goes away.

[YJ KiD]

I assumed that when the light went away the code was gone i will go check and see if i can get it . . . . .anyone know where i can find the list of codes?

[YJ KiD]

the codes that popped up was an A/C relay which my jeep doesn't have A/C (not the original motor) and that the battery has been disconnected so no real issues but any ideas on how to bypass the A/C relay or where it is even located

[Jeffy]

So it's intermittent.  You're going to want to check for the code as soon as you stop someplace.  If it's intermittent then it might not get stored.  You might have to wait and see if it gets worse so it actually stores a code.  Could be a missfire or a O2.

[sharpxmen]

. . . . .anyone know where i can find the list of codes?

in the FAQ section on this site

[YJ KiD]

what do u mean by intermittent it happens every time i drive it as described and if it hasn't gotten any worse over the last 3 years so i dont know if it will if it was a misfire or an O2 wouldn't the code have popped up when i checked them this afternoon

[dwtaylorpdx]

I have a very similar problem, but only when the outside temp is over 82 degrees.

Acts like the fire goes out in the engine, takes 70 to 100 miles or a long pull up a steep grade to set it off.

Hmm.

Dave

[Bounty Hunter]

Mine used to do the same thing, hasn't done it since I replaced the o2 sensor.

Not every code is a hard code that sticks around and is readable once the jeep is turned off.

[YJ KiD]

sounds like i will change the o2 sensor and see if that does something maybe it will work and if it solved the problem for someone else hopefully it will do the same for me.  Still dont get what is the difference between an intermittent and constient CEL what is the difference, not trying to sound dumb so please explain the difference if is not to lenghthy if possible please as i have not worked to much with any kind of fuel injection,  mostly a carb guy not to sound dumb   

[dwtaylorpdx]

You can test the O2 with a needle style volt meter.  If its flicking back and forth between the appropriate voltage its fine.

I can't remember the exact voltage but its a quick easy test.

Dave

[sharpxmen]

You can test the O2 with a needle style volt meter.  If its flicking back and forth between the appropriate voltage its fine.

I can't remember the exact voltage but its a quick easy test.

Dave

it's 0 to 1 volt roughly (think it's actually 0.5 to 0.95) but it's quite fast for a needle voltmeter, should average at about 1/2 volt in closed loop - you can figure out if you have voltage though.

[dwtaylorpdx]

Sounds right, I find the needle voltmeter will quiver about 1/2 way between the points and bounce to them occasionally, where a LCD will just show peak, unless you have one that stores low and high number ! , or an oscilloscope will show if its function is good. Also if you take the O2 off I think Autozone can test it for base function.

Dave

[sharpxmen]

Sounds right, I find the needle voltmeter will quiver about 1/2 way between the points and bounce to them occasionally, where a LCD will just show peak, unless you have one that stores low and high number ! , or an oscilloscope will show if its function is good. Also if you take the O2 off I think Autozone can test it for base function.

Dave

my autometer led afr gauge will actually bounces really fast between lean and rich in closed loop and go towards rich once the pcm goes in open loop - it will flicker back and forth in both instances, a bit slower in closed loop and on a reduced range on the rich side in open loop, when my O2 died only the last led on the rich side was lit, so I could tell right away that was why the CEL came on. pretty informative especially if you want to get best mpg - trying to keep it in close loop save the most fuel.