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88JeepXJ
October 12th, 2006, 12:14
Just had my CEL scanned. Besides my known "large and small vac leak" I also got a code for the 2nd O2 sensor. Does this affect gas mileage? I remember it only telling you how the cat performance was doing. Obviously I hope it is just the second O2 sensor (~$60) and not the car ($200).

UNCC_99XJ
October 12th, 2006, 15:54
The 2nd o2 sensor does not affect milage....it is merely there to keep an eye on the cat. I'm fighting the same problem with mine...have been ever since March....just barely passed inspection this week (light came on while traveling home from the place i had it inspected at). Every time I check that stupid sensor there is nothing wrong with it. I've just learned to clear the code and go on about my business...hell, most of the time, the light will go back off on its own after a few restarts.

88JeepXJ
October 13th, 2006, 06:24
Damn OBDII...I never had to deal with this on my 88 or 91.

I still haven't looked into the vaccum leak other than replacing the fuel cap...not it.
Is there a ~1/2" vac hose that runs from under the gas tank all the way to the engine bay? If so does this fail often and cause a vac leak?

UNCC_99XJ
October 13th, 2006, 07:16
It would probably help if you posted the specs on the XJ we're talking about....i.e. year, milage, engine. etc...

langer1
October 13th, 2006, 08:17
I the "large and small vac leak" also a code?

88JeepXJ
October 13th, 2006, 09:09
It would probably help if you posted the specs on the XJ we're talking about....i.e. year, milage, engine. etc...

Yes it would :)

'99 Classic, 4.0, AW4, 96k miles