My 98 trooper (3.5L 78K )has been having pretty bad gas mileage for quite a while (approx 13mpg city.
The other day it was about 100 degrees outside when my CEL light came on. I pulled off the highway, checked oil, radiator and a general check of the engine. No gross problems noted engine still running fine.
I pulled the codes that evening and the only code that showed was,
PO157 O2 sensor circuit low voltage (bank 2 sensor 2).
The printout suggested that this code can be caused by many different things including air, fuel, bad sensor etc.
When I checked the air filter (K&N)I saw that there was excess oil on the filter and some slight pooling in the bottom of the air box (half a thimble full). The air filter had been cleaned lubed and dried 5 months ago. My thought is that the excessive heat may have made the oil more fluid and caused the drippage. I haven't had a chance to check the MAF sensor yet. Edit..I just pulled off the MAF sensor and while its not sparkly I wouldn't consider it dirty (no fluid, no build up no gunk)
My thoughts are Check the fuel filter (read somewhere that a clogged or sluggish filter may cause a decrease in gas mileage and may lead to O2 sensor fault and finally search for the post detailing how to check the o2 sensor (IIRC I read a post about a year ago here detailing the procedure (any help with this would be appreciated).
If the CEL is still on does this indicate that the problem is ongoing? I know the code won't clear the memory for about 40 warm up cycles after the problem is fixed.
Am I on the right track? Any suggestions?
Thanks