OK.... I had a CEL which indicated I had an O2 sensor issue.  I had already replaced my down stream O2 sensor so I installed a new upstream O2 sensor, then drove Buster for about a week.  Then one day my CEL came back on.  I took it down to Day's for Don to read the problem... but the computer wouldn't let the analyzer read the data.  So I figure I have a fuze or a ground issue.  

I checked my fuzes under the driver side dash, checked my fuzes under the hood.  All appeared to be good, as in they were not burnt.  I reseated (pushed) on all the fuzes and relays.  I got in Buster and headed down to Day's again and noticed my CEL was off!  Hmmm?  So I decided to run him down the road and went to visit a friend.  All is good.  Jump forward about four or five days and suddenly the CEL comes back on.  I'm going to stop by Day's again to see if the error codes can be read this time.

Anyone have any ideas on this gremlin?  I'm of the mind it has to do with a ground someplace.  Somewhere around one of the fuze boxes...?

First item is to stop and get a OBDII code reader, around 25$ for a basic OBDII reader.

Seldom does the secondary o2 sensor(downstream) fail, it's only function is to read the post cat o2 levels to verify the cat is functional, more apt to be a whanky cat.

Also, pull ECU power for 60 seconds and allow the ECU to reset for winterblend fuel.


ps: it is fuse, not fuze.

I have the same issue with mine.  Apparently the computer needs to read the fault 2 consecutive times before it triggers the CEL.  Mine seems to turn on every few days and then go back off.  I am suspecting a faulty wire or connection somewhere. Hence the intermittent fault.

Well, I got a P0131 reading today, which indicates a low voltage reading in the O2 sensor.  The hi to lo voltage spread for the sensor is around 100-900mv.  So I guess I will check the O2 connectors (again), clean a few sensors upstream like at the intake and clean the PVC  again and check some vacuum lines for leakage.  I think I'll just pull the air filter and spray some carb cleaner up into the intake at high idle.  The computer is only supposed to trip the CEL when it reads a low reading for 'more than 2 minutes'.  My MPG is way down so I am thinking the computer is reading the exhaust as 'lean', that it figures the engine is being starved for fuel and is increasing the fuel mixture = worse fuel economy.  Hmmm.

Buster still runs like a top, though.  Just not as economical as he was.  I just topped off the fuel tank and figured my MPG and it reflects 20-21 MPG which is way down from where he should be.  Honestly, when I first made the tire and gear changes, I clocked a freakish 29MPG average going to Nashville, TN (340 miles).  Even IF I were off by a half gallon on the refuel calculation (different pumps, etc) I should be pulling an honest 25-26 MPG easily.  On the return from Nashville that trip, I had to go cross-country to pick up some bee supplies (I'm talking the hills of Kentucky, here) and even then when I arrived home I averaged 25MPG.   I'd be happy to get back to 24MPG if the local gas stations are now pumping their winter blend.  3-4MPG is a significant difference... about 50-70 miles less per fuel load.

I disconnected my neg battery cable last week after the CEL went off after screwing around with the fuses.  I thought I had waited for at least a minute, but that's easy to do and I'll "do it again.'  FuSe.  Got it.  I was typing fast and not looking hard.  Thanks.

Ok. Mine is different. I have the no readings fault.  I am planning on putting in a new sensor and driving forward from there.  Best mileage in the GV was 24mph with stock tires all highway.  More like 21mpg now with the larger all terrains.

LOL, I always figure it is that infernal autospell thing, LOL

also make sure there is no exhaust leaks prior to the primary o2 sensor.

WILCO.  Thanks, T.

OK, performed all of the above, reset the computer... no light.  Now to driver Buster a few miles/days and cycle the computer a few times and wait to see what pops on.

A 30 minute ride with at least 10 engine starts and stops, both city and highway driving, should enable the readiness condition and do full OBDII checks.

First item is to stop and get a OBDII code reader, around 25$ for a basic OBDII reader.

Seldom does the secondary o2 sensor(downstream) fail, it's only function is to read the post cat o2 levels to verify the cat is functional, more apt to be a whanky cat.

Also, pull ECU power for 60 seconds and allow the ECU to reset for winterblend fuel.


ps: it is fuse, not fuze.

Drone637 just got me a Bluetooth OBD 2 reader that I use my phone to scan.  I leave it hooked up all the time and check it whenever a code comes in.  They are about your $25 at Amazon.

My computer tells me which 02 analyzer has no voltage, and if the #1 sensor on either Bank 1 or 2 has no voltage, the motor will run very lean, with poor mileage and low power (constant downshifts).

That's interesting, Board Hunter.  Real time system checks and monitoring.  My CEL was off for a couple of days... then came back on while I was traveling north to hit some trails (about 70 miles away).  I came home from the trail ride, stopped enroute at a car wash to blast the excessive mud off of Buster (it started raining on the way up and rained the entire time I was driving trails).  I hopped back in the truck, fired him up and... and the CEL was off.  It came back on again this afternoon (two days later).  I ordered an O2 extension from Summit Racing (a Vibrant Performance product - thanks for the part number talonxracer)) a couple days ago.  I will install it on the downstream sensor and see what happens.

Oh yeah, the Mastercraft C/T tires did well in the mud.  Much better than the BFG A/Ts.   As well as I had hoped for and as well as the Wranglers and Rubicons there running M/Ts did.  There are different kinds of mud.  This mud wouldn't clear out of the lugs even with wheel spin... for anyone.   Still, I went everywhere the Rubicons went EXCEPT through two tub size drop-offs with really steep exit shelfs.  I didn't have the front clearance and my brush guard plowed the terra firma pretty good trying in one case.  I totally packed the lower brush guard and the front air vents in the bottom of the plastic bumper cover solid.  The brush guard took the brunt of it, and the bumper wrap remained in tact.  Yup, a Rubicon tugged me out of both of them.  Still, for running the shortest tires in the group (29") I'm good with it.   It is what it is.