PDA

View Full Version : No CEL? And other o2 sensor questions...

98XJSport
September 4th, 2006, 08:12
I was just tinkering with my 98 XJ 4.0, and removed the rear o2 sensor to try in the front. I couldn't get the front sensor out, so I tried starting it to see if the heat would help. Long story short, no. But while running it without the rear sensor I didn't get a CEL at all, even after warmed up. Am I correct in thinking I should have?

Also, Ive heard that theres a fuse for the o2 sensor heater circuit. Any ideas where or what size fuse?

Thanks for any and all help.
98XJSport
September 5th, 2006, 04:16
No suggestions? It seems to me that it should have set the light...
goodburbon
September 5th, 2006, 04:31
The sensors are different, and cannot take the place of one-another. Other than that, put a scanner on it and see if it's throwing a code and the bulb is just burnt out.
98XJSport
September 5th, 2006, 08:56
I pulled the MAP sensor and it threw a code. So it's not the bulb.

I thought they were the same? I asked on here, seemed to be the general consensus...
98XJSport
September 7th, 2006, 06:27
Nobody? Seems as though a missing sensor should cause a cel, if not what could be wrong?
langer1
September 7th, 2006, 06:42
I think the back one don't but it still sets a code, not all codes turn the CEL on. The rear sensor is not part of the engine control system and so don't turn the CEL on.
98XJSport
September 11th, 2006, 09:49
Hm that could be, and it does make sense.

Are the upstream O2 sensors interchangeable from all 4.0 XJs?
mikejwil
September 11th, 2006, 10:00
Hm that could be, and it does make sense.

Are the upstream O2 sensors interchangeable from all 4.0 XJs?

From my own experience, 93 and 99 are different...so no. Hit napaonline.com and lookup various years. I suspect that 97-01 would be the same.
Smith2000
September 12th, 2006, 15:58
Nobody? Seems as though a missing sensor should cause a cel, if not what could be wrong?


I think an O2 sensor circuit failure takes a certain number of trip cycles to turn on the MIL. I'm almost certain it's more than 1, but it may be more like 10. I don't recall. I suspect the computer has a DTC in memory, it just hasn't detected the fault in enough trips to light the MIL.