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Unread 03-22-2007, 09:26 AM   #1
Jonasty
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O2 Sensor Fuse/Relay

Well, of course, like everyone else, my jeep has not-so-great gas mileage. I realize that there really isn't much I can do to fix this; however I did have one questions about the oxygen sensor system.

In the fuse box under the hood (I think it's called the PDC?), there seems to be some fuses/relays (don't really know what they are) missing where the diagram says the O2 sensor fuses/relays should go. Does this mean that previous owner took these out or were they never there?

There are also ones missing under the ABS part of the diagram, but I don't think I have ABS.

Any help is appreciated.

EDIT: I don't have an owner's manual and I checked my Haynes and I can't find anything about it.

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Unread 03-22-2007, 02:46 PM   #2
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Unread 03-22-2007, 04:21 PM   #3
Stu Olson
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I believe the PDC in our TJs was also shared in some other models.

Your TJ does not have a relay that powers the O2 sensors. (per the FSM)
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Unread 03-22-2007, 06:26 PM   #4
Goose346
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Quote:
Originally Posted by Stu Olson
I believe the PDC in our TJs was also shared in some other models.

Your TJ does not have a relay that powers the O2 sensors. (per the FSM)

Per the 2000 Wrangler Service Manual, The Power Distribution Block uses cavities B11, B12, B13 and B15 for the downstream O2 sensor relay and B16, B17, B18 and B20 for the Upstream O2 sensor relays.

Fuse #17 (20A) provides power to these two relays. If you are having issues, you would be running real rich and passing black smoke!

You may want to check your upstream O2 sensor and or your MAP sensor. With 100K on my vehicle, I just replaced them and I am running real good now.
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Unread 03-22-2007, 08:11 PM   #5
tandbwms
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Seems like if your O2 sensors were not working because the fuse was pulled then your check-engine (MIL) would be on. Does the MIL still work? You are right that if the O2 sensors were disconnected you would get poor gas mileage. The PCM would make a best guess at fuel trim based upon the MAF, but it wouldn't be able to identify a rich or lean condition from combustion.
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Unread 03-22-2007, 09:25 PM   #6
Jonasty
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Well as far as I can tell, those relays are gone. I'll have to take another look again tomorrow just to be sure. The check engine light isn't on, but then again, I've had this TJ for about two months and the previous owner may very well have broken the bulb or something so it didn't work (had that happen in a car I used to own). I get about 15 mpg highway which isn't as bad as some on here, but I wouldn't mind better. The stealership quoted me $15 for the relay but I'm going to have to look around to possibly find a better price.
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Unread 03-22-2007, 10:48 PM   #7
Stu Olson
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Quote:
Originally Posted by RAG48
Per the 2000 Wrangler Service Manual, The Power Distribution Block uses cavities B11, B12, B13 and B15 for the downstream O2 sensor relay and B16, B17, B18 and B20 for the Upstream O2 sensor relays.

Fuse #17 (20A) provides power to these two relays. If you are having issues, you would be running real rich and passing black smoke!

You may want to check your upstream O2 sensor and or your MAP sensor. With 100K on my vehicle, I just replaced them and I am running real good now.
Could you look in the wiring section and tell me what these relays do in regards to the O2 sensors?

I stole my buddy's '04 FSM and looked it up. The O2 relays are only used on export/Japan low emission models.

Are you saying that in '00, they used them in the US models? I realize that things do change from year to year....but then again, it seems rather odd that DC went from no O2 relays to using them and then back to not using them again.
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Unread 03-23-2007, 01:38 AM   #8
Jeepguy1977
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I don't remember which fuse it is under the hood, but in my 98 Sport, the O2 sensors are on the same circuit as my fuel injectors.....don't ask how I found this out.......
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Unread 03-23-2007, 06:07 AM   #9
Goose346
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Quote:
Originally Posted by Stu Olson
Could you look in the wiring section and tell me what these relays do in regards to the O2 sensors?

I stole my buddy's '04 FSM and looked it up. The O2 relays are only used on export/Japan low emission models.

Are you saying that in '00, they used them in the US models? I realize that things do change from year to year....but then again, it seems rather odd that DC went from no O2 relays to using them and then back to not using them again.
Wrangler Service Manual Page 8W-10-14

Upon further review, these relays are only included on models equipped with CALIFORNIA emissions
Batt---20A (fuse) Power Dist Center - - - - line split to --- O2 Sensor Upstream Relay and O2 sensor Downstream relay

Upstream relay wires - A14, 18, DG to upstream sensors (2) in pipe
Downstream sensor A242, 18, VT/OR to downstream sensors (2) in pipe
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Unread 03-23-2007, 03:56 PM   #10
tandbwms
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Concerning the MIL being burned out - when you turn the key to the "key on/engine off" position the MIL should be on. It's like that so you can verify the light works. Give it a check, if it is off then no worries. Everything is working as designed. If the O2 was disconnected, the MIL would absolutely be on.
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