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Unread 09-07-2011, 01:37 PM   #1
ecpage
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2000 Cherokee Oxygen Sensor Dilemma

Hey guys. I have a 2000 Cherokee and I recently had the check engine light come on. Long story short, it appears that both O2 sensors are shot (P0132, P0135, P0138, P0141).

Here's the kicker...my Jeep runs fine and my fuel economy has actually gotten BETTER since the light came on. If I have to do something that requires disconnecting the battery it runs rough for a few days but then smooths out. I guess my question is this...since I'm getting increased fuel mileage and everything seems to be running fine, if there any real reason to replace the sensors?

Thanks to anyone that reads or responds to this post.

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Unread 09-07-2011, 01:45 PM   #2
XJH-007
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Check engine light still on? If so.....passing emissions will be hard (if you have them)

Clear the codes and drive it....it could have been a glitch in the matrix that has passed.

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Unread 09-07-2011, 03:03 PM   #3
AmbuGrl
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Bad O2 sensors cause your mileage to worsen not get better.
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WTF is Clockspring??? my Jeep has digital clock
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Unread 09-08-2011, 02:22 AM   #4
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Quote:
Originally Posted by XJH-007 View Post
Check engine light still on? If so.....passing emissions will be hard (if you have them)

Clear the codes and drive it....it could have been a glitch in the matrix that has passed.

Well, yeah...the light is still on. I wouldn't be posting if it wasn't.


Quote:
Originally Posted by AmbuGrl View Post
Bad O2 sensors cause your mileage to worsen not get better.
No kidding...that's my point. And yet here I am with two bad O2 sensors and about a 15% increase in fuel economy.
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Unread 09-08-2011, 03:52 AM   #5
tjwalker
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You have two codes that are related to the HEATER circuit of both your upstream and downstream oxygen sensors.

It is possible, but it is highly unlikely that both sensors went bad at the exact same time.

What is more likely is that you blew the fuse to the heater circuit. The fuse for this is located inside of the power distribution center (the black box under the hood on the passenger side). I'm not sure of the exact location, but somewhere in the 10-17 slot range. It definitely is a 15 amp mini fuse though. Jeep did a disservice by not labeling the PDC cover with all of the pertinent information. So inspect or better yet, put a meter on all of those mini-fuses to verify their condition.

You MUST verify this fuse before condemning your oxygen sensors. It very well could be the root cause, and is not that uncommon on the 97-01 4.0 engine; I answer threads about this every month or so, and just helped a guy with this exact same problem on another XJ forum. I hope this is your problem.
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Unread 09-08-2011, 07:46 AM   #6
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Quote:
Originally Posted by ecpage View Post
Well, yeah...the light is still on. I wouldn't be posting if it wasn't.

No kidding...that's my point. And yet here I am with two bad O2 sensors and about a 15% increase in fuel economy.
Kinda sarcastic replies for needing our help little buddy.


If your motor is running too lean it can get too hot, and also burn holes in your pistons....but I bet you already knew that too.....

Do as TJwalker said, clear the codes...and see what happens.
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Unread 09-08-2011, 08:05 AM   #7
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Quote:
Originally Posted by AmbuGrl View Post
Bad O2 sensors cause your mileage to worsen not get better.
That depends on the nature of "bad."

If your watch is "bad," are you going to be early or late?
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Unread 09-08-2011, 09:15 AM   #8
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Quote:
Originally Posted by tangofox007 View Post
That depends on the nature of "bad."

If your watch is "bad," are you going to be early or late?
depends

is it running fast or slow
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Quote:
Originally Posted by RacerX View Post
WTF is Clockspring??? my Jeep has digital clock
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Unread 09-08-2011, 09:22 AM   #9
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I've always been a "the Glass is twice as big as it needs to be" person myself.....

Since time is really just a measurement from one event to another, it's individualistically relative (we all view and experience time differently). So if there's no "good" or "bad" events to focus on time seems to stand still.

I've been watching too much Into the Wormhole....
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Unread 09-08-2011, 09:26 AM   #10
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Quote:
Originally Posted by AmbuGrl View Post
depends

is it running fast or slow
Same applies to "bad" oxygen sensors. "Bad" can result in mixtures too rich or too lean.
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Unread 09-08-2011, 09:31 AM   #11
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Quote:
Originally Posted by XJH-007 View Post
Do as TJwalker said, clear the codes...and see what happens.
How does one go about clearing the codes?

Lately, I've been getting an intermittent Check Engine light. Comes on for while, then goes away. I too was thinking one of my sensors is going out. But I thought that once the light comes on, it basically stays on for x number of starter cycles.
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Unread 09-08-2011, 02:28 PM   #12
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Unhook the battery to clear codes. Put a OBDII-compatible tester on it.

I'll skip mentioning time unless the warp won't let me not notice.
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Unread 09-08-2011, 02:59 PM   #13
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Quote:
Originally Posted by lucky9 View Post
Unhook the battery to clear codes.
Well, that makes sense. Thanks!

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I'll skip mentioning time unless the warp won't let me not notice.
Huh???
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Unread 09-08-2011, 07:09 PM   #14
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Fyi

Just puttin this out there... my 2000 sport had pinched wires in the o2 sensor harness that runs over the top of the tranny. The guy that changed out my engine found them and also found wires with bad insulation running along the the firewall. Some techs have figured out how to cheat the computer connections so they read good sensors... it's easier than chasing down bad wires. Best of luck to you!
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Unread 09-20-2011, 11:53 AM   #15
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Quote:
Originally Posted by XJH-007 View Post
Kinda sarcastic replies for needing our help little buddy.
The answers I was replying to weren't thought out very well. Asking if the check engine light is still on is silly considering there are people advising me to clear the code and "see what happens"...the logic being that if the check engine light is off, things are OK. So if the check engine light was off I wouldn't be asking about it, right?

Same for the reply about O2 sensors ruining your gas mileage. I mentioned in my post that my fuel economy had actually gotten BETTER...so what do I say to someone who declares something to be the exact opposite of what I have said (and can prove) to be the case?
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