O2 sensor questions
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Junior User
Joined: Jul 2003
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From: Shawnee KS
O2 sensor questions
Hey all. I have been having trouble with my '97 EB Expedition running very rough. I had it to a shop and we replaced all the spark plugs. At that time the mechanic said that the 'cat sensor' was the only error code he was getting. Well back on the street it was still running rough and the good ol check engine light was on. Took it to Advance Auto Parts today and the codes it read were 141 and 301. I guess 141 is O2 sensor #2? Is this the same as the cat sensor? Would just an O2 sensor cause the rough idle and misfires? Any help is appreciated. Thanks for the long read!
Postmaster
Joined: May 2002
Posts: 3,028
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From: Annapolis, Maryland
O2 sensor questions
The Expedition essentially has 3 02 sensors - one in each header, and one behind the cat. The 02 sensor behind the cat is really only used to be sure the cat is functioning properly.
The purpose of an 02 sensor is to analyze the exhaust gases and use the information to manipulate the air/fuel mixture. When it starts misreading (due to age, carbon buildup, etc.) it will cause gas mileage loss and general mixture problems.
The cat sensor is pretty easy to fix. The other two are a PITA. Let me know if you'd like precise directions.
XXL
The purpose of an 02 sensor is to analyze the exhaust gases and use the information to manipulate the air/fuel mixture. When it starts misreading (due to age, carbon buildup, etc.) it will cause gas mileage loss and general mixture problems.
The cat sensor is pretty easy to fix. The other two are a PITA. Let me know if you'd like precise directions.
XXL
Postmaster
Joined: May 2002
Posts: 3,028
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From: Annapolis, Maryland
O2 sensor questions
Not sure about the codes; somebody else on here should be able to tell you about them.
As far as the 02 sensor change goes, it's not for the faint-hearted. You have to work in a very cramped area, and it's very aggravating. At first it looks impossible, but it can be done. You have to jack up the front end, pull off the front wheels, undo the bolts that hold the wheel well plastic shroud thing in and pull it back. Then you'll have access. The driver side one is easier than the passenger - you need to use a small flathead screwdriver to detach the electrical connection (you just shove it up in the slot and the connection comes loose). The passenger side is a doozy - same process, but you also have to take out the tranny dipstick tube. The dipstick tube is held onto the block with 1 bolt/bracket, and it has a "pop" connection to the tranny - just pop it out/in. Believe me - this job is IMPOSSIBLE without removing the dipstick tube.
Let me know if you need more precise directions.
XXL
As far as the 02 sensor change goes, it's not for the faint-hearted. You have to work in a very cramped area, and it's very aggravating. At first it looks impossible, but it can be done. You have to jack up the front end, pull off the front wheels, undo the bolts that hold the wheel well plastic shroud thing in and pull it back. Then you'll have access. The driver side one is easier than the passenger - you need to use a small flathead screwdriver to detach the electrical connection (you just shove it up in the slot and the connection comes loose). The passenger side is a doozy - same process, but you also have to take out the tranny dipstick tube. The dipstick tube is held onto the block with 1 bolt/bracket, and it has a "pop" connection to the tranny - just pop it out/in. Believe me - this job is IMPOSSIBLE without removing the dipstick tube.
Let me know if you need more precise directions.
XXL
Senior User
Joined: Feb 2003
Posts: 369
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From: Bronx, New York
O2 sensor questions
Originally posted by BigMattXXL
Not sure about the codes; somebody else on here should be able to tell you about them.
As far as the 02 sensor change goes, it's not for the faint-hearted. You have to work in a very cramped area, and it's very aggravating. At first it looks impossible, but it can be done. You have to jack up the front end, pull off the front wheels, undo the bolts that hold the wheel well plastic shroud thing in and pull it back. Then you'll have access. The driver side one is easier than the passenger - you need to use a small flathead screwdriver to detach the electrical connection (you just shove it up in the slot and the connection comes loose). The passenger side is a doozy - same process, but you also have to take out the tranny dipstick tube. The dipstick tube is held onto the block with 1 bolt/bracket, and it has a "pop" connection to the tranny - just pop it out/in. Believe me - this job is IMPOSSIBLE without removing the dipstick tube.
Let me know if you need more precise directions.
XXL
Not sure about the codes; somebody else on here should be able to tell you about them.
As far as the 02 sensor change goes, it's not for the faint-hearted. You have to work in a very cramped area, and it's very aggravating. At first it looks impossible, but it can be done. You have to jack up the front end, pull off the front wheels, undo the bolts that hold the wheel well plastic shroud thing in and pull it back. Then you'll have access. The driver side one is easier than the passenger - you need to use a small flathead screwdriver to detach the electrical connection (you just shove it up in the slot and the connection comes loose). The passenger side is a doozy - same process, but you also have to take out the tranny dipstick tube. The dipstick tube is held onto the block with 1 bolt/bracket, and it has a "pop" connection to the tranny - just pop it out/in. Believe me - this job is IMPOSSIBLE without removing the dipstick tube.
Let me know if you need more precise directions.
XXL
Matt is 100% on the money, my bleeding knuckles will attest....I do believe there are 4 O2 sensors on the vehicle. 2 ox. sensors, and 2 "cat monitors" . They are all the same part #, and bank 1 is the pass. side, bank 2 is the drivers' side. The reason for 2 "cat monitors" is there are 2 catalitic converters, so 1 sensor for each. Godd Luck and keep us posted!
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Junior User
Joined: Jul 2003
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From: Shawnee KS
O2 sensor questions
AUGH!! So this is really going to be fun huh? It sounds like then if I'm getting the code for the #2, then it should be the driver's side sensor. Guess I'll go with that first and see what happens. That is unless I hear otherwise from someone else. I'll let you know what happens! Thanks VERY much to all! I'm sooooo glad I found this board!
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Hotshot
Joined: Aug 2002
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From: BC, Canada
O2 sensor questions
Ford figures that the O2's are really easy to replace. Warranty pays .5 hr to replace either one or .8 to replace both. Aren't they generous? 
O2 11 is passenger side front (1st one on bank one)
O2 12 is 2nd on bank one (behind the cat)
O2 21 is bank 2, first one
O2 22 is bank 2, 2nd one.
Is that as clear as mud?
O2 11 is passenger side front (1st one on bank one)
O2 12 is 2nd on bank one (behind the cat)
O2 21 is bank 2, first one
O2 22 is bank 2, 2nd one.
Is that as clear as mud?
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Junior User
Joined: Jul 2003
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From: Shawnee KS
O2 sensor questions
OK ya'll ain't kidding! What type and size of wrench do I need to get that thing off with? Will a regular wrench work or do I need a special 90 degree wrench or something? I've got the tire off now and I'm working on the passenger side sensor. Any help (and quickly please) is appreciated!!
Postmaster
Joined: May 2002
Posts: 3,028
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From: Annapolis, Maryland
O2 sensor questions
Originally posted by boxdoc2
OK ya'll ain't kidding! What type and size of wrench do I need to get that thing off with? Will a regular wrench work or do I need a special 90 degree wrench or something? I've got the tire off now and I'm working on the passenger side sensor. Any help (and quickly please) is appreciated!!
OK ya'll ain't kidding! What type and size of wrench do I need to get that thing off with? Will a regular wrench work or do I need a special 90 degree wrench or something? I've got the tire off now and I'm working on the passenger side sensor. Any help (and quickly please) is appreciated!!
The tube is kind of a pain to extract as well, but it will come out!
Let me know if you need any more help!
XXL
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Junior User
Joined: Jul 2003
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From: Shawnee KS
O2 sensor questions
I jacked with it for quite awhile, but couldn't get it done this time. I did everthing you told me and I just couldn't get anything in there to losen the sensor. It's like it was just welded in there! I didn't have a 7/8(?) wrench and the only ones I could find looked like they would have been way too long to reach in the space. I also had a heat shield that was really ticking me off to! Any suggestions on how to get that thing loose? I mean, even the ones post-cat conv. were pretty solid. Thanks again!!
Postmaster
Joined: May 2002
Posts: 3,028
Likes: 1
From: Annapolis, Maryland
O2 sensor questions
Originally posted by boxdoc2
I jacked with it for quite awhile, but couldn't get it done this time. I did everthing you told me and I just couldn't get anything in there to losen the sensor. It's like it was just welded in there! I didn't have a 7/8(?) wrench and the only ones I could find looked like they would have been way too long to reach in the space. I also had a heat shield that was really ticking me off to! Any suggestions on how to get that thing loose? I mean, even the ones post-cat conv. were pretty solid. Thanks again!!
I jacked with it for quite awhile, but couldn't get it done this time. I did everthing you told me and I just couldn't get anything in there to losen the sensor. It's like it was just welded in there! I didn't have a 7/8(?) wrench and the only ones I could find looked like they would have been way too long to reach in the space. I also had a heat shield that was really ticking me off to! Any suggestions on how to get that thing loose? I mean, even the ones post-cat conv. were pretty solid. Thanks again!!
I forgot to add in my last post that I cut the wires on the old O2 sensor so they wouldn't twist up and keep me from unscrewing it. After I removed the sensor, I used a screwdriver to push the little tab on the connection and the old, cut connection fell out.
XXL