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Old 11-12-2010, 08:16 PM   #1 (permalink)
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How to replace 2001 Pre-Cat Oxygen Sensor

Hi all, my MDX has about 135k miles on it, and the gas mileage is down. One of the steps that I'm taking to try to get it higher is to replace the pre-cat O2 sensor. Many think that as long as they don't throw codes O2 sensors are fine, but I've found that's not the case. As the porous ceramic ages, it gets plugged and the response magnatude is reduced. You can google around to find more on it, but anyway, lazy O2 sensors can effect gas mileage.

Anyway, I'm not too happy with Acura right now. Despite the fact that there it tons of space under the hood of the 01 MDX, it is anything but serviceable. (FWIW, I have an 02 Mini Cooper S, and even though it's one of the smallest cars sold in the US, it is MUCH more serviceable...)

So, here are the basic steps:

1) Undo the 12mm bolt that holds the bracket where the O2 sensor connector is mounted.

2) Undo the 10mm bolt that holds some plastic cover thinggy above the connector bracket.

Now there is enough play to actually get to the tab that holds the connector on the bracket (the engineer who spec'ed that the sensor end of the connector should be mounted to the bracket should be shot! Or at least sent back to school....)

3) Wrestle with the bracket till you can get to the tab on the sensor end of the connector. Press it so that you can slide the assembled connector off the bracket.

4) Now you can get the connector someplace to where you can actually press the tab on the ECU side of the connetor to get the two halves apart.

5) Under the car (I used ramps to get space to work), you can either screw with the brain-dead of a design of the wire retainers, or if you get pisssed and impatient like I did just cut the wires at the sensor. (The upper one may be more accessable from above. After a while, I just gave up and cut the suckers.)

6) a 22mm wrench can then be used to undo the sensor. If you cut the wires, you can use a box end wrench. Some find that they need some penetrating oil here, but I didn't. My old sensor came free pretty easily.

7) Use some anti-sieze on the threads of the new sensor (not too much, get this stuff on the sensor element and you can mess up the sensor, then you have to do it all over again!) and mount it onto the exhaust pipe. Be carefull to not twist the wires too much as you do this. Screwing up the wires by not paying attention to this is a common rookie mistake.

8) Route the back up to the connector. Use the factory wire retainers if possible, or use wireties to make sure that the wiring is out of harms way.

9) Re-connect the two halves of the connector.

10) mount the connector back onto the bracket.

11) re-attach the two bolts (10mm and 12mm) and torque them down.

12) Drive and see how it goes!

I'll report later (after a couple of tanks of gas) if it made any difference. And I'll add some photos later. Right now I've got to go nurse my wounds (sharp plastic scratched up the back of my hand and wrist.)

Overall, what should have been a 20 min job was much longer due to the pisss poor design for servicability from Acura.

Matt

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Old 10-26-2012, 02:16 PM   #2 (permalink)
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O2 Sensor Connector Location 2002 MDX

The post by MattR is very helpful. I found the Bank 1 Sensor 1 in before the cat. I am unable to follow the wire to find where the connector plugs in. Is it located about 6" to the right of the dip-stick (standing in front of car)? Is so, that cable seems to be wrapped in with many other cables as it fades from view. Perhaps I have the wrong connector identified, as I cannot find any posts addressing this isssue. I don't want to snip any wires if I can avoid it. Any help here?
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Old 11-20-2012, 06:27 PM   #3 (permalink)
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Oxygen Sensor Wires / Connector Plug

Does anyone have any thoughts on my post from last month? Is it typical for the O2 Sensor wires to be taped or run through a tube with other wires? All the posts make this replacement sound so simple once the sensor is removed form the exhaust. I've got that part covered, but I cannot follow the wires through the engine bay. I'm considering just cutting all wires 6-8" from the new and existing sensors, and splicing in the new wires to the existing ones. I'm open to any suggestions, including proof of my ignorance. Thanks.

P.S. My '02 just passed 200,000 miles.
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Old 11-21-2012, 09:56 AM   #4 (permalink)
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Originally Posted by Keigle View Post
Does anyone have any thoughts on my post from last month? Is it typical for the O2 Sensor wires to be taped or run through a tube with other wires? All the posts make this replacement sound so simple once the sensor is removed form the exhaust. I've got that part covered, but I cannot follow the wires through the engine bay. I'm considering just cutting all wires 6-8" from the new and existing sensors, and splicing in the new wires to the existing ones. I'm open to any suggestions, including proof of my ignorance. Thanks.

P.S. My '02 just passed 200,000 miles.
I'm not sure if your 2002 MDX is similar to my 2001 MDX. I posted a picture of where my connector is located. Click >> HERE
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Old 11-21-2012, 04:15 PM   #5 (permalink)
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O2 Sensor Replacement

Tremendous help pvcMDX! The pictures and notes were incredibly useful. The trickiest part for me was getting the two halves of the connectors separated. I could not get enough grip from under the hood while my son pulled the wire from beneath the car. I ultimately reached under the connectors, pressed in the tab that releases the metal bracket, and wrestled them off the bracket. I was then able to grab both halves of the connectors to separate them while pressing the top connector tab. I also tied a 6' string to the old connector plug before I pulled the old O2 sensor out from underneath the car. I then tied that string to the new connector after I screwed in the new sensor, and was able to pull it up through the engine area from under the hood.

The new sensor is installed, P1035 code cleared and the Check Engine and VTM-4 lights are staying off. I'm looking forward to an improvement the mileage and a working VTM-4. Thanks again for the great help.
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Old 11-21-2012, 06:50 PM   #6 (permalink)
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Originally Posted by Keigle View Post
Tremendous help pvcMDX! The pictures and notes were incredibly useful.
What Brand/Part number O2 sensor did you use? I'm still throwing a P0135 OBD code after I replaced mine.
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Old 11-22-2012, 10:56 AM   #7 (permalink)
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Quote:
Originally Posted by pvcMDX View Post
I'm not sure if your 2002 MDX is similar to my 2001 MDX. I posted a picture of where my connector is located. Click >> HERE
Hmmmm; In this forum it seems that I lost the ability to edit my posts after one day. I made a better version of my instructions and pictures so I am posting this second link. Please ignore the link I posted above to the old instructions and pictures. Here's the new link:

I posted a picture of where my connector is located. Click >> HERE

I have asked the Admin to delete the old thread.
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Old 11-22-2012, 06:07 PM   #8 (permalink)
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Originally Posted by pvcMDX View Post
What Brand/Part number O2 sensor did you use? I'm still throwing a P0135 OBD code after I replaced mine.
I used a Delphi ES20114 Sensor. I bought it from Amazon for about $50.
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Old 11-02-2014, 03:55 PM   #9 (permalink)
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Got the infamous P0135, changed with universal Bosch sensor (pre-cat). Got the codes cleared and then CEL and VTM light come back on almost right away. Drove around hwy and city for a good 2 hours solid. Re-checked the codes again and still P0135. Cleared the code and again lights back on almost instantly. Anyone else had this problem? I would really hate to have to take this to the dealership. Our MDX is a 2001.
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