How to replace 2001 Pre-Cat Oxygen Sensor - Acura MDX Forum : Acura MDX SUV Forums
 
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post #1 of 13 (permalink) Old 11-12-2010, 08:16 PM Thread Starter
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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

12)


2001 MDX Touring
2002 Mini Cooper S
1965 Mustang Convertible

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post #2 of 13 (permalink) Old 10-26-2012, 02:16 PM
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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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post #3 of 13 (permalink) Old 11-20-2012, 06:27 PM
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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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post #4 of 13 (permalink) Old 11-21-2012, 09:56 AM
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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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post #5 of 13 (permalink) Old 11-21-2012, 04:15 PM
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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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post #6 of 13 (permalink) Old 11-21-2012, 06:50 PM
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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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post #7 of 13 (permalink) Old 11-22-2012, 10:56 AM
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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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post #8 of 13 (permalink) Old 11-22-2012, 06:07 PM
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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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post #9 of 13 (permalink) Old 11-02-2014, 03:55 PM
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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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post #10 of 13 (permalink) Old 09-15-2015, 08:43 PM
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To help with step 3 concerning removing the connector plug (02 plug and the engine wiring harness plug) that is attached to the metal bracket is to use a screw driver from the top of the engine and slide it down to the outside of the OLD plug that is attached to the 02 sensor that you are replacing and break the outside plastic that is holding the sensor to the metal bracket. Once this is done you will be able to move to step 4
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post #11 of 13 (permalink) Old 10-18-2015, 06:06 PM
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FWIW, the post below concerns a 2004 MDX which is a little different. I just posted it here for those who are having trouble getting the connectors apart (I'd bet dollars to donuts the same process works on the 2001 MDX, based on the comments above).

Everyone (including me, just now) seems to have trouble getting the O2 sensor plugs undone. The trick is that they're not supposed to come apart until they're released from the metal "tab" that holds the female (car) side of the plug. You just need to run a thin screwdriver between the metal tab and the plastic connector, to release the tab that holds them together. This can be a little fiddly, but jam a small, flat screwdriver from the O2 sensor side of the plug, between the plug and the metal tab that holds it, and after a couple attempts you'll be able to pull the plugs off the tab together. Then just push down the obvious tab with your thumb and the male and female connectors will easily disengage. They just never, ever come apart while the female plug is still attached to the metal tab that holds it in place. But there's no reason to unbolt the metal tab (12mm bolts) or worse, break the plastic so it no longer stays in place on the mounting tab.

I'd sincerely recommend doing the front sensor first, so you can see how this works - the rear one is done mainly by feel, though I found it's not hard to bend the mounting tab back toward the firewall so you can see it better. Then it's really only a 5 minute job to swap out the rear O2 sensor (less for the front one).

I just swapped both of mine and the PCV valve this afternoon to see if I can get a little better gas mileage. I probably have a valve adjustment in my future too, once I hear back from the previous owner to find out if he ever did it or not.
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post #12 of 13 (permalink) Old 09-24-2016, 02:05 PM
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Thanks Matt and company for the post. It was very helpful.

I was successful after about 3 hours all told including a trip to home depot for a 22mm wrench and looking up this post! and lots of cussing!

I did a few things differently.

1) I removed the two pieces of the connector first, pulling UP on the part that you don't replace after pinching the side away from the bracket. I had spent about 30 minutes trying to pull the side that attaches to the O2 sensor down, not realizing that would never work with the bracket snapped in place to the bottom half.

2) Once I had the top half off, I used a long screw driver (and some WD40) and my finger from underneath, to push down on the O2 side connector pushing it away from the rusted locked metal bracket.

3) I was using a monkey wrench and a mallet underneath the car, I just drove up on a curb to give me enough room, and I was just stripping the O2 sensor. So I ended up clipping the wire so I could get a box end wrench over it. Even with the 22mm box end hitting it with a mallet wasn't working, so I took another long box end wrench, put it over the open end of the 22, made a 2 foot long lever arm and then slowly pushed the sensor free. Gotta remember tighty righty, but when you are upside down, righty might be loosey. The 22mm from home depot was like $6.50 vs. the fancy O2 wrench from a auto parts place at about $20?

4) After resetting the Codes using my cheapy OBD2 reader, no more P0135 code! and I can get my car emissions inspected, and I didn't pay about $1,000 for the dealer to do it. I also has another code P1739, suggested the 3rd clutch pressure switch, but after looking at this: P1739 ACURA Problem in 3rd Clutch Pressure Switch Circuit, I just filled up the transmission fluid, put maybe 1/2 a quart of honda transmission fluid in and that went away. My clue was that the VTM light would come on after a bit of driving and then sometimes go off. But eventually it stayed on. I added only about 4 ounces first, and it went out for like 2 seconds after you started the car it went back on, so that sounded to me like the fluid flew around and there wasn't enough to cover the sensor. Adding another maybe 6 ounces and that's gone too.

Happy MDXing - Mine is a 2001 - very first black MDX in the washington DC area with over 262.000 miles on it and I've done most of my own maintenance for the past 10 years. GREAT car..
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post #13 of 13 (permalink) Old 09-25-2016, 10:36 PM
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Quick tip on this... Run the vehicle until the exhaust is good and hot, then remove the o2 sensors. They will come out much easier, wear gloves to avoid getting burned.

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