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.