PDA

View Full Version : How-To: Replace primary O2 sensor on Gen 1 MS3



shift8
04-22-2014, 11:21 AM
In one of my recent posts, I noted that I had the P2177 and P2097 codes (http://www.torontomazda3.ca/forum/showthread.php?75241-Ran-into-P2177-and-P2097-tonight). After much research and cleaning the MAF, I came to the conclusion I was likely going to require a new sensor. The suggestion from MajesticBlueNTO was nice as the sensor from Rock Auto was quite a bit cheaper, even with shipping. It just took hella long time to get here, but no biggie as I work from home, so I just parked the car.

Since this was the first time I've replaced one of these sensors, I decided to take some pictures along the way. Doing it myself was not all that difficult, save for getting the damn sensor out, and accessing the wiring harness under the car. Any suggestions on anything I did wrong or could have made this easier are welcome.

First, I'm replacing the primary O2 sensor, closest to the front. This sensor has 2 connectors located under the car.

Before you start: Use something like PB Blaster or (in my case because I had access to it), Liquid Wrench penetrating oil. WD40 will do nothing. You need to spray the O2 sensor liberally and let it sit anywhere from a few minutes, to a day. I tried removing the O2 sensor without doing this, and it was impossible. Once I sprayed the Liquid Wrench and let it sit overnight, the sensor came out with very little force. If you're changing this sensor, you likely have 125,000km or more and the sensor will be fairly corroded.

Tools I Used
* 11mm socket (to remove the battery connector)
* 1/2" drive, 7/8" oxygen sensor socket (http://www.canadiantire.ca/en/pdp/oxygen-sensor-socket-bit-0256298p.html)
* 1/2" drive wrench with extension, and/or universal joint (I used a breaker bar since it had a built in universal joint/swivel head)
* Liquid Wrench Penetrating Oil (http://www.liquidwrench.com/products/#!/4) or PB Blaster (http://www.canadiantire.ca/en/pdp/pb-blaster-0381510p.htm)
* Jack and stands

Process
(Larger images available in the album on imgur at http://imgur.com/a/lA7k3)

The location of the sensor is shown in the next 2 pictures:

http://i.imgur.com/4NGJ69Ul.jpg

http://i.imgur.com/Uo256NNl.jpg

First I disconnected the negative terminal of the battery:

http://i.imgur.com/35dicy6l.jpg

Then I put the cover back on and lay the cable on top so it doesn't touch anything:

http://i.imgur.com/L9Ep1Mgl.jpg

At this point I decided to follow the cable and find out where the connectors were. Under the car. Neat! Access was pretty easy overall once I jacked the car up and got under there. In the following pictures, front of the car is to the upper-left corner of the frame. I took a wider angle picture so you can see the connectors in relation to the rear motor mount; just above it and towards the front.

http://i.imgur.com/YshTdhal.jpg

http://i.imgur.com/DnbdksBl.jpg

I decided to make sure I was going to be able to access and get the connectors undone before removing the O2 sensor. This part was a bit of a pain due to the lack of space around the connectors. You could pretty much only access the connectors with one hand. For the larger connector (the black one) I was able to use a small screwdriver just as a lever to press down on the release tab. While applying pressure down I also pushed towards the rear of the car. After a couple tries the connector came off without too much issue.

The second connector, the smaller grey one, was a pain in the butt. On the first connector the release tab is attached to the harness itself, so you're applying pressure on the part you're trying to remove. On the small grey connector, the release tab is on the harness that the grey connector plugs into. I tried everything I could to get the connector out of the harness with one hand, but I simply couldn't. Getting 2 hands in there was incredibly difficult, but I finally figured out a method that worked for me.

If you have large hands, this is not going to work for you. Luckily in this case I had just enough room to maneuver so that I could get one hand in to press the release tab, and another to pull on the connector. Here is how I did it:

http://i.imgur.com/y78cNb1l.jpg

The image is mirrored actually. On the right side of the picture, I was grasping the grey connector. On the left side, my index finger was pressing in the release tab. The only way I could access with both hands was this crossover method.

Here are the 2 connectors once I got them released:

http://i.imgur.com/zeCLEQjl.jpg

After that, everything else was pretty straight forward. There is a little pressure tab thing (like on the cables on the battery box) where you need a small pair of needle nose pliers to squeeze and release. Then going back up to the engine bay, there are 2 wiring harnesses that look like paperclips. Just lift the cable out of those 2 clips (I found it easier to do the one at the bottom while I was still under the car). The last one is up close to the O2 sensor itself and is a pigtail shaped harness. Just take the cable and go clockwise with the cable hanging out to the side of the harness. You can then pull the cable back up from under the car.

At this point, use the oxygen sensor socket to remove the O2 sensor. It should come out pretty easily. If not, you might need to spray with penetrating oil again and let it sit for a bit. Also, you probably want to put something under the car to catch the dripping oil as I put a small divet in my asphalt from the drips that sat there overnight.

After that, read the O2 sensor installation instructions. I had the M12 sensor which said to install at 13-17 ft/lbs of torque, or 3/4 to 1 full turn. My torque wrench only went as low as 20 ft/lbs torque, so I installed via 3/4 turn (after finger tight).

Run the cable down back under the car in the reverse order. Install the cable via the pigtail by running the cable between the wires in a counterclockwise direction, clip into the upper clip behind the engine, go under the car, clip into the 2nd lower clip, then plug in your harnesses, grey first, then black. Don't forget to also plug the pressure clip back into the hole as well.

After that, re-attach the battery negative terminal and start'r up!

loki
04-22-2014, 11:26 AM
the key to a successful O2 sensor removal without stripping it is a good O2 socket. I have one that will grab the sensor on all sides with just the slit for the wire

shift8
04-22-2014, 11:28 AM
the key to a successful O2 sensor removal without stripping it is a good O2 socket. I have one that will grab the sensor on all sides with just the slit for the wire

Oh I hadn't seen one of those. Mine only had 5 sides instead of all six. For me the trick was patience with penetrating oil. After that, very little pressure was needed.

loki
04-22-2014, 11:30 AM
Oh I hadn't seen one of those. Mine only had 5 sides instead of all six. For me the trick was patience with penetrating oil. After that, very little pressure was needed.

I'll post up pics of mine later

and boyracer can tell everyone where to pick one up, but with gripping each side, it's almost impossible for it to slip causing the edges to get rounded

Mr Wilson
04-22-2014, 11:32 AM
the key to a successful O2 sensor removal without stripping it is a good O2 socket. I have one that will grab the sensor on all sides with just the slit for the wire

Pffft the secret is breakfasteatre

bubba1983
04-22-2014, 01:11 PM
or, cut the wire, use a deep socket and an impact....and no gloves...

DamagedGoods
04-22-2014, 01:36 PM
http://img.tapatalk.com/d/14/04/23/egage4u9.jpg

This is the style I like, and I think its the same one Loki was referring to. Came in handy when doing a downpipe this weekend, the other style was flexing so much you could see it expand.

boyracer
04-22-2014, 03:07 PM
I'll post up pics of mine later

and boyracer can tell everyone where to pick one up, but with gripping each side, it's almost impossible for it to slip causing the edges to get rounded

Canadian Tire is where I picked them up

jay93
04-29-2014, 01:19 AM
leifmadsen pretty.funny running into this thread as we were talking about this tonight at massiv

shift8
04-29-2014, 09:21 AM
Haha this is the thread I wrote in relation to our discussion at MASIV. Hadn't seen any simple docs for this so used my tech writing skills to write it down.