2002 Toyota Corolla
How to replace your Oxygen (O2) Sensors
My wife's corolla is getting old. It's starting to show signs of wear and tear from th daily commute and child hauling. Most recently, the
check engine light came on and the car started running poorly. Now, any time a check engine light comes on I stop by Autozone. They'll read
the car's computer and pull the trouble code as well as likely culprits for you. It's an extremely useful free service. After getting the codes
pulled I determined that the most likely culprit was the O2 sensors.
New O2 sensors for this car are very expensive! It was over $200.00 (usd)! But that being said, after doing this job I realized that it would
be triple to quadruple the cost to have a shop change them out for you. Read on to find out why.
Please, before you start on this, remember to disconnect the negative battery cable.
This image is of the area between the back of the engine and firewall. Dead center in the image is the Oxygen Sensor protruding from the
exhaust manifold. It has a plate with two bolts that hold it in place.
Here's the forward Oxygen sensor. It also comes with a gasket to go between it and the exhaust manifold.
Once you remove the two bolts and disconnect the electrical connection you can remove and examine the Oxygen sensor. As you can see, this one
has seen a lot of heat and exhaust gasses over the years. That explains the discoloration.
In terms of extracting the Oxygen sensor I found it is most easily removed with a stubby socket wrench and a deep socket. The bolts holding it
in place are 12mm bolts. Reinstallation is simple, place the bolts through the new oxygen sensor, put the gasket on the bolts, press the assembly in
place, and torque down the bolts. Once it's bolted in you can connect the electrical connector and you are done with the front Oxygen Sensor!
This culprit is the second Oxygen sensor. This was added to the Corolla about 1/2 way through it's production run over the years. Because it was
added later, I don't believe the maintenance aspect of it's installation process was well thought out.
Here's where the fun begins. While the O2 Sensor itself is easy to get to by jacking up the car, disconnecting it from the wiring harness is a
completely different story. You start by removing the passenger seat. (I'm adding a note here, a reader came up with an alternate means of
disconnecting the second O2 sensor. His method doesn't require removing everything, but I did try a similar process originally and couldn't get
far enough into the car. You may want to look at Paul's comments at the end of the article, and if that fails, come back and follow this process.
The front two bolts are fairly easy to get to. They can be removed with a 14mm wrench. On some cars, depending on the trim lvel these may be
covered with decorative plastic.
The rear two bolts are also 14mm, and are most easily accessed from the back seat. Once you have all four bolts out, fold forward the seat back
and lift/twist the seat out of the car.
Now, here's the fun part. All the manuals and tech notes I have on hand say that all you have to do it remove the seat. In looking at the floor
there's obviously nothing there you can work with, so we have more disassembly to do. The center console comes next. There are two #2 Phillips head
screws at the front that need to be removed. You'll note the interesting patina from years of spilling starbucks down the side of the center
There's a small piece of interior fabric at the bottom of the storage bin at the back of the console. Lift up the fabric and you'll find two
bolts underneath. If I remember correctly they are 10mm. Unbolt them.
Finally you need to pop loose the escutcheon ring that goes around the shifter area. Pry it up from the top side. I spun it 90 degrees to get it
out of the way.
With everything disconnected lift the center console up and over the emergency brake towards the front of the car. Set it aside for now. You
may get temporarily excited about seeing the exposed wiring harness, but I assure you, that's not part of what we're digging for.
After levering out the carpet from underneath the remaining section of the center console and doing some digging you'll find the connector.
There is just enough slack in the wiring to allow you to pull it up and expose it. Now, at this point I thought I'd struck gold.
I disconnected the wiring and slid under the car to pull it out from the body. The wire came loose a couple inches only to determine that the
ducting that's hidden underneath the carpet (for the rear vents) was laid on top of the harness wiring. The harness connector was just big enough
that it would not slide out between the body and the vent. More disassembly is required.
The trick is to loosen as much of the carpet as possible. Remove the plastic retaining clip from the front inner corner of the carpet.
Remove the door sill plastic trim. You'll want to pry this up carefully as it's held down by plastic clips that become brittle with age. If you
do break any, your local Ace hardware store will carry suitable replacements.
Remove the front kick panel. There's a black plastic screw on fastener that holds it in place. Unscrew it and pop the part loose then set it aside.
These goofy plastic pieces also need to be removed. If you can see the inside section there's a slot in the bottom that allows you to rotate it
~20 degrees to life the piece out.
Now with the extra pieces removed we can pry up the carpet. You'll see the black plastic vent I mentioned earlier. Grab the connector for the O2
Sensor and shove it under the vent. With the carpet raised up there should be enough flex to do so.
Now it's time to get back under the car again. Please make sure that you properly support the car with stands! Now that the wiring has been appropriately
loosened from the inside you can pull the rubber boot out of the body and remove the wiring.
Here you can see the discolored Oxygen sensor after removal. The O2 Sensor requires a 22mm wrench to remove it from the exhaust pipe.
Here you see the new O2 sensor tightened down into the exhaust pipe and the wiring pushed through into the body. Seat the rubber boot correctly
and then you can lower the car. try to push the wiring through as far as possible from underneath.
From here, it's a matter of repeating the steps in reverse. Fish the wiring through under the vent and connect the new O2 Sensor, Put the carpet and
trim back in place. Reinstall the center console and the seat. Finally, reconnect the negative terminal on the battery.
You're done! Take the car for a test drive. You should note that it runs much better and the check engine light does not turn back on again.
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