Hi,

 

I'm looking at the Haynes Repair manual, but it only has a picture of the pre-cat oxygen sensor for the 1992-1998 model.

Does anyone know the precise location of the pre-cat oxygen sensor on the 1999-2002 Toyota Corolla?

I know it has to be somewhere between the exhaust manifold and the catalytic converter, but I can't seem to find it based on the book (and its too dark to go look at the car). Can anyone here point me in the right direction?

Would it be accessible from the top? Or would I have to jack the car up to access the pre-cat O2 sensor?

Thanks, and I appreciate your input.

Start at the exhaust manifold and follow the exhaust pipe down. The oxygen sensor is sticking out near the bottom of the car. I've found that the best way to get to it is from the top, but you should remove the exhaust manifold heat shield (6 12 mm bolts I believe). Be careful taking the bolts off, as they may be quite rusty. You will need a 10 mm socket or combination wrench to remove the oxygen sensor's retaining nuts.

Here's a picture of what you're looking for:

https://i838.photobucket.com/albums/zz308/teppista881/100_1769.jpg

Thanks dshadle1!

I don't know if its against forum rules, but I found a very informative link on how to change oxygen sensors on the 1999-2002 corollas.

http://www.theymightberacing.com/Maintenance/O2Sensors.aspx

Pretty informative, although you might be able to skip the part where he removes the seat and move it all the way back instead.

Thanks dshadle1!

 

I don't know if its against forum rules, but I found a very informative link on how to change oxygen sensors on the 1999-2002 corollas.

http://www.theymight.../O2Sensors.aspx

Pretty informative, although you might be able to skip the part where he removes the seat and move it all the way back instead.

That author says the nuts are 12 mm. I was just guessing at 10, since it has been a while since I got in there. Just try both, of course.

Start at the exhaust manifold and follow the exhaust pipe down. The oxygen sensor is sticking out near the bottom of the car. I've found that the best way to get to it is from the top, but you should remove the exhaust manifold heat shield (6 12 mm bolts I believe). Be careful taking the bolts off, as they may be quite rusty. You will need a 10 mm socket or combination wrench to remove the oxygen sensor's retaining nuts.

 

Here's a picture of what you're looking for:

http://i838.photobuc...81/100_1769.jpg

Boy is that exhaust manifold heat shield hard to get too!!!! You were right, there are 6 bolts. Mine were VERY rusted, especially on the exterior. I spent 2 hours getting that heat shield out (those two far down were the hardest to get too). I then spent another hour figuring out how to disconnect the O2 electrical connector. I don't have a picture yet, but apparently you can yank it out of the plastic retaining pin so that its easier to remove.

Now, I'll just remove the O2 sensor tomorrow, and do the reverse of what I did.

My back hurts from trying to reach over the middle-rear of the engine. It hurts......

Start at the exhaust manifold and follow the exhaust pipe down. The oxygen sensor is sticking out near the bottom of the car. I've found that the best way to get to it is from the top, but you should remove the exhaust manifold heat shield (6 12 mm bolts I believe). Be careful taking the bolts off, as they may be quite rusty. You will need a 10 mm socket or combination wrench to remove the oxygen sensor's retaining nuts.

Here's a picture of what you're looking for:

http://i838.photobuc...81/100_1769.jpg

Boy is that exhaust manifold heat shield hard to get too!!!! You were right, there are 6 bolts. Mine were VERY rusted, especially on the exterior. I spent 2 hours getting that heat shield out (those two far down were the hardest to get too). I then spent another hour figuring out how to disconnect the O2 electrical connector. I don't have a picture yet, but apparently you can yank it out of the plastic retaining pin so that its easier to remove.

Now, I'll just remove the O2 sensor tomorrow, and do the reverse of what I did.

My back hurts from trying to reach over the middle-rear of the engine. It hurts......

Yep. The shorter you are (or your arms), the worse it is. Very awkward place!

I desperately need help with this.

I unscrewed my O2 sensor, and its loose, but there's a bolt hanging from the above exhaust manifold there's blocking its removal. I'll let the pictures do the talking.

That's the pre-cat O2 sensor viewed from the top-down.

A closer-up view of the pre-cat O2 sensor. That spring-like thing in the center of the picture is what's blocking the removal of the O2 sensor.

Three separate views of the offending bolt/spring.

WHAT SHOULD I DO WITH THIS??? It is too close to the O2 sensor for a socket to fit over it. I don't have (on me at the moment) an open wrench set that is SHORT enough to fit into the constrained space. I'm not strong enough to compress that spring either.

Common problem. You might be able to get under the car and move the exhaust pipe over just enough to get the sensor and the backing plate out. To make it easier, maybe get a friend to reach down and grab it while you move the pipe. BE SURE you put the car on jack stands and rock it a few times to make sure it's sturdy, as you will be putting some sideways pressure on the pipe. The problem with that spring bolt is that without some crazy tools you will never be able to get enough torque on it to put it back in if you ever got it out. The saga continues...

PS. If you are small enough to reach your arm under the car to pull the pipe without jack stands that might work, too. You will definitely need a helper, though. Problem is the pipe is in the dead center of the vehicle--long arms needed!

Common problem. You might be able to get under the car and move the exhaust pipe over just enough to get the sensor and the backing plate out. To make it easier, maybe get a friend to reach down and grab it while you move the pipe. BE SURE you put the car on jack stands and rock it a few times to make sure it's sturdy, as you will be putting some sideways pressure on the pipe. The problem with that spring bolt is that without some crazy tools you will never be able to get enough torque on it to put it back in if you ever got it out. The saga continues...

 

PS. If you are small enough to reach your arm under the car to pull the pipe without jack stands that might work, too. You will definitely need a helper, though. Problem is the pipe is in the dead center of the vehicle--long arms needed!

I can't do that. The vertical bolt does not come off if the oxygen sensor is attached. If the vertical bolt does not come off, the exhaust pipe cannot be moved. Would using a clamp to compress that spring work?

I guess a better way to put it is..... how do I move the exhaust pipe if the bolt attaching the pipe to the exhaust manifold is still attached?

Common problem. You might be able to get under the car and move the exhaust pipe over just enough to get the sensor and the backing plate out. To make it easier, maybe get a friend to reach down and grab it while you move the pipe. BE SURE you put the car on jack stands and rock it a few times to make sure it's sturdy, as you will be putting some sideways pressure on the pipe. The problem with that spring bolt is that without some crazy tools you will never be able to get enough torque on it to put it back in if you ever got it out. The saga continues...

PS. If you are small enough to reach your arm under the car to pull the pipe without jack stands that might work, too. You will definitely need a helper, though. Problem is the pipe is in the dead center of the vehicle--long arms needed!

I can't do that. The vertical bolt does not come off if the oxygen sensor is attached. If the vertical bolt does not come off, the exhaust pipe cannot be moved. Would using a clamp to compress that spring work?

I guess a better way to put it is..... how do I move the exhaust pipe if the bolt attaching the pipe to the exhaust manifold is still attached?

It should move, just not much. The goal is to get it moved just enough to get the sensor off, not to get it completely out of the way, maybe a half inch. As I was trying to say, it will take some force to move the pipe, but think of it as "flexing," not relocating it.

It should move, just not much. The goal is to get it moved just enough to get the sensor off, not to get it completely out of the way, maybe a half inch. As I was trying to say, it will take some force to move the pipe, but think of it as "flexing," not relocating it.

I have no idea what I did. I tried yanking the O2 sensor out this morning and IT CAME OFF!!!!

Placebo or not, I think the cold weather shrunk the vertical bolt!! I placed in the new O2 sensor (w/o screwing it in yet) and am going to bed.

It should move, just not much. The goal is to get it moved just enough to get the sensor off, not to get it completely out of the way, maybe a half inch. As I was trying to say, it will take some force to move the pipe, but think of it as "flexing," not relocating it.

 

I have no idea what I did. I tried yanking the O2 sensor out this morning and IT CAME OFF!!!!

Placebo or not, I think the cold weather shrunk the vertical bolt!! I placed in the new O2 sensor (w/o screwing it in yet) and am going to bed.

Awesome!

Thanks dshandle! Greatly appreciate your input and help on this little project.

Should I be expecting white smoke and a burning smell from the new O2 sensor? (Hopefully its the seals burning in?)