O2 Sensor Wrench
 

Looks like I'm faced with replacing pre-convertor O2 sensor on '97 E320. Keep getting code P0133. Haven't looked for sensor yet but can it be loosened with crows foot wrench on a 3/8 inch drive? If so what size? Do I do it from top or from under car? TIA

Okay, I know ...
 

that I have to go under the car to replace the sensor. But I don't know how much clearance there is or what tools can be used to remove the sensor. Can anybody help me? TIA

You will need a special deep well socket that is uniquely designed to remove oxygen sensors. It can be purchased at any neighborhood auto parts store. Often the threads of the old sensor will lock up and seize and if you force the sensor you will strip the threads of the manifold or exhaust component. Pre-soak the old sensor in PB blaster for hours ahead of time and continue with the blaster while removing the sensor. Use off and on motion with your ratchet so that the threads do not seize up...all the while continue to spray with PB blaster.

If the threads do get messed up even after above procedure then pick up a thread chaser at same auto parts store (usually 18 mm X 1.5) and crank that through the threads on the exhaust piece. Make sure the trace tool is aligned properly with the threaded hole... DO NOT CROSS THREAD. Install the new sensor... clear the old code and you are finished.

Suggest you drive car up on some sort of ramp to give yourself working clearance.

okc329, auto stores sell the crow's foot wrench for oxygen sensor removal/installation ... it has a slot for the connector wire to pass through. Typically new oxygen sensors have never-seize on the threads to make future removal easier. The one on our 1991 300CE loosened easily even though I've read horror stories about the difficulty removing them. Try removing the oxygen sensor as-is. If the threads seem rusted then apply a rust cutter and let it sit for a while. Be sure to use never-seize on the threads of the new oxygen sensor if they are not already coated.

A packet of never seize will come with the new oxygen sensor. Carefully apply paste to new sensor's threads only.

To date I've always gotten by without the special socket by threading the pigtail connector through a 7/8" box end wrench and using the wrench to remove the sensor.

you can also rent the tool from autozone/ advance autoparts and return it after you are done. bassicly you buy it, use it and return it for a full refund....thay call it lend-a-tool program or something....i have done it multiple times.......

Thanks so far ...
 

Today I purchased the O2 sensor socket wrench. The socket is 3 1/2 inches long and can be driven with 1" box wrench or 3/8" rachet. Is anybody familiar enough with the underside of a '97 E320 to tell me if there is enough clearance for the socket and rachet or box wrench?

Lucky you :) I was there as my indy struggled 30 minutes trying to remove the O2 sendor, standing under the raised car, with the right wrench of course.

My mom has a 98 E320, and my dad was going to replace to Oxygen sensor, is it located somewhere near the exhaust? I'm asking here for him. Thanks...

Yes, access is under the car along the exhaust pipes. Looks like your car has 4 different o2 sensors, 2 ahead of catalytic converter on left and right and 2 after the converter left and right. You need an OBD reader to tell which one may be out. Find the part with the online parts seller FastLane. I would suggest going with the more expensive version that has the correct length wire versus the universal sensor where you need to splice the new sensor to the old plug. IMO the splice mechanism is not well designed and was not easy to do. If you have an ATF leak in the vicinity of this splice, the ATF will eventually worm its way into the connection and the splice will fail. YMMV.

glenmore
1991 300CE
2000 C280