Help replacing 02 sensor - '86 300E
 

I jacked my car up last night and removed the underbody panel to have a peek. I honestly can't find the oxygen sensor... where is it?
I have a replacement Bosch part, so I at least know what one looks like. And I have a special socket tool that should allow me to get a wrench on it... but I need to find it before I can replace it. Any help?
Also, are there any tricks I need be aware of, or is it just plug and play?
FYI - the check engine light is NOT illuminated. However, a mechanic told me that the output of the existing sensor is frozen at .7V.
Thanks guys!
Mika

The sensor should be just in front of the catalytic converter on the exhaust pipe, you're looking a bit too far to the front.

It's just ahead of the converter inlet on the top side of the pipe, surrounded by a heat shield.

Unless you have failed an emission inspection or you've noticed an increase in fuel consumption or are having driveability problems when the engine is at operating temperature I question whether it needs to be replaced.

You can eavesdrop on the 02 sensor output wave form by removing the pass. side carpet. Underneath you will notice a single wire connector and a two wire connector. The former is the O2 sensor output and the latter is the O2 sensor heater. Pull the single wire connector out just enough to get a small scope test lead on the pin and connect the other scope lead to ground. This allows you to view the wave form without distrurbing the circuit.

At idle the O2 sensor should quickly jump back and forth between about .2 and .8 volts about once per second.

You should also disconnect the heater connector and check that the harness has system voltage and the sensor heater itself shows continuity.

Duke

So it is located near the middle of the car where there two exhausts join?
Do I need to remove any part of the exhaust system to get to it?
Thanks for your reply!
Mika

yes, between where the two pipes merge and the converter. its sits on top, rising vertically. You need special socket to remove. It'll be in there real tight, believe me. best to apply lots of liquid wrench or equivalent, let it sit for some time.

Many have had to either rap on pipe to vibrate the rust off the threads or apply heat with a small torch to loosen.

Thanks! Is it best to remove the center exhaust pipe section, or can I get to it without taking the exhaust apart?
Mika

You can get it out w/o taking the exhaust down. I just used some Liquid Wrench-type stuff, let it soak a bit, then I used an adjustable wrench and a breaker bar to get it unthreaded.

Go for a short drive so the pipe is a little heated before you start. Helps in removal.