I understand that a bad O2 sensor can destroy the CAT. Is there anything that can destroy the O2 Sensor - bad fuel pump, etc.? Keep going back to the beginning. I am trying to trace the steps why an O2 sensor failed. I recently replaced the CAT a month ago. Then the power stage went a week later. I understand that can damage a CAT.

So now I have to wonder if the new CAT has been destroyed by the power stage. I see no point in constantly replacing all these parts, of there is something killing them that I am unaware of or should be looking at. I a starting to learn that asking why something fails is very important. Far too often, I am learning, that the quick advice I am getting on replacing these parts has not at all been thought out very carefully. Now I am back at square one again with having to replace these things twice - Thank you. Bruce

About the only thing that can kill a cat is leaded gas. There are things that can shorten the life of the cat - basically, they are all related to running rich. A bad O2 sensor, FPR, leaky injector, etc... can all cause rich running, and this essentially "uses up" the cat faster than normal. But we're typically talking years before your cat would be ruined.

As the other poster mentioned, silicone can kill an O2 sensor. But running rich, burning oil, etc... only shorten the life, they do not suddenly destroy the sensor.

Your cat and O2 sensor should be fine if you've only had problems for a few weeks or a month, or even longer.

Keep learning and asking questions on the board. As you understand more about the various systems on the car, you'll figure out how they interrelate. I never knew about the airbox thermostat until I read about it on the board - I didn't even know it existed. If you don't know about this part, its a small thermostatic actuator (that costs a few $) that, when it fails, can fry your $300 Air Mass Meter! My brother replaced two AMMs on his 240 before I informed him of this! It just takes some time, but since I've surfed this board for the past 6 years, I can now tackle just about any repair that doesn't need a hydraulic press or a blowtorch!

Bruce,

An O2 sensor can fail due to:

1. Age

2. Being clogged up, due to running rich or burning oil. This is where other parts may indirectly cause the demise of the O2 sensor.

3. Contamination. Silicone is one known O2 sensor killer, never use silicone based lubes or sealants near the intake.

A catalytic converter can fail due to:

1. Age

2. Mechanical failure - the core breaks up, usually clogging the exhaust system.

3. Being clogged up, due to running rich or burning oil. A failed O2 sensor may cause the car to run rich, and clog up the cat.

4. Contamination. Leaded fuel will kill a catalytic converter. Besides the airport, I don't think you can buy leaded fuel anymore.

If a failed ignition power stage caused the car to "miss", rather than just completely die, enough raw fuel may have been dumped into to the exhaust to clog or burn up the O2 sensor or catalytic converter.

Other parts that may cause the car to run rich are the temperature sensor, worn/dirty/leaky fuel injectors, the fuel pressure regulator, the AMM or the ECU. The Bentley manual has instructions for testing those parts. Also, check for electrical problems (corrosion, loose contact) at the AMM, ECU, fuse box, underhood main FI fuse (near the power steering reservoir on the fender), and everywhere else.

I don't think there is any way a bad fuel pump could damage the O2 sensor.

Hope this helps!