The O2 sensor before the TWC on by 95 S320 failed this summer. I considered changing it myself before I found it was covered under the emissions warranty. I asked the dealer how tough it was to change and he made it sound fairly easy. He suggested getting the right wrench and mentioned that sometimes you have to put a torch on the fitting to get it loose.

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Tom Savage
Vienna, WV
1984 300D Euro
1995 S320