If you determine that the ETA harness is the problem and you are good at soldering, you can order the 90-degree type ETA harness from Germany (at least you could back in 2007). It was part 140 540 15 81. I'm presuming your 92 has the 90-degree type harness connector.

Check out this post. O2 sensor electronics testing

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1993 400E, 256,000 miles (totaled)
1994 E420, 200,000+ miles
1995 E420, 201,000 miles