My folks have a 2001 or 2002 S500 sedan that left them stranded by the side of the road yesterday. The car has about 70k on it now; we bought it new back in the day.

The check engine light has come on a couple of times in the last three months. The first time the dealer put in a new MAF unit. Just last week the CEL/MIL came on again, and they diagnosed that it needed new O2 sensors, so those were replaced.

Yesterday on a 1000-mile highway trip, the car suddenly started to stumble badly and lose power. Before my dad gave up, the car was going 25mph down the highway with a wide open throttle. He shut her down and had to be towed over 130 miles backwards to the nearest dealership.

This morning that dealer diagnosed a "complete catalytic converter failure," and had to order parts. Dad threw him the keys and rented a car to continue on the trip today. My best guess is that something was wrong with the replacement O2-sensor from last week's repair, and way too much gas got dumped into the cat -- ultimately burning it up. I'm still surprised that pretty much ground the car to a complete halt, though.

Any other theories? It looks like M-B is going to eat at least some of the repair, despite the car being out of warranty. Just wanted to hear ideas from you experts.

Cheers, John

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'98 E300TD (W210) | Sold 6/09 with 205k and counting
'04 VW Touareg V10TDI