I am assuming they ran two tests.

Was the engine hot (enough)?
My 260E would always fail the first test, but would pass once the engine got nice and hot.

Did you add anything to the fuel beforehand?
Fuel additives will elevate HC readings.

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2008 E350 4matic / Black/Anthracite

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Gone but not Forgotten:
2001 E430 4matic, 206,xxx miles, Black/Charcoal
1995 E320, 252,xxx miles, Black/Grey
1989 260E, 223,00 miles, Black/Black