I have a CEL on my 91 190E 2.6L, I was guessing with 109 on the clock it would be due for an 02 sensor but what else are you thinking of?

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1981 300TD
2005 C55
2004 E500
1999 ML430
1992 400E
1998 C43
2001 SL500
1988 300SEL
1986 190E 16V
1991 190E 2.6