Check fuses on passenger side by modules in engine bay. I had somewhat same problem on my 98 E320 scanner would't communicate the fuse was blown but CEL would light up. Hope this helps you out.

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1995 E320
1998 E320
1999 E320 4Matic
2000 E320 4Matic
2000 ML320
2007 C230 Sport
2003 Cadillac CTS