I'm tring to figure out how to check out why the CEL is on in my 1988 300 SEL. I've found a couple different threads that are helpful but the lingo is tough. What do DTC and ECU mean? Thanks.
eric

Somewhere there is a thread on Mercedes abbreviations. I don’t know if the ones you are looking for are in it but you should check it out anyway.

Diagnostic Trouble Code
Engine Control Unit

Here's a few more you may find helpful.
POS
SOB
WTF

"GD" may be used in conjunction with any of the above, depending on the level of difficulty of the job at hand.

Oh, I almost forgot. Check your O2 sensor.