Ditto the CPS. BUT, if you're unable to get a code to display with an illuminated CEL, it could be a bad computer (ECM). Rare but not impossible. It happened to a used car dealer friend who bought a C-Class. CEL lit, could pull no codes. It read there was a 'communication fault' on the reader. It was the computer. I hope that is not the case.
__________________ Be careful about reading health books. You may die of a misprint.- Mark Twain
Go to any M/B dealer and buy one. Why wait 3-5 days. The CPS is located under the hood where the engine and transmission meet. It is a bit of a pain to install and you will need a female torx socket #E8 to remove the only bolt. Here is a diagram of its location; it is more towards the driver's side.