I had an issue with my daughters 2000 Mercedes Benz SLK230. It had no power. Did some checks and the compressor valve (think waste gate in a turbo) wasnt closing. Many owners have wasted lost of money trying to resolve the issue - there is often several error codes.
The fix is rediculously simple. Inside the power distribution case on the left side ubder the bonnet is a black box full of relays. Remove it and take the cover off and check for dry joints. Solder any dry joints, out it back in and your car will be transformed.
Btw the compressor valve is over $700. I've read of people replacing it and the ECU, and the relay board costing thousands. The trouble is oeople dont repair anymore - they replace.
Jim