Where is the diagnostic socket on my 2006 C180

I recommend that you take it to your local Mercedes mechanic to run an engine diagnostic test. It's not likely that you local auto parts store will be able to help you. You don't necessarily need to go to the dealer, since they normally charge the highest prices; however, my local dealership charges $125 for and engine diagnostic. I don't know what you consider expensive.

Your car is in 'get you home' mode. Get it to a gararge where they can plug in the diagnostics.

This could be the ecu control unit. Mercedes Ecm Repair
Sometimes a bad ecu will make a Mercedes misfire or not start. But the problem could also be related to a bad ignition key. You will need Star diagnostics to troubleshoot the vehicle.

auto diagnostic tool

Hi. Thanks for your question. For issues related to brake warning lights on dash illuminated for Mercedes C180, 1996 saloon. You can visit https://www.reliable-store.com and download the entire workshop manual which includes all the information along with the diagrams for better understanding. Good day!

this model from around this year is a dealer only diagnostic ,from the sound of it i think its time to trade it in quick before it starts eating a hole in your pocket money

The plugs are located by engine head. You can use a ratchet wrench and sockets to remove them. Make sure to mark the plug wires so the order doesn't get mixed up.
The check engine light comes on when there is a bad sensor, or bad circuit.
Many part stores will run an engine diagnostic code scan for free which will pinpoint exact problem that is setting of the check engine light
The light can only be shut off by the diagnostic scanner!!

could be ,also could have a leak in the exhaust

If you have a small odd shaped key on the keyring there is a socket under the steering wheel (in the plastic housing) which mine fitted. By turning the key left or right in the socket it resets the light. I found that the flashing light indicated that the alarm had been triggered at some time when I had been away from the car and had switched itself off after a time. If you have this key you could try that.

I don't think it's related but have you topped up the oil?