Airbag/brake witnesses and injection system

Hello everyone
I have recently bought a C2 and everything goes on 4 wheels, hehe ... jokes apart. A few weeks ago, witnesses of the airbag/brakes and injection system are lit, but these go out to the latter, but two days ago I has been fixed by the light of the injection or antipolution site, that I do not know what it means, I feel my ignorance. The truth is that the car is going very well, without losing strength, or speed.
I ask you to help this, I have gone to the workshop and they have told me that it is quite difficult to find the failure, that it must be some clema that is making some bad contact, what they want to tell me (the workshop is where I have bought it).

Thanks in advance to all.