99ML320 Check Engine Light

After getting an oil change the check engine light came on. The mechanic fixed it and then two days later it came on again. I also recently clean my K&N air filter, does this have to do with the check engine light coming on? I also did the ESS buttoning combination and the light is still on but the meter reads 10000. Can anyone give me some pointers, i dont want to bring it to Mercedes and have them charge my more $$$, I want to fix it my self?

Thanks
Mig888
99ML320