I recently had some airmatic hic-ups, and a rough idle, So I figured I'd take it to autozone for a free scan. Long story short, Two of their code readers found 0 codes, even when we purposefully pulled fuses and unplugged a tail light... They said to take it to MB, and that got me thinking, if the obd-II system itself is broken, how do you diagnose it? And why is my car throwing zero codes, even when its appearent somethings wrong? The IC even told me when I unplugged various things....

 

You can't check airmatic faults with a OBD2 reader. If your car has a rough idle and no CEL i would check the motor and transmission mounts first. Even if you unplug taillights lol it's not going to throw a CEL but rather it will show up in your display cluster as a malfunction. You have to remember the CEL is mostly emission system related and O2 faults.

 

Actually, in one way or another, it's 100% emissions related. benz_addict is correct....a DAS will be required for proper diagnosis.

 

ahh shoot, another trip to the stealer to get raped with fees and "oh we found this and fixed it" claims..