The light is ridiculous. It should read the code in models that have a text display, instead of needing to go to Autozone and rent an OBD code reader. It's bullshit. Tell me the error up front so I can Google it.
The problem is that the OBD codes aren't always specific. Sometimes they're specific enough to diagnose the problem, sometimes they're not, which is why you still need someone with auto expertise to correctly identify the problem. Most shops will warranty against unneeded repairs as a result of reading the code by virtue of buying their $99 "Check Engine Light Service" (whereas Autozone's reader is free to borrow). I've been in the situation where a shop made a check engine light repair that didn't fix the problem, so they made another $500 repair to actually remedy the problem.
The most unspecific OBD code, IMO, is any EVAP code. Seriously could be 100 things, from as simple as a gas cap not being screwed on, to a tiny leak in a gas line, to a bad 02 sensor, to a dead spark plug, leak or rot in the fuel line, bad fuel pump, dirty fuel filter.... ect ect ect....
