Sorry to hear about your dad. I've had same bad expirences with GM.

I wanted them to read a code for me and they said they couldn't because it made a wierd sucking noise and that something was broke. I had to go to the service manager and said I'm here to read a code and I ahve the 40 bucks. Will you read the code. The server tech said again that he should not cause something was definatly broke on my sunfire.

I finally had to show the tech I had a small turbo (snicker T3/T4 Stage 3) bolted on and I had a slight miss and a code.

Long story short they tend to do stupid things when it comes to do much of anything is it appears it might involve work and it's related to warranties. I know GM service centers run from warranty work.

P.S.
it was a bent valvue I replaced before noon...LoL