Service engine light on, how to read codes manually?

[farnorth]

I now have the service engine soon light on at 78,000 miles. Is there a way that I can read the codes myself to know what to replace. I would imagine it is the oxygen sensor. Any thoughts?

[GMCTech]

Unforunately there is no manual flash code retrieval process.

But, if you bring it to AutoZone they will scan it for free. Just don't let them do any work on your truck.

Hope this helps.