I recently purchased a 1999 Sierra.The check engine light was on.My code reader does not function when hooked to the sixteen pin connector.Can someone tell me which of these pins are actually used for code reading.This code reader works on other vehicles so I know it's not that.Is there a fuse or circuit breaker that could be blown?Open for suggestions.Thank you

 

The best thing that I found for those trucks is Diablo Motorsports programmer.Its 350.00 but you can watch your engine vitals, o2 voltage and range, timing issues, mass air reading and voltage. its worth every dime to invest in one, not to mention its the only way if you plan any mods to correct the in the ecm. also with that programmer and a laptop you can write your own programs, thats how i tweak mine, and monitor vital signs. hope that helps.