2001 Denali Service Engine Soon Light But No Codes

[gostlrs]

My SES Light will come on & stay on for a while then magically go away for a long time. The last 2 times this has happened I attempted to pull the codes but it acts like the tester is not connected. It will not talk to the computer. Did this at 2 different stores as well. The ABS & Parking Brake lights will come on and off at will as well.

Anyone got some ideas? I figure its a bad ground somewhere since it is intermittent. I am sure this has happened before.

 

[gostlrs]

I am getting voltage on the ODB plug on pin 16 using pin 5 as ground. I found the cig fuse blown & replaced it. Disc battery & rest the ECU but light came right back