'01 2500hd can't read codes

01' crew cab with an 8.1 in it. has a "service engine soon" light on but everytime a code reader is connected it says cannot connect or cannot read ecm. i have visually and manually checked wiring to make sure connectors were intact. any ideas ? common problem?

01' crew cab with an 8.1 in it. has a "service engine soon" light on but everytime a code reader is connected it says cannot connect or cannot read ecm. i have visually and manually checked wiring to make sure connectors were intact. any ideas ? common problem?

this is most always a blown fuse ...

thanks, i check everything again

Check the cigar fuse. I know it sounds stupid, buts thats where the power on my 2000 comes from. I had the same probem some time ago.