GMC Sierra Cranks momentarily then wont crank again until after a min

scan for codes even if the light ain't on

I forgot to mention about codes. I have tested and have gotten u0100, p0700, u0073. Though each time I test the codes change from either no codes to 1,2 or 3 of the above. I haven’t checked the fuel rail yet as don’t have a pressure tester. As for security I’ve tried my spare key and get the same result and don’t get any security errors. The battery is good and cranks great when it cranks. When it won’t crank it’s as if the ecm has told the starter not to crank any more For some reason but after 30secs or so this resets and I can crank fully again. Also I added a new ground from the engine to the body but with no change. Any other ideas? I really appreciate them!

I have another couple of points that I wasnt sure were relevant. On the dash I am getting errors of : service traction control, service stabilitrak, reduced engine power, Service theft deterrant system,

Hi beatupchevy, Finally figured out what the problem was. The problem was my ECM. It seems that when I went to crank the vehicle the ECM would just die so there was no communication from it to keep everything else doing what it was meant to do. I picked up a better OBD2 which told me when the ECM was live and then when it died. This really helped make the leap to the ECM. I then picked one up from my local car wrecker for 35.00, fitted it, did the key re-learn and low and behold it started! As this replacement ECM was for a different engine than mine, my engine ran pretty rough so I took it into my local GM Dealer where they programmed my truck's info onto this ECM, then they did a crankshaft learn and now my truck is running sweet! Cheers! David