2002 Chevy, Astro van all-wheel-drive 4.3 leader replaced the thermostat took off the housing there was one ground wire on the housing cleaned it reinstalled everything and truck will not start the security isn't flashing but I lost the check engine light doesn't come on when you turn the key to the on position and I had three quarters of a tank and that reads empty I also hooked up my scanner and it cannot communicate with the computer onboard computer I checked all fuses inside and under the – all are good even the cigarette lighter I've tried the reset for the security that doesn't work any advice would be greatly appreciated as I am a school bus driver and I really need this car bad thank you

 

will the scan tool power up and then not communicate or not even power up.

if its the latter, goggle diagnostic link connector diagram. from the pic find pin 16. this powers the scan tool. check it for battery voltage.

 

Thank you for replying. Yes when I plug in the scanner there is power to fire it up. The only electrical i touched was a ground wire on the thermostat housing which I cleaned before reinstalling it. It just seems it has to be something in common with the fuel gauge reading empty and the no check engine light at key on.... thanks

 

try a different scan tool.
ideally, use a full function scan tool that can communicate with all the modules not just the pcm. With this, you will be able to know if all modules communication is down or just the pcm.