I have a Duramax 2008 2500HD why will it not start or turn over when shut off for short time after warmed up. Have new batterys and been to a couple of different shops. It seems to never fail when taken to shops so makes it hard for them to trouble shoot. I can hear relays clicking when I try to start, but will not turn over. Cold weather I wait for glow plugs but that season is now about over. I'm needing help.
ok, you need to check the basics for a no start, no crank. First thing is: do you have a test light? next time it won't turn over you will have to see if you have battery voltage to the starter solenoid from the ignition switch. It should be full battery voltage (or very close to it). then check the big battery cable that goes to the starter. You want to check them when the key is in the start position and the starter won't turn the engine over. If you have good battery voltage at both terminals I would suspect a bad starter. Try Tapping on the starter with a hammer or wrench while it's in the start position and see if it wants to turn over then. (Again, bad starter if it starts to turn over)
If you don't have good battery voltage at the bug starter cable or the starter solenoid wire check for bad connections between your power supplies and their respective terminals.
check the starter relay in the underhood fuse panel. Sometimes the relay could have burned contacts that don't always connect properly.