I have an'06 Silverado 2500 diesel that starts some times but not others. A boost will work if left connected for 5 minutes or so. It seems to happen more so in the cold weather (8 F right now). Had the batteries tested after a boost and a 1/2 drive to the service center, and they read good.

My real wonder is why it happens after a clean start and then a couple of short stops doing errands, and then all of a sudden, no start? A mechanic friend suggested a short, so I disconnected my brake controller which was the only after market addition to the truck, electrically. Seemed to be fine until this recent cold snap.

Alternator?? Any help is greatly appreciated

. Remove and fully charge the batteries. Add distilled water, if necessary.

. Clean battery terminals, cable connections, and inspect ground.

. These links should help:

https://www.askmehelpdesk.com/cars-t...ml#post1973613

https://www.askmehelpdesk.com/cars-t...ml#post1415281

. Use full-synthetic HDDO.