I have a 2019 2wd surburban and occasionally it won't start.

The battery is good. It has been checked by me and three professional mechanics.
The alternator is also good
Starter is good
Battery cables are clean and tight.
I've gotten an alert on the dash that states that the "Trailer brake system needs to be serviced" The trailer brake system has never been used.
Shortly after getting this alert the suburban won't start. It will only click a few times. If I try to use a battery booster it won't start but, if I jump it with my other truck it will fire right up.
It has ran for two weeks with no problems. Yesterday the alert come on. I drove the sub for 20 minutes today. Shut it off, went into my house and came back out 5 minutes later and it wouldn't start.

Does anyone know what Gremlins could cause this and is there a fix for it.
I haven't taken it to the dealer yet.

Thank you any help is appreciated .

 

Welcome to the forum. Sorry I missed this but I will move it to the Suburban section now.

 

sounds like a bad or discharged battery....or loose battery connections.
what is the open circuit voltage of the battery?
post the fault codes in the ebcm. if its low voltage codes...its from...you guessed it...the battery.
no one load test the battery properly anymore. these days its all conductance testers which don't put a real load on the battery.
cold weather like this can reduce a full charged battery capacity to under 40%

 

I'll second bad battery. I've had 3 batteries in the last 15 yrs. fail from having bad internal connections inside the battery. Giving the battery a whack or even slamming the hood on one of them made it connect and crank over fine. Jump box's will not start a battery in that condition only a full jump from another vehicle.
Other tip off is a weird failure message like the trailer message. Low voltage will make modules say and do wacky things.

 

Thank you "tech2" and "repairman 54" for your time and input.
It was the battery