My first experience with this problem was 2months ago. I noticed that my clock was not keeping time and my door opener would not work, but it was still cranking fine. One evening it would not start no dashboard lights no clicking when you tried to start nothing. I got a jump started right up, the person jumping the Tahoe suggested we turn it off and try starting again, it would not start, we jumped it again but it did not start right up so we waited tried again and it started. I drove home 45 miles. Next morning it started, but clock was wrong time, went to auto zone where I had bought the battery a few months prior. The battery and alternator check out fine. Drove to dealership they checked everything cleaned all connections checked modules could not find anything. I have driven the car for 2 months fine until last Thursday afternoon the Tahoe would not start. Door locks would not work dashboard no lights no clicking when trying to start dead.
Next morning called dealership they could not jump with booster had to jump with another truck. It has been at the dealership since then and they have checked everything and cannot find a problem. Once again they checked battery, alternator, fuses, modules. I asked them to check negative battery cable from battery to head to frame they did not think this was the problem. I also asked them to check ground wire, starter sensor, and MBEC fuse. They said all was fine.
What should we check next? I need my car.

 

How many miles on the vehicle?

Brushes on the alternator could be worn short making intermittent contact.

it would still otherwise check out fine as long as contact with being made when it was being tested.

Anytime mine has had problems like this in the past it was because the battery was bad.

Did you replace the battery because you were having these problems or did you replace it for another reason?

 

About 150,000 miles. I will ask the mechanic to check the alternator brushes. The vehicle has never stopped while driving, only after I have parked it and then try to start. Thank you

 

The battery was bad that is why I replaced it.

 

I suppose it could be the alternator at those miles but mine didn't finally go out until 236,777 miles. Just before that, there were a couple times where the battery was dead the next day and a few times where it was slow to start.

Alternators are expensive and I'm a complete DIYer so I rebuilt my own alternator. The brushes aren't easily accessible and requires a high power soldering iron or small torch. When I got it open, one brush was worn so much that the wire connected to it was keeping it from making contact. The other still had some life to it. The slip ring metal was worn down considerably as well. I replace the bushings, slip ring and bearings. Runs like new and much cheaper than a replacement $180 reman alternator.

 

Even though the battery and alternator test out fine, doesn't mean they are actually good. Since your first battery was having issues and you replaced it and now the second battery is having issues, I'd be suspicious of the alternator. You should monitor your charging system while you are driving to see if voltage is too low at times. This will require a scanner than can do such a thing.

When mine was having charging issues where the battery was dead after a few minutes of turning if off, it always tested fine at the places I took it. I ended up just replacing the battery and all was well.

 

Thank you. I will have him look at your suggestions.