Strange issue - Tahoe dies overnight but battery and alternator are good

[Alexandervj]

My girlfriends 2009 Tahoe has been having this issue for the past 3 days. When we first noticed it we had just taken it to wash and clean out and then driving home the radio kept randomly switching between the radio and the auxiliary input. The auxiliary input hasn't worked in years. And then she drove it to work the next day and when she tried to start it up after work it was completely dead. I had just put in a new battery a year and a half ago so I didn't think it was the battery. She got it jumped and we took it to autozone, they checked the battery, alternator, and starter and they all were good. We attributed it to her accidentally leaving a light on or something but it happened again the next day. She got it jumped again and drove it home and left it overnight, now it won't start again. No lights turn on, doesn't click, even the power doors won't work. I have no idea what's going on. Seems strange this started happening right after the radio had the weird spasm where it randomly went back and forth between the radio and auxiliary input though. Any help would be appreciated

 

[Fless]

It's not really all that strange; there are many threads on here about parasitic draw. Here's one with some good info:
https://www.tahoeyukonforum.com/thr...-temporary-loss-of-power.123548/#post-1518888

When the truck is running and you shut off the engine, pull out the key but leave the radio on. It should stay on for about 10 min. or until you open any door (RAP). If it doesn't shut off when a door is opened, suspect one of the door latches.

Have the battery load tested.
Have the alternator tested.
Check both battery cables, they are known to rot from the inside out, not always visible.
Check and clean the engine and body grounds.
Pull the PCM connectors and check for corrosion or damaged pins and contacts. This might show up as a draw across one of the PCM fuses.
Go through some parasitic draw tests as shown in some of Eric O's YouTubes (in the link above). Be sure to give the modules time to go to sleep.

 

[swathdiver]

My girlfriends 2009 Tahoe has been having this issue for the past 3 days. When we first noticed it we had just taken it to wash and clean out and then driving home the radio kept randomly switching between the radio and the auxiliary input. The auxiliary input hasn't worked in years. And then she drove it to work the next day and when she tried to start it up after work it was completely dead. I had just put in a new battery a year and a half ago so I didn't think it was the battery. She got it jumped and we took it to autozone, they checked the battery, alternator, and starter and they all were good. We attributed it to her accidentally leaving a light on or something but it happened again the next day. She got it jumped again and drove it home and left it overnight, now it won't start again. No lights turn on, doesn't click, even the power doors won't work. I have no idea what's going on. Seems strange this started happening right after the radio had the weird spasm where it randomly went back and forth between the radio and auxiliary input though. Any help would be appreciated

It's still probably the battery. Most parts store employees do not know how to properly load test a battery or look for bad cells. On the other hand, the radio or something else like the BCM could be grounding itself out and draining the battery. A bi-directional scan tool has the ability to look for parasitic draws and can even determine the health of the battery usually.

When a battery starts to go, it creates all kinds of havoc with the vehicle's electrical system, just as you are describing too!

 

[kbuskill]

First of all you need to actually test the battery voltage when the truck is "dead".

The next time it is dead, instead of jump starting it, try grabbing the battery cables and moving them around and see if you regain power.

The cables on these trucks are notorious for corroding internally and causing the exact symptoms you are describing.

 

[Rocket Man]

Truth ^^^^