Just recently purchased a 2008 H2 SUT. Several times over the past 3 days it has done this weird thing where the locks cycle quickly. (Lock then unlock) And then the transmission seems to drop into an extremely low gear. The engine revs to 5,000+ rpm and the Hummer slows quickly. And then it suddenly shifts back normal gear and everything is back to normal. When this happens it’s very quick. The whole process takes maybe 5 seconds or so. But it’s very frightening because it comes completely from nowhere.

The most recent incident happened at night at night and I noticed then that all the interior light seem to turn off and then back on again. So it’s almost as if the Hummer thinks it’s been turned off and placed into park. Only to realize it hasn’t and it restarts. However, the engine never dies during this process.

I’m both confused and concerned. Especially if this were to happen at higher highway speeds. I’ve never experienced anything similar with any other vehicle. Hoping someone else has had a similar experience and has some idea as to a cause.

 

How new or good is the battery? There should be a date stamp on it - quirky electrical behavior can surface if you've got a low battery condition. I had to replace mine during the first month (also an '08) due to similar issues w/ door locks acting up. Good luck!

 

A bad battery will do things that I never thought was possible. I think autozone can test it for free. If that doesn’t help you might want to consider an Exorcism!

 

Had the same with my 2008 H2. It took several weeks, multiple mechanics, reps from GM, etc to figure out that the Body Control Module and ECM modules both had to be changed. No clue why they were the issue, but I spent over $3k between all visits to get it figured out. And it was in the shop for weeks. Haven’t had the issue repeat in 3 years now and roughly 30k mi later. There was a GM service bulletin or two related to this issue that one of my mechanics found. Good luck.

 

+1 on a battery upgrade...