My 2008 chev 4x4 has the "auto" 4 wd feature on it and thats what I leave it in except for actual 4wd use. I'm wondering if people have seen fuel mileage increases using the "2hi" setting?
The auto 4wd feature takes advantage of technology that is already on the vehicle to give you instant 4wd, namely the wheel speed sensors used by the vehicle's anti-lock brake system.
When you select auto 4wd, you're engaging the vehicle's front hubs, but not engaging the transfer case that actually sends power to the front wheels. If the vehicle computer system detects rear wheel slip, the pcm or power-train control module will send a signal to activate the transfer case sending power to all four wheels.
Use auto 4wd in situations where you might experience intermittent loss of traction, such as blowing snow, patchy ice or even heavy rain.
As for the downsides of running in auto 4wd, well you'll have both your front half shafts turning all the time. It's up to you if that's a concern. For me I'd use the auto 4wd feature if I suspect I might encounter a low traction situation as I've already discussed. If you're on really slippery surfaces such as snow covered roads, my preference would be to engage 4wd high for continuous power deliver to all four wheels - actually power to two wheels unless you have locking front and rear differentials but that's another topic.
Hope this helps.
