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The power meter I've had attached to the block heater indicates that it ran exactly 21min 28sec over the past 24 hours. We've been below zero for most of that time and it was -18 at 6a.m. today. The thermostat in mine is pretty close to the engine (not on the exposed male part of the cord), and must turn the unit off after it senses something nearby getting above zero. That heater is a fraud and GM deserves criticism for sacrificing the engine to please the computer. I don't buy the EPA stuff--- nobody else does it. My guess is that it would have cost them a fortune to fix the computer software, so they opted to just jury-rig the heater cord to make it useless. Doesn't say much for Yankee ingenuity. Then again, I guess they'll sell more engines.

Thanks for the info. I checked all the connections and now my ammeter says it's working. Good, as it's -10. Looks like when the ambient air gets to zero it will shut off. I guess if you use that block heater stock, you'd better have a garage. That plug is coming off.

It's -14 degrees F here right now and I got up early to see if the digital power meter I placed on the heater cord would show it's working. It's not, and the KW/hr meter shows it hasn't worked all night. The heater P/N that the dealer put in is 12586687 ($37.25) and the cord is P/N 15801284. The end of this cord doesn't have a "tumor" like the pictures posted earlier, but it costs $129.27 so it must have some type of control in it. These aren't the part numbers mentioned earlier in the discussion so maybe these parts are wrong, or it's faulty or it's not supposed to kick in till -50! Anyone know? It's hard to believe GM would make a block heater like this. Also, the owner's manual does state that the block heater will work below 0 degrees F, and you shouldn't need one above 32F but doesn't address what to do in between 0 and 32F. It would be considered negligent to start an airplane engine at +5F without preheating, synthetic oil or not.

I just spent about $450 to have my local GM dealer install a "genuine GM part" K05 block heater in my 6.0L Sierra. It didn't come with one new. Checked it this morning when it was +2F and couldn't tell if it was working. Thanks for all your posts---now I know it probably wasn't. Nice heater. Anyway, I think the dealers up here do know about all the idiosyncracies with them as my guy warned me not to buy a cheap aftermarket one or the computer would get upset. So I have instead an expensive block ornament. Do all the manufacturers do this or just GM? Seems nuts.