I went camping for a week in the CA Sierra mountains a couple of weeks ago. The temps were 20 def F in the morning. The SES came on and a P540 code has been set. Looks like the cool temps (at least by SoCal standards) kept the IAH on too long and something gave way. So we have similar problems.

When viewing the engine from the drivers side fender, the IAH relay is located behind and slightly to the left the two 50+ pin large electrical connectors that the Edge Juice would hook in to. It is above the drivers valve cover, about mid engine.