I am working on a 2006 impala with 119,000 miles and it has a huge battery drain on it. The customer say he can leave the key in the ignition and it doesn't seem to drain while it is parked. It has codes U0073 and U0140 in it and I have also noticed that the ignition won't turn back to accessory, also have pulled all the fuses and relays out one at a time and didn't affect the draw, while I had my multimeter on between the negative side of the battery while cable is disconnected. I even disconnected the BCM, the radio, and the cluster since they are known problems but didn't make a difference on the draw. Alternator is charging good and it doesn't have a draw on battery, anyone have any ideas, its getting really irritating.