Her_Liberty wrote:
Does anyone know what contsole discovered was the cause of his battery drain?
I spent several days at the dealer and they were never able to solve the issue. Part of their problem was disconnecting the battery as part of their test. This caused all kinds of resetting and recycling and even after they let the car sit overnight, they wouldn't see the problem. The electrical guy they had on it gave me an idea. He said a previous power-draw gremlin he tracked down was related to the slightest amount of rust on a brake light connection. The corrosion was causing noise and retries on the vehicle's communication network (CANbus). When there is noise or an unexpected condition, the computer never goes to sleep and continues to draw power.
I chewed on that for a while and didn't come up with anything. One cold day driving to work I turned on the vent and expected cold air but it was only cool. The temp setting was fully CCW so I knew there was a problem. The motor/positioner (on circuit M13 - see first post) that moves the mixing damper is near the driver's right foot. I removed it and made it move back and forth a couple dozen times and I used a some pliers and moved the damper back and forth a number of times. It may have been sticking a little, not sure because it's harder to move than expected. The damper only has about 90 degrees of movement while the motor has 180 degrees of movement. When the battery is removed and reconnected, the computer orders the motor to perform a crude calibration routine by moving from end to end. There is no position feedback so it probably looks at stall current for the end points and uses time-on as a estimate of position.
I believe what was happening is the damper motor was unable to position the damper as commanded and the computer never went to sleep because it saw an unexpected condition. I never would have been able to trouble shoot this without a DC clamp-on ammeter. The repair technician at the dealer even bought one just like mine after he saw it and realized the value. After re-attaching the motor, the problem never returned.
Postscript: Every time you touch something, even the door light switch, it wakes up the computer and takes between 8 and 15 minutes to go completely back to sleep. It's maddening to troubleshoot. The faint glowing of the VFD dash display I saw in post 10 also disappeared once the sticking damper was addressed.
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