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Who Awoke First?
Posted to Technical Tips Forum on 1/8/2016 17 Replies

Not long ago, I read this post...

This had to do with a draw with multiple modules awakened. What caused the mass awakening - who woke up first? With a G.M. car, you can use the Network Diagnostic tool for assistance. Most draw problems are caused by low speed modules as they don't need a continuous discrete signal to awaken as high speed modules do.

This vehicle is a 2012 Cruze with a complaint of battery going dead if not driven for several days. The battery tested out good and the key off draw was only 13 ma after the modules powered down. I removed the key from the vehicle and waited for the modules to power down, then, reaching in through the window, attached the MDI to the DLC.

Next, initiate the Network Diagnostic Software, select terminal 1 for the LSGMLAN network and enable the message monitor. You can leave the car like this for hours and check from time to time to see if any modules awaken. The screen will stay blank unless some activity occurs. After four hours, I checked the status and saw this....

[2012 Chevrolet Cruze LS, ECM/Inputs/Outputs Scan Data]

Do you see whats occurring? It shows which modules awakened and which were the first to wake up. In this case, the HVAC and the BCM were the first to awaken. The idle time is how much time has passed since they went back to sleep mode. In this case, about 1 hr and 54 minutes.

Which awoke first, the BCM or the HVAC? If the BCM had woken first, all the other modules would have been woken simultaneously by the BCM. Instead, the HVAC woke first, awakening the BCM which awoke the other modules, causing the intermittent draw. Unplugging the HVAC module caused the draw to cease and was the cause of the problem.

How's that for another weapon to find key off draws?

James from Florida

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car Vehicle Data

2012 Chevrolet Cruze LS 1.8L

Engine1.8 L
Trans6-speed Automatic (Electronic)