Posted to Technical Tips Forum on 1/8/2016
17 Replies
Not long ago, I read this post...
http://members.iatn.net/forums/read/msg.aspx?f=forum2&m=410791&fv=0&ar=3730
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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