2006 Cobalt SS 2.4L LE5, E67 ECM, T42 TCM.

Does anyone know what the accessory power wire (circuit #4) that goes from BCM "logic" in this diagram to both the ECM and TCM does / is for?



I've got my own theories but wondering if anyone knows for certain?

 

maybe it is to prevent hotwiring of the ignition?

 

im not 100% sure, however i have some thoughts. i know on these cars the ecm will stay live for some time after the key is turned off. my thoughts are this would be to allow the fans to turn on in the event that after shutting the engine down the temp climbed up high enough to trigger the fans (this happens, many cars do this). its also a nice feature for the guy doing diagnostics, when you shut the key off it doesnt disconnect your scanner from the ecm.

my thoughts are, hook it in with the ignition circuit. ive worked with the e38/e67 ecm in ls swaps, i cant say i remember running across an accessory power input, but my instinct tells me hook it to the ignition circuit, so im sure thats what ive done in the past.

 

It's called "Retained Accessory Power," (RAP) and is one of my theories as well. Also Remote Start. And my instinct is to connect to ignition as well. I'd feel better about it if someone knew for sure though.

 

I've all but confirmed that wire is the RAP wire and can be removed. I found a fiend who is using the same ECM on an LS3 installation in a rig, has his engine running, and does not have anything going to that pin.