2005 Lacrosse 3.6L V6. When ign key is turned on the ECM will not wake up until I apply 12v to the starter solenoid terminal . After 12V is applied the ECM wakes up the SES light is on there is comms with scan tool and the ENG will start . If i cycle the ign key off and the ECM powers down , when the ign key is turned back on there is no SES light no comms and no start. the ECM , BCM , TD module , the ign switch , and underhood electrical center have been replaced. also have checked all powers and grds to all modules as well as the comms ckts . what i need to know is "What signals the ECM to wake up when the IGN switch is turned on". Also all parts are GM parts no aftermarket stuff

Why was the ECM, BCM, TD and ignition switch replaced?

The Bcm receives the signal from the ignition switch, then sends signal to the Ecm.

Tech said replaced ECM because no SES light on and no COMMS with scan tool. Said BCM replaced because not sure of IGN 3 voltage (12 volt refernce) was only 11.3 volts compared to Batt volts (12.3) . TD module and IGN switch because could not find anythig else wrong . So now I have it . my confussion is "what is the signal to wake up" is it the IGN 3 (12v refernce) or what. the other thing that has the other Tech unsure of is the IGN 3 voltage. he tells me that when he checked it with a volt meter (11.3v) when he uses his test light he said the light was dim and the voltage drops down to 2-3v. I have double checked the voltage and grounds to the ECM and find NP. So looking at the diagram above if you turn the IGN key on there will be no SES light , go to connector C107 term E and apply 12v to the PU circuit and just make the starter solenoid click the ECM will wake up and eng starts and runs with NO DTC'* . I also double checked all grounds , NP found

This was a GM tech that replaced 3 modules, an ignition switch and UHBC, and it is still doing the same thing? Did you pay for any of this? If you did I would be calling Customer Assistance to get some reimbursement for this....

If this was in my shop, you would have had a loaner until this was fixed.....

Hello there!
We're you able to fix it?
I have the same car and it'* having the exact same issues across the board. Low voltage on ign3 also.
Thanks is advance!

If you checked he hasn't been here in 8 years.

Yeah I seen that but I was just hoping maybe he'* still got the same email address that he used to sign up with and that he'd get a notification from me haha
Wishful thinking I know 😉

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