V1 P12 ECU/PCM

[Dominicnicklyn]

Id like to discuss the p12 Pcm and how it functions and its limitations.

From what I understand C1 pin 20 is constant 12v. C1 pin 19 is ignition controlled 12v (from BCM), as well as pin 18.

C1 pin 13 is 12v supplied from the Powertrain relay and ecm/pcm fuse, the ecu must boot partially for this due to it being toggled by an ecu controlled ground.

C1 pin 56 is a ground that allows all of the 5v ref grounds to return to chassis, and C2 73 is a main ecu ground (large bk/wh)

Of course C1 pins 1 and 2 are for the GMLAN

 

[Dominicnicklyn]

My car seems to not have any ecu functions atm, im wondering if I am 100% correct with this and how the c1 13 actually functions?

 

[Gtstorey]

Id like to discuss the p12 Pcm and how it functions and its limitations.

From what I understand C1 pin 20 is constant 12v. C1 pin 19 is ignition controlled 12v (from BCM), as well as pin 18.

C1 pin 13 is 12v supplied from the Powertrain relay and ecm/pcm fuse, the ecu must boot partially for this due to it being toggled by an ecu controlled ground.

C1 pin 56 is a ground that allows all of the 5v ref grounds to return to chassis, and C2 73 is a main ecu ground (large bk/wh)

Of course C1 pins 1 and 2 are for the GMLAN

Have you looked up thee wiring diagram and pinouts from a real source for your donor? That should answer all of your questions.

 

[Rauq]

From what I understand C1 pin 20 is constant 12v.

From the connector pinout, sure.

C1 pin 19 is ignition controlled 12v (from BCM), as well as pin 18.

From the Power Distribution Diagram 2, disagree. C1-19 is fed +12v via the Run/Crank relay (which is maybe what you mean by "from BCM", I didn't follow what pulls down the Run/Crank relay) and then the ECM/TRANS fuse. C1-18 is "Accessory Voltage" from the connector pinout, I didn't find it on a diagram at first glance.

C1 pin 13 is 12v supplied from the Powertrain relay and ecm/pcm fuse, the ecu must boot partially for this due to it being toggled by an ecu controlled ground.

Again I didn't trace down what pulls down the POWERTRAIN relay, but C1-13 is Ign 1 Voltage and C1-38 looks like a PCM toggled ground, from the ENGINE CONTROLS SCHEMATICS.

C1 pin 56 is a ground that allows all of the 5v ref grounds to return to chassis, and C2 73 is a main ecu ground (large bk/wh)

Not super accurate, from the Engine Data Sensors - 5-Volt and Low Reference Bussing, C1-56 is one of like 12 different 5v low ref pins on the PCM. I didn't look for C2-73.

Of course C1 pins 1 and 2 are for the GMLAN

Yup.

I'm confused on what "My car seems to not have any ecu functions" means and how you arrived at C1-13 as the +12v supplied by the POWERTRAIN relay and ECM/TRANS fuse as your culprit.

 

[Dominicnicklyn]

Have you looked up thee wiring diagram and pinouts from a real source for your donor? That should answer all of your questions.

Yes, this is what it is telling me.

 

[Dominicnicklyn]

From the connector pinout, sure.
From the Power Distribution Diagram 2, disagree. C1-19 is fed +12v via the Run/Crank relay (which is maybe what you mean by "from BCM", I didn't follow what pulls down the Run/Crank relay) and then the ECM/TRANS fuse. C1-18 is "Accessory Voltage" from the connector pinout, I didn't find it on a diagram at first glance.
Again I didn't trace down what pulls down the POWERTRAIN relay, but C1-13 is Ign 1 Voltage and C1-38 looks like a PCM toggled ground, from the ENGINE CONTROLS SCHEMATICS.
Not super accurate, from the Engine Data Sensors - 5-Volt and Low Reference Bussing, C1-56 is one of like 12 different 5v low ref pins on the PCM. I didn't look for C2-73.
Yup.

I'm confused on what "My car seems to not have any ecu functions" means and how you arrived at C1-13 as the +12v supplied by the POWERTRAIN relay and ECM/TRANS fuse as your culprit.

C1 19 is from the run/crank relay, but thats after the bcm. The ecu controls the Powertrain relay to alow 12v to be sent to C1 13.

I worded this kinda weird, but essentially im wondering what is needed for the ecu to "turn on".

Im assuming its just 12v on the 19 and 20 pins and the grounds???

My ecu doesn't "turn on" and im wondering what's required for it to function.