LBZ GPCM Issues

[buckeyefarmer10]

I cannot get any communication with my GPCM. swapped out both the module and the ecm and still no communication. im thinking its most likely the ground at this point. has anyone dealt with this issue before? looking for some help here with the cold temps setting in here this past week. thanks

 

[TheBac]

Moved to LBZ section.

 

[2004LB7]

Welcome

I'd be probing for power and checking the serial data lines. If I'm not mistaken, the ignition power feeds the ecm ignition power as well as the GPCM. Verify the fuse and power through the ignition to the GPCM is good. Then prob the serial data lines. Should be 60 ohms. Two 120 ohm resistors at each end. Together making 60 ohms if the circuit is complete

 

[buckeyefarmer10]

what fuse is this ran thru?

 

[2004LB7]

I believe it's labeled ignition 0

But if it's blown or bad your engine shouldn't start as it also powers the ECM. But should be the same line supplying the power to the GPCM

 

[JoshH]

Check the power on the large gauge cable that powers the glow plug module. I believe it needs power for the GPCM to communicate.