Unfortunately, there is not a reset process for the FCM as it is just a printed circuit board type module. It is unlikely that the replacement FCM had the exact same failure as the original so I am thinking you have an issue with the IPC circuit board. Basically the way this works is the FCM sends the voltage to the relay that is on the IPC so if you have two FCMs that are not getting power to the relay, then I would think the issue is in the IPC.
Unfortunately the only way to test this theory is to use a scan tool and go into the FCM and command the relay on. If it comes on using the scan tool then the FCM is the issue. If it still does not come on then there is an open between the FCM and relay terminal.
This voltage is supplied as soon as the key is in the run position so I am thinking another way we can try and test this is to see if there is an open between the FCM connector and terminal 86 of the relay. So remove the FCM and the relay and then use your meter on ohms and touch one lead to pin 37 of the IPC side of the connection with the FCM and then the other lead to terminal 86 of where the relay goes. There should be less than 1 ohm of resistance. I am hoping you will see this is high or even an open circuit which will prove the IPC is the issue.
At which point, you can either replace it or just run a wire that is hot in start/run so that you have power there in those key position. You don't need the FCM supplying this as the PCM is responsible for grounding it to control it so as long as you have voltage there then that is all you need.
Does that make sense?
Images (Click to enlarge)
Saturday, January 16th, 2021 AT 6:30 PM