I have a 2009 F150 Lariat 5.4. I recently got a new PCM because Ford told me that they were unable to see transmission data as said the PCM was failing. Come to find out the transmission was the problem. Got a new transmission anyway. My question is I am have some issues with the new PCM and need to send it back for repair. I still have my original PCM and it does work so I want to know if I can put the old PCM back in my truck while the new one is getting fixed? Thanks.

 

If BOTH PCMs worked, that would mean they were programmed for your vehicle.If you installed a PCM that was not programmed to your vehicle , neither PCM will work anymore because the system is confused and will require the PCM to be reprogrammed to "as built " specs. At this point only a certified locksmith with clearance or a dealership or certified shop with clearance can now do the reprogramming