SAAB 2007 9-7X w/4.2L engine - car will not start. Keyfob cracked.

"It is saying" - what is "it"? The diagnostic tool is not telling you that you need to replace the PCM, it is saying there is a concern present. Likely there is a relationship issue between the "new key fob" and the PCM. The vehicle must be programmed for a relationship to exist with the new key. I would suggest that you need to seek the guidance of a GM dealership that can work on the anti-theft key programming of this vehicle. Additionally, it could be that your new key is not compatible for some reason. Use this link to find some shops near you that can help with your concern: www.repairpal.com/repair-shops