my 2005 f-150 has a check engine light but no codes

My first suspect would be the PCM (computer).The computer will tell on everything else but not on itself! A very good mechanic once told me that once and I've found it to be true. One example was when I was chasing down a security system problem with my 94 Fleetwood. The Passkey Fault light would come on and sometimes the engine would randomly shut down. After exactly 3 minutes the light would go off and the engine would start and run normally again, until the next time. I didn't have any trouble codes from the computer though, so I replaced the computer. That was 4 years ago and, knock on wood, the car's been fine ever since! Hope that helps! Jim