I have got a 2003 F150 5.4 that cranks but won’t start, and the THEFT light is flashing (code 12).
Here’s the backstory: Originally, it was a No Start/No Crank issue, but the THEFT light wasn’t on. Thanks to threads on this board, I traced the problem to the key cylinder not properly engaging the actuator rods. The ignition switch is fine (I was able to start it by unbolting the ignition switch from the column and manually moving the mechanism). However, during troubleshooting, I accidentally unplugged the wiring harness from the ignition switch while the power was still on (I thought it was off). After this, the THEFT light started flashing code 12.
After fixing the ignition issue, I turned my attention to the THEFT light. I was hoping it might just be a fuse issue, so I traced the power from Fuse 30 in the cabin fuse box to the PCM diode, then to the PCM relay, and from there to fuses 23 and 18 in the under-hood fuse box. So it looks like power is reaching the PCM. I also pulled the wiring harness from the PCM and confirmed there’s 12v on pin 55, so the PCM seems to be getting power. This video was really helpful, so I’m sharing it in case others need it:
My question is, what should I do next? How can I determine if I’ve fried the PCM or if it’s just stuck in THEFT mode? Could the transceiver be dead?
One other detail: the odometer display is blank (not showing dashes). I’m fairly certain it wasn’t blank before, but I’m not 100% sure. This truck is on an island, and getting it to a dealer would require a barge, so either it gets fixed here, or it may be out of commission for good.
Any help would be appreciated!