I will Echo Boosted Diesel here as well: A Blown fuse is not a cause it is always a result! Fuse 36 in the Mustang Provides VPWR (System Voltage in Start or Run see attached diagram) to both the IPC and the PATS transceiver both of which are PATS control modules(IPC contains the PATS memory and program control and the Transceiver, Around the key barrel, reads and transmits the Key signature)! Something in one or the other of these two modules or in wiring, is the problem and is causing the P1260 to set as it is probable the key signatures are not being read or transmitted!Capnscoobing wrote: Tue Sep 23, 2025 9:53 pm For the past few months I was randomly blowing the PATS fuse (36). It had blown 3 times but not in a row. This last go round, it immobilized. I checked the starter (jumped it), tested the engine fuse box, tested all the relays, inspected and tested all the fuses, tested the battery. All came back good and had no signs of damage, with the starter also turning over when jumped. I then went to the interior fuse box (were 36 is located on my car). Again I tested all the fuses and inspected them, tested the relay, inspected the box, and unplugged and inspected all the harnesses. Everything tested good and looked good there. I ran forscan with the recommended vlinker fs cable.
The scan showed p1260, and also dtc U300a-94. From there, I replaced the ignition switch (I had also noticed some play in the ignition and the key not locking into place correctly). I then attempted to restart the vehicle using both keys I had, which prior to the p1260 started the car without issue. With the ignition switch replaced it stopped coding u300a-94. It wasn't reading the keys. I attempted to just reprogram them to the vehicle using Forscan and going through the process it recommended of deleting and then adding them back to the vehicle. I went through the entire process then failed at the reprogram.
From what I've seen online, I cant program 'new' keys while the p1260 is active? Which may be why they failed to program... I haven't had a chance to pick up new batteries yet but will be doing so on Thursday. I have a locksmith coming Friday. He states he can reset the immobilizer and program the keys. If that doesn't work, i plan on ordering a replacement ignition transceiver ring.
When I get some time on Thursday I'll add the forscan info.
A simple DTC check for a missing DTC B1601(unprogrammed Transponder was read) with an unprogramed key used to turn the ignition on would have revealed this as a possibility!
A continuity check with an Ohm meter(Both ends disconnected and the fuse pulled) of the wires shown in the attached PDF should be done before condemning either module to make sure there is no wire shorted to ground or shorted in the harness(no reading between the connections) and 5 ohms or less, end to end on each of those wires!
Hope that was Understandable?