HI GUYS.... 08 F550 NO CRANK/NO START PROBLEM. DASH IS DEAD AND HAS THESE CODES P1260...U0155....U0121....U0073. WAS RUNNING FINE THEN JUST GOT THIS PROBLEM... CHECKED FOR BROKEN WIRES AND FUSES. COULD IT BE THE 'SMART JUNCTION BOX' ??? NEED HELP!!!! !

 

I am pretty sure the P1260 is your antitheft...are you using your factory key?

 

You are correct.
With the other codes though, I wonder if P1260 is thrown because a control module has failed?

I don't have a fix for you but:

P1260 Theft Detected, Vehicle Immobilized
U0155 Lost Communication With Instrument Panel Cluster (IPC) Control Module
U0121 Lost Communication With Anti-Lock Brake System (ABS) Control Module
U0073 Control Module Communication Bus "A" Off

 

I would think the u codes are just related to the real issue. Either a bad key or you are going to have to get towed and reflashed and reprogram the keys.

 

I FOUND THE PROBLEM!!!!!! THE 'SMART JUNCTION BOX' HAD A POOR CONNECTION. I UNPLUGGED IT CHECKED CONNECTIONS AND PLUGGED IT BACK. GOT DASH AGAIN AND IT STARTED. I'M MOBILE AGAIN.

 

Congrats and glad you reported back for others to see.

 

Good to hear...where is said "box"????

 

I don't think the key has anything to do with it. The key reader communicates with the instrument cluster directly.

All those U codes indicate something is messing up the CAN bus. It could be a damaged wire somewhere (mouse season?) or it could be one of the devices on the CAN bus that has gone bad. Since it's a shared bus, any device on it could potentially mess up the bus.

U0073 - Control Module Communication Bus A Off
Description: This DTC is set when the controller area network (CAN) between the powertrain control module (PCM) and data link connector (DLC) is open.
Possible Causes: Communication error

Diagnostic Aids: Network DTC concerns occur during module-to-module communication. For additional description and operation of the vehicle communication network, refer to the Workshop Manual Section 418-00, Module Communications Network.
Application Key On Engine Off Key On Engine Running Continuous Memory
All Refer to the Workshop Manual Section 418-00, Module Communications Network to diagnose the communication network.

U0121 - Lost Communication With The Anti-lock Brake System (ABS) Control Module
Description: The powertrain control module (PCM) continuously monitors the controller area network (CAN) for messages from the ABS control module. This DTC sets when the PCM does not receive the ABS message within the defined amount of time.
Possible Causes: Communication error

Diagnostic Aids: Network DTC concerns occur during module-to-module communication. For additional description and operation of the vehicle communication network, refer to the Workshop Manual Section 418-00, Module Communications Network.
Application Key On Engine Off Key On Engine Running Continuous Memory
All Refer to the Workshop Manual Section 418-00, Module Communications Network to diagnose the communication network.

U0155 - Lost Communication With Instrument Panel Cluster (IC) Control Module
Description: The powertrain control module (PCM) continuously monitors the controller area network (CAN) for messages from the instrument cluster control module. This DTC sets when the PCM does not receive the instrument cluster control module message within the defined amount of time.
Possible Causes: Communication error

Diagnostic Aids: Network DTC concerns occur during module-to-module communication. For additional description and operation of the vehicle communication network, refer to the Workshop Manual Section 418-00, Module Communications Network.
Application Key On Engine Off Key On Engine Running Continuous Memory
All Refer to the Workshop Manual Section 418-00, Module Communications Network to diagnose the communication network.


http://wpnet.us/Comm_Network.pdf

http://wpnet.us/Comm_Network2.pdf

EDIT: I see you found the issue, very fortunate. If you read those comm network docs you'll get an idea of how the system works and how complex it is. Look at all the messages carried between modules on the CAN bus and imagine if it was the old days where each was an individual wire between devices.

 

The SJB is in the passenger side footwell on the right side behind the carpet and under a plastic cover. Good to familiar with the location since there are many fuses there in addition to the BJB under the hood by the brake MC.

 

good to know!