So this is going to be a long post, but stick with me here. One of my projects is to use Ford's MyFord Touch SYNC system in a stand-alone application (i.e. - my 2003 F-250). This system, in it's most minimalist form requires four modules (nodes) to operate.
They are;
Accessory Protocol Interface Module (APIM)
Audio Control Module (ACM)
Digital Signal Processor (DSP)
Front Control Interface Module (FCIM)
These modules operate over three different networks;
HS-CAN @500kbps
MS-CAN @128Kbps
I-CAN @500kbps
So the CBT is perfect to run this operation. All four of these modules receive a constant 12 volts and power on from "wake up" packets sent over CAN. My objective is to copy these packets from a vehicle with the same system (in this case a 2012 Ford Focus). Then re-write the CBT firmware to send these packets based on inputs from the CBT analog inputs.

Here's the problem, I made a OBD-II harness to connect the CBT to the three networks in the vehicle. However, as soon as I connect the CBT to the OBD-II port, the vehicle networks all crash. All nodes appear to crash. Basically, the engine goes into whats know as "Limp Home Mode" or "Fail Safe". Basically, it is a limited operating strategy for fault conditions. Also pretty much every light on the dash comes on, every warning message, and the entire vehicle begins to shut down, one module after another. Usually network screw ups like this can be corrected by simply cycling the key, however sometimes even the ignition switch become unresponsive until the battery is disconnected.

I'm not sure where this problem originates. I tossed around the idea of clock synchronization, as well as, possibly the nodes recognizing the CBT as something that is not supposed to be on the network. Honestly, I'm at a loss for explanation. I did connect the CBT to another vehicle (07 F-150 with only HS-CAN) and and monitored packets with no problem. But, I tried it with two different Focus(s), and both times had the same problem. Has anyone else had an issue like this?

Have you tried setting the CAN Bus network speeds on the CBT first before connecting it to the car? I had this problem with the infotainment CAN in my car, only when I set it to 83kbps manually did I avoid having the CAN network go crazy.


Yep! Your network can haver errors if you connect it at the wrong speed. Depends on your vehicle.

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