Electrical – Should I remove the termination resistor from the CAN Bus transceiver module

I think this will be safe. My reasoning is this: - the vendor of the cruise control hopefully made sure not to interfere with the OBD-IDs (AFAIK 0x7DF and 0x7E8, both fairly high ids for an 11-bit identifier). - the bluetooth module will (hopefully) only use OBD-ids.

If you don't trust the vendors of both devices, you should not connect them to your vehicle even only one at a time. CAN is a very robust protocol, the worst case scenario would be for the bus flooded with collisions for a short period of time until one of the devices involved would stop sending messages. I'm not sure what exactly would happen in this case, but I'm positive that uncontrollable acceleration will not happen: Manufacturers are aware that a failure of the CAN bus can happen any time (just think of a short between both lines).

This is a very good question. As a general rule, CAN requires a transceiver for every node:

However, under certain circumstances, you can actually get away without any transceivers! Those circumstances are:

• Short bus length (much less than 1 meter)
• Preferably all microcontrollers are on the same PCB, or stack of PCBs.
• The bit rate is low
• The environment isn't too electrically noisy

These aren't hard rules. You might get away with maximum bit rate (1MB/s) if you have a really short bus (10cm).

To achieve this, you need to know a little about what the transceiver does. Like most transceivers, they can output a high or a low to the bus (representing 1 and 0), but the 0 can dominate a 1. I.E. If two transceivers try to speak at the same time, and one is saying 1 and the other is saying 0, then the 0 will win. We can re-create the same situation simply using diodes:

See the Seimens application note AP2921: On-Board Communication via CAN without Transceiver

But here's something even more interesting: The PIC actually has hardware support for transceiverless CAN!

You can configure the CAN TX pin so that is behaves in exactly the same way as the transceiver. This means you can wire up the CAN bus without the diodes. You'll still need the resistor though.