4 ms·

This is wrong. The Cherokee hack existed because both CAN buses in question travel to the infotainment system. The vulnerability came into being by finding a pa

by wwy43 6y ago

This is wrong. The Cherokee hack existed because both CAN buses in question travel to the infotainment system. The vulnerability came into being by finding a path between them. It became remotely exploitable when they found a way to do the same thing over the onboard cellular modem. So no, your definitive crude architecture defect and reference to the 1990s is a misunderstanding of the actual problem. This is a common FCA design. CAN HI and CAN LO often go to the same device on different pins. My Jeep has an instrumentation bus as well and all three arrive in one box in multiple places within the vehicle. Friend with a Rubicon Wrangler discovered both engine buses connect to the electric motor to disconnect the sway bar. He discovered this when water got in it, shorted it out, caught the electric motor on fire while he was watching, and subsequently totaled the ECU and TIPM by transmitting electrical noise on both CAN ECU buses. You’ve assumed one bus goes to one thing to reach your conclusion. That is faulty logic, which is no shortage of ironic given the parts of your comment I’m mostly ignoring in this reply.

redfern314 6y ago
Something doesn't parse for me in your second paragraph - CAN HI and CAN LO are 2 parts of the same bus (each bus has 2 wires per the differential spec) and so of course they go to the same device on different pins. Am I missing something about the Jeep architecture?
- wwy43 6y ago
  They’re two separate buses, high rate and low rate, for different purposes throughout the engine and components. Not the literal high and low pins of each bus. High rate, low rate. Think cylinder timing communication speed versus, say, fuel usage. CAN operates at a fixed speed, and I understand high and low rate buses to be a common design (they’re two CAN standards, high is something like a megabit). My code reader has fetched “CAN HI” before and the code was contextually referring to the high-rate bus, not the physical wire. I’m not a deep Jeep tech, just dangerous electrically and with a spanner, so I may be wrong in how I’m spelling those and I’m following the lead of a trouble code. If you’re nice to a service dealer with a laptop you can get a quite lovely wiring diagram that explains it better.

by wwy43 6y ago

redfern314 6y ago

Something doesn't parse for me in your second paragraph - CAN HI and CAN LO are 2 parts of the same bus (each bus has 2 wires per the differential spec) and so of course they go to the same device on different pins. Am I missing something about the Jeep architecture?

wwy43 6y ago
They’re two separate buses, high rate and low rate, for different purposes throughout the engine and components. Not the literal high and low pins of each bus. High rate, low rate. Think cylinder timing communication speed versus, say, fuel usage. CAN operates at a fixed speed, and I understand high and low rate buses to be a common design (they’re two CAN standards, high is something like a megabit). My code reader has fetched “CAN HI” before and the code was contextually referring to the high-rate bus, not the physical wire. I’m not a deep Jeep tech, just dangerous electrically and with a spanner, so I may be wrong in how I’m spelling those and I’m following the lead of a trouble code. If you’re nice to a service dealer with a laptop you can get a quite lovely wiring diagram that explains it better.