Teensy CAN project

Hi guys, i'm trying to build a teensy project that listens to CAN messages from my cars ECU. My ECU is a standalone ecu since the car is supercharged, and with that the ECU has an AUX plug that features can/hi lo access. I've spoken to the ECU manufacter and they said I need to have a 120ohm resistor going across the CAN HI + LO. I've done that, but i'm still receiving no messages what so ever, the BAUD rate is definitely correct as that's something I can set in the ECU software, i've tried 250kbs, 500kbs and 1mb. I've attatched a crude diagram to show how i've got it all setup. Unfortunately I am NEVER seeing any CAN messages from my ECU. I'm wondering if it's a wiring / setup issue. Would love some feedback as this is my first attempt at anything like this. I'm using FlexCAN, and when I use the loopback mode I do see messages, so that makes me think the setup is correct, but I may be wrong. I also wasn't sure if the ECU needed to be added a common ground, so if someone could confirm that it would be great! Thanks! Edit: List of boards used https://thepihut.com/products/can-board-sn65hvd230 https://thepihut.com/products/pjrc-teensy-4-0-usb-development-board