I have wired up the Racecapture (not Pro) using about a 60cm length of CAT6 ethernet cable with the RJ45 connecting to the RaceCapture, and a crimped AMP connector for the front Aux CAN connector on the Haltech as shown in the photo below.
Note that, as the CAN HIGH and CAN LOW uses pins 2 and 3 on the RJ45 connector, they are not part of a twisted pair. I didn't think this would make a big difference given that cross talk isn't an issue (as other wires aren't carrying signals) and it's a short length.


On the Haltech, I have set up the CAN Aux connector and enabled OBDII as follows.


On the RCP, it is set up with a 1MHz baud rate (as per Haltech CAN Protocol document) and a few test channels added in.
Now initially when I plugged this all in, it seemed to work. But after disconnecting the battery to do some other work on the car, and reconnecting, it no longer pulled in any OBDII data, listing "pid read fail" errors.
Thinking it might've been a loose/broken connection on one of the CAN wires (still was receiving power fine), I bought another ethernet cable and recrimped it - this time providing some strain relief by using lots of heatshrink (which is what is shown in the photos above). Again, it seemed to work when I first hooked it up. But after disconnecting and reconnecting the battery, it once again lost all OBDII information.
Don't have a screenshot of the logs, but they are the usual "OBD2: pid read fail" error.
Any ideas on what the issue might be, and what the best way to debug this is?