Appreciate the info. I'll have to figure out which wires go from sender go to the BECM directly.I've just had a double-check and the separate wires from the BECM to the cluster are for tacho/speedo. The serial link takes the information for the fuel and temp gauges - so if the other functions in the cluster are working OK, then the issue isn't the wiring between BECM and cluster.
If the BECM and cluster have been swapped and no change - then your issue has to be in the wiring from the sensor to the BECM.
The temperature read on OBDII comes from the engine ECU only, if you are using a generic scanner. I think you can read a temp on the BECM but would need something like a Nanocom to access that info as generic scanners wouldn't be able to get the data from the BECM. But if the engine ECU is reading a temp the the wire to that is OK. The BECM uses a different temperature sender (in the same sensor housing on a Thor vehicle though) so from the sensor there are 4 wires - 2 will be sensor grounds, and then one goes to the engine ECU and the other to the BECM.
I would be guessing that there is an issue in the wiring from the sensor to the BECM if everything else is checking out. Reading a temp on OBD from the engine ECU just proves that the sensor and wiring for that is working OK, but could still be an issue in the other wire from the other part of the sensor to the BECM.