Hi everyone. My FFBH doesn't work. This isn't great, but as a result, my aircon also doesn't work.

I have codes B129A-88 (LIN Bus "D" - Bus off) and B12B9-87 (Auxiliary Heater Control Module - Missing message) from the HVAC module. The workshop manual says that if you have this code, another symptom will be that the air conditioning doesn't work. That's the case for me.

Upon checking the voltages to the FFBH plug, I found that there was some voltage at pin 5 - The LIN Bus connection. There was no voltage at pin 1 - the 12 volt power supply. So I checked the 20A FBH fuse in the lower trunk compartment fuse box (what a pain to get to!), and the fuse had blown. So I replaced it. I could then see data from the FFBH in the live data, so it must be alive. The first thing I tried was to run the timed climate. The fuse blew quickly.

So my initial thinking was that there is some short circuit in the FFBH when it tries to run. When I checked the voltages again, there was 12 volts at pin 4 - the signal from the remote heat receiver. I don't know why there's 12 volts there, I thought that should only happen when remote start is activated. So I decided to eliminate it from my troubleshooting by removing the plug from the remote start receiver. After replacing the fuse, there was now 12 volts at pin 1, some volts on the LIN bus, and no power on any other pin. The ground pin had continuity to ground.

I left it for some time with the ignition off, to see if the fuse remained intact. It did.

I turned the ignition on for a few minutes while I reset DTCs, and the fuse remained intact.

I started the engine, to see if the aircon would work. It did not, but it seems that the FFBH fuse had blown again immediately.

So, in my mind, there's some electrical fault in the FFBH. I can't think what else it could be.

Then I'm undecided whether to try to get hold of a used FFBH and try a straight swap (no guarantee that the used FFBH is good), or take the FFBH apart and see if I can spot anything obviously wrong.

I'd appreciate the thoughts of those more experienced than me!