HP Z6 G4 + W6600 “CPU2 Fan Not Detected” Error

I recently installed a Radeon W6600 for GPU passthrough to a MacOS VM.

I have passthrough fully functional with a single CPU installed, but adding my second CPU to the system causes the UEFI to throw a “CPU2 Fan Not Detected” error and rev all system fans to their maximum.

Taking the W6600 out resolves this error; adding it back in causes it.

Any ideas?

I have configured a Z4 G4 at one point, it shipped with no PCIe cards but on adding one, a fan missing error presented (naturally it shipped without that part).

My interest at this time in trawling the HP docs for a primary source to this rounds down to zero, however what ‘causes’ it is, the nanny bios specifies active cooling variably, according with the PCI card(s) present and thus heat it assumes you’re adding.

From a workstation point of view, a requirement for a consistent behaviour does make a certain logical sense. It fails to safe default.

There may be another fan unit for your chassis it is expecting to find.

901-Chassis, Rear Chassis, Front
Chassis, or PCIe blower Fan not
Detected

do all of these exist.

If you added in a fan splitter for the GPU to run on: say from the chassis fan header.
Make sure one of the splitter sides has four wires and that the chassis fan is connected to it.
Put the GPU fan on the splitter side with only three wires. I ran into this on a couple HP workstations.