[Aussie Mike]

Different generation of ECU for the LS1 but I reckon the philosophy around the high and low speed fan is probably the same.

On the LS1 there was only a high speed output on the ECU. The low speed was done by the BCM.

Hopefully an expert can chime in here and let us know if both outputs on the E38 ECU run off temp or if the low speed runs off an AC trigger.

It'd be nice if they both did as you could use a dual SPAL fan setup from a late model Falcon or similar and have the two fans triggered independently.