MSefi.com read only forum (Jan.15,2018)

I am configuring my MS to switch my radiator fan relay (ground switching mode) using IAC1. I am speculating that because the IAC outputs are rated to switch an idle air valve, that I do not need to use an interposing transistor to handle the relay coil current (about 35 mA). I am also speculating that because the IAC a and b outputs are complimentary (switch between ground and + 12 v), that when the fan switches off IAC1 will go to 12 v which should eliminate the need for a recirculation diode across the relay coil terminals, or would the addition of the recirculation diode be a good idea?

Never does any harm to fit a diode across an inductive load to prevent any spikes damaging the driver. Given they cost pennies.

I did a little checking after I found the part # for the IAC driver chip. The UDN2916LB full bridge motor driver chip used on MS2 already has internal fly-back / recirculation diodes so no external fly-back diode is required.