2001 V70 T5... My radiator fan stopped working, and I assumed the fan itself was bad and ordered a new one from RockAuto. Put it in, no difference. Finally got my Dice/Vida machine going (an epic tale itself) and tried commanding the ECM to turn on the new fan. Nope... nada.

I checked, and a basic DC voltage reading on the control wire showed that it was changing (from about 1.5V when commanded on 100%, to about 10V when commanded off). Just for grins, I put the OLD fan back in and guess what... it DOES come on when commanded via Dice/Vida. High, Medium and Low all work as commanded. The new fan was just me adding another problem, it turns out. The old one will be going back in.

BUT the fan won't come on when the A/C is turned on, or when the coolant gets to a proper "hot" level (I let it get to 95C just to be sure).

Does anyone out there have an idea what might be causing this? I suppose it could be a bad ECM, but it does work "manually" using the Dice/Vida device.

 

Figured out two things... one, the A/C won't command the fan to come on until it's generating enough pressure (and my freon was a little low, so it never got there). Second, that the fan isn't commanded on until the coolant reaches 105 degrees, give or take. So now, my fan is on when it's supposed to be on, now that I've taken out a BAD replacement fan and put in the GOOD original fan...

The good thing is that I figured out that you CAN kinda/sorta see the fan being commanded to come on (or not) by reading the purple wire with an analog voltmeter. Figure about 1.5VDC for full on, 5.5VDC for 50%, 8.5VDC for 25%, and battery voltage for off.

Hopefully this info will help someone else down the line...