Radiator Fans only working with A/C on

[XfireZ51]

So take the pin for the ECM ground to the fans and ground it. See if the fans turn on. Basically, grounding the A/B ALDL pins will tell you the same thing.

[XfireZ51]

Originally Posted by Franke

Interesting info XfireZ51. 112Centi is 233 degrees farenheit and 114Centi is 237. I'm trying to understand why so high before fan request without AC. Is it possible maybe these bin values are modified somewhere else by other ECM inputs to lower the fan turn on request?

I have Marcs chip in my ECM and did see that the fans acted just as Dynomite says.

No. Likely this was done to keep exhaust hot for cats. I just installed a Fluidyne rad. If I don't raise the fan request temps, CTS drops below temp where ECM LEARNS for updating BLMs.

[WVZR-1]

Originally Posted by XfireZ51

So take the pin for the ECM ground to the fans and ground it. See if the fans turn on. Basically, grounding the A/B ALDL pins will tell you the same thing.

No I believe you would ground the relay directly to confirm fan operation, return everything to correct wired scheme and then supply required resistance to the CTS connector to confirm that the ECM ground is being switched when the correct resistance is being seen by the ECM.