Originally Posted by
Romad
The radiator fan is SIMPLE:
FOUND THIS QUOTE FROM PIZZAGUY, MAR 22/2014
The PTCM communicates it's desire for the fan to run over a single wire, bidirectional, Pulse Width Modulated data stream. When the PTCM wants the fan to run, it "tells" the Fan Control Module to speed it up. There is a two-way pulse sent back and forth, the PTCM 'pings' the FCM and the FCM pings back, indicating all is well.
If the communications break down between the FCM and the PTCM, two things happen:
1) The PTCM alerts you to a possible cooling system failure by turning on a small yellow indicator to the side of the instrument panel, it looks like a little radiator.
2) The FCM goes into "emergency mode" and spins the fan at high speed.
If you do NOT have the little light, it would imply that the ECU is corrupt/bad. But I've never seen this happen - Pizzaguy
If you DO have the light, you have a bad connection between the two modules or a broken wire. or a bad Fan module. - Pizzaguy
The PTCM COULD be bad, but this would be a "first" that I've heard of in over four years on this forum. FCMs go bad kinda often.
PIZZAGUY: WHERE IS THIS LITTLE LIGHT YOU SPEAK OF? I'm guessing it's the radiator light on the dash panel! I just ordered the FCM cause my light does "not" turn on when fans ramp up high. ( Best hunch right now. )
The light is the "Low Coolant" light, that is, the little "radiator light" on the left side of the instrument panel with several other indicators (to the left of the speedo).
See my edits in
bold RED.