Blk Beauty

I know that this has been an issue and has been discussed at length. Over the last couple of months I have had to bypass the known to melt plug one wire at a time. Still in tact is the thin PWM wire. Well as of today fan is not coming on again. All my connections look fine. The large plug that connects to the control box is getting power on the second pin. I am able to jump the fan by using 2 short pieces of wire.

The PWM wire pins look fine at the smaller melted female connector. All that I can think of is the control box is bad. Has anyone had to bypass the PWM wire? Im so tired of this crap I am thinking of just wiring the fan to an ignition on power source. Not sure where to do that at though.

YELP!

RicK T

I know this doesn't help but you'd probably get more help in the Tech Forum. Good luck, I'm sure there's an answer here someplace.

Blk Beauty

thanks for the advice, rather than starting another thread hopefully a moderator can move this to that sub forum.

BlindSpot

The fan control module works like a giant solid state relay that converts a low amp pulsed signal into a high amp variable voltage. If you have tested the fan itself by jumpering the FCM connector (two reds and two blacks) then the next test is the 18 ga signal wire coming from the ECM.

This signal wire completes a ground. The ECM sends that signal at variable pulse rates based on fan % commanded. The FCM can be tested using a needle probe with a lead. Just probe the 18ga wire at the connector (plugged in) at the FCM then simulate a ground pulse on a good ground sight. If the fan runs or tries to run based on the pulses you simulate, then the fan control module is good (they do fail though).

If the FCM is good, then the three most common problems are:

The signal wire - check continuity from the FCM connector all the way back to the ECM connector

Bad ECM - This is known to fail too.

Weak or failed ground - the fan control uses the ground lug on the passenger's side, high on the frame rail in the engine compartment, can be seen from the top with the hood opened.

All this said - I am assuming you have the factory tune and no one has intervened and changed the fan settings in the tune?

And, you're still seeing ECTs high enough the fan should be running - In Houston I am guessing you are.

Not So Fast

Steveo to the rescue
NSF

Blk Beauty

Thanks for the info, turns out the control module was bad. Back in business.

BlindSpot

Good to hear!

This fan design is overly complex and GM really didn't do a very good job IMO. This circuit is light on wire gauges. Then, to keep fuses from popping they specced a 60 amp fuse. That is one of the cuplrits leading to the melted connectors. Then the signal wire is too fragile. But GM is notorious for under designing wiring, all the way back to the 50s.

All that said, Most other car mfgrs are using similar designs. Everything today is about the engine management system basically controlling everything.