High speed fan issue.

[dodgefever]

I didn't want to hijack Cayman's thread with this, although we have a similar problem.

I noticed on Friday when the temp outside was about 90 Degrees, the temp on the gauge was getting up to the 220 mark in traffic. On the highway it was down to 190. Fluid level is good. I noticed with the A.C. on, the fan was staying in the low speed setting, no matter how high the temp. got.
I swapped the two fan relay's and still got no high speed fan. I did notice this though...

As you can see, terminal port 87 for the high speed fan relay is cooked. Double click pics to make bigger.


A comparison of the two relay ports.


A pic showing relay spade 87 appears to be fine.


How do I remove the cover from the terminal block to inspect the wiring below?
What are the parameters that make the high speed fan kick in?

 

[dave6666]

Those things are usually not meant to be taken apart, but it looks like in the pic you may be able to work the outer black plastic away and pull the red portion up and away. And then if you do get inside good luck finding a way to fix it.

I had the main fuse panel on my Super Duty burn up and I did an autopsy on it just for fun. It had 6 layers of bussing and circuitry in that box.

 

[Tom F&L GoR]

Ugh. You might be better off intercepting the wires leading to the fan relays in the block, cutting them and reconstructing those wires for the relays outside of the block.

The PCM logic decides when to turn the fans on high or low speed, based on the temp sensor dedicated to the PCM (does not use the temp gauge sensor.)

 

[bumblebee]

were are those relays located?
my fan is not turning on,only if ac on. I have 02 gts.
Thanks.

 

[dave6666]

were are those relays located?
my fan is not turning on,only if ac on. I have 02 gts.
Thanks.

Under the hood driver side above the footwell by the brake master cylinder booster.

Photo courtesy of Big Brakes...

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[dodgefever]

After a little more troubleshooting, I discovered my overflow bottle was empty. dave6666, thanks for the write up on how to fill that. After a "spirited" drive for about an hour, it never hit 220. I did see it climb and then drop quickly, like it may need to be burped. What's the best way to do that?

 

[cayman]

were are those relays located?
my fan is not turning on,only if ac on. I have 02 gts.
Thanks.

Bumblebee,
You might try this troubleshooting routine from a previous post of mine:

Fan relays check out fine. I manually shorted them out through the pin connector off of the pcm. I found this to be the best way as you are checking the wiring all the way from the pcm, through the relays and to the fan. Pin 2 goes to one side of the coil on the ON relay and pin 21 is for the HI/LO relay. Shorting out pin 2 to ground kicks the fan on low. Simultaneousy shorting that pin and pin 21 both to ground, will kick the fan on HI mode. BTW, you have to have the ignition switch on for the HI/LO relay to work as the other side of the coil on that relay is wired through the ignition B+.

The pcm grounds out one side of the coil to the ON relay at 207 degrees and then the HI/LO relay kicks the fan in to hi mode at 216, according to the service manual. I can only extrapolate the gage reading since its not linear and there are no corresponding temperature numbers for the hash mark between 190 and 250 but I have to assume that mark is around 205 to 210.

Also, for anyone else's tidbit info, there is only one temp sensor on the gen II's. The sensor has two elements. One feeds the temp gage and the other feeds a signal back to the pcm, which in turn, uses that signal to, among other things, turn the fan on low or hi based on the temp signal.

 

[dave6666]

I did see it climb and then drop quickly...

You'll get dizzy watching my gauge go up and down.

The Gen 2 cooling system is self purging of air to a degree. Certainly takes a well maintained system to start with though. I have the Roe vented hose and after filling do nothing but keep an eye on the fascia bottle. Works here in this heat

 

[dodgefever]

I forgot the most important piece of info... I swapped the two relays since they are the same part number. Now the high speed fan comes on AND I tripped a code P1490 which I understand to mean low speed fan issues. So, it seems I do have a bad relay.