25-cent Fan Mod

[IDSmoker]

25-cent Fan Mod

The 25-cent cost estimate is probably a bit high, since this is a pic of the only part you need:



The first step is to open the hood of your LX vehicle (this mod has only been confirmed to work on 2005 Magnum RTs, but should work on all other LXs) and then find and open the fuse box.

Once the fuse box is open you must remove correct part (I think it's called a relay) which you should find here:

(Sorry for the indecipherable writing, that's what I get for using MS PaintXP, but you should be able to figure it out.)


Now you simply plug in your high-cost replacement...


If you are still unsure, here's a close-up from another angle:



Congratulations, your fan should now be running!

Since the fan will continue to run until you remove the wire, and replace it with the relay you've hopefully saved, I definitely wouldn't leave it running overnight, but it didn't cause any battery problems during the several hours I used it at the dragstrip, and it did manage to lower engine temps a good 10-20 degrees!

If you are really ambitious you can certainly use a relay, switch, and lots of wire to rig a 'safer' more permanent fan switch, but since I'm not really planning to use it outside of the dragstrip, this is good enough for me.

Enjoy!

[GoofyGuy]

Oh boy it just hit me like a train for some reason. Go to autozone get a 180 degree fan wiring kit or an adjustable and just wire it into this spot. You can control the fans to come on earler for all you guys running a cooler thermo.

[Jaak]

The mod outlined above forces one fan to high speed mode and disables the other fan for low speed mode, but still allows the FCM to enable it for high speed mode.

If you pull a different relay and put the jumper here, instead, you force both fans on, and the mode is controlled by the FCM. So they will go low speed, or high speed, as determined by the FCM, but never off.



If you want both fans on high speed mode, then you must pull three relays and put in three jumpers as shown here. Make sure you use wire that can handle the current of the fan in high speed mode. (e.g. 12 gauge)



It's a simple mod, just like the original outlined above, but requires three jumpers. The next step is to actually wire in a three position switch to do this from inside. Easy....

I apologise if I've driven this up over the 25 cent level...

[ZMagnum]

I've jumpered the relay as shown in jaaks first picture. It works fine. Both fans are on low but I did get a CEL (0480) after I started up. I cleared it by pulling fuse 11 for a few mins. No big deal at all.

Edit - Fan codes you might see:
DTC P0480 Cooling Fan Relay 1 Control Circuit
DTC P0481 Cooling Fan Relay 2 Control Circuit
DTC P0482 Cooling Fan 3 Control Circuit Malfunction
DTC P0483 Cooling Fan Rationality Check Malfunction
DTC P0484 Cooling Fan Circuit Over Current
DTC P0485 Cooling Fan Power/Ground Circuit Malfunction

[Jaak]

• When Monitored:
  • With the ignition on. Battery voltage greater than 10 volts.
• Set Condition:
  • An open or shorted circuit is detected in the radiator fan relay control circuit. One Trip Fault. Three good trips to turn off the MIL.

This is because the FCM monitors the relay coils to detect a fault. The first version of the modification, only removes one of two relays that are in parallel, so the FCM doesn't see an open or short, due to the other relays remaining in.

Of course, the best way to do this mod is to tie in external wiring to activate this, leaving the relays intact.

A second way is to measure the coil resistance and buy some resistors around that value to put in and satisfy the FCM by faking it out in to believing the relays are installed.

[Nightshade]

Leave the relays in, find some way to energize them externally..

I am thinking that because there is no diode across the coils that we can see, there must be one on the output of the circuit going to the coil.. that would prevent any back-voltage of we were to tap into the positive leg of the coil and dump 12V onto it... what's your take on this Jaak?

any way to energize the relay without pulling it out and rewiring it? I would hate to put 12V on the coil externally just to fry an output somewhere.. mind you most likely it wouldn't allow back-current..

hmmm..

• When Monitored:
  • With the ignition on. Battery voltage greater than 10 volts.
• Set Condition:
  • An open or shorted circuit is detected in the radiator fan relay control circuit. One Trip Fault. Three good trips to turn off the MIL.

This is because the FCM monitors the relay coils to detect a fault. The first version of the modification, only removes one of two relays that are in parallel, so the FCM doesn't see an open or short, due to the other relays remaining in.

Of course, the best way to do this mod is to tie in external wiring to activate this, leaving the relays intact.

A second way is to measure the coil resistance and buy some resistors around that value to put in and satisfy the FCM by faking it out in to believing the relays are installed.

[fnkychkn]

pretty sure FCM rad fan relay drivers control low side of relay coil.

[Jaak]

Yes they do... While most of us think to switch the power, it's actually easier and more effective with electronics to switch the ground in and out.

The diode for dissappating back emf from the magnetic field in coil when it's turn off, may be built right in to the relay itself, or the FCM.

At first I thought a switch to ground to energise the relay would do it, but when I realised that the system looks to see if the relay is OK (short or open) it may see this as a fault as well. So whatever is done, the FCM has to be tricked into thinking all is well.

So it has to be determined how it measures it. There's two different states it can measure in. On or Off. And it's looking for two different conditions. Short or Open.

So how would it do any of these four different measurements? When the relay is powered on, there will be certain voltage drop seen at the FCM as well as current level. If there's an open, it will see no voltage or current. (relay pulled does this) If there's a short to ground on the power side (which seems to be the fault the service manual tests for) again, there would be no voltage or current. So one test would test for both conditions.

If it looks for a fault with the fan off, then it could be as simple as looking for a voltage on the controlling wire through the relay. An open relay = no voltage = fault. A shorted power to the relay = no voltage = fault.

Unfortunately, I won't be able to look at this as I'm getting on a plane to Chicago today. I hate it when work gets in the way of having fun!

Now one way to make this work, with the jumpers, is to make additional ones that will allow the FCM to still see the relay coils. A very short pair of jumpers with male and female spade connectors would allow the relay coil to be attached to the socket, but keep the relay out of the way so that the jumper to force the fan on, can still be inserted.

Or sacrifice relays by tearing them apart and hard wiring the switched side. Then you just pull the normal relay and insert the modded ones. Of course this drives the price way beyond 25 cents!

[ZMagnum]

I like this idea:

Now one way to make this work, with the jumpers, is to make additional ones that will allow the FCM to still see the relay coils. A very short pair of jumpers with male and female spade connectors would allow the relay coil to be attached to the socket, but keep the relay out of the way so that the jumper to force the fan on, can still be inserted.

[ZMagnum]

This works great. No CEL. A bit messy I admit. Wires could be shorter. Oh, well maybe next time.

[Jaak]

Perfect, except you can lose the middle wire on the relay. You just need the two wires to make the FCM happy that it's seeing the coil. That's the normally closed contact, and since you're bypassing the normally open and the switched contacts, with the jumper, there's no point in bothering with the normally closed contact connection.

So, I'm curious, did you affect weather patterns, suck small animals, children and newspapers on to your grill?

[ZMagnum]

I was wondering about that middle wire. That will make it that much easier. Thanks.

Yes, I created my own dust devil.

Seriously, I went to McDonalds tonight with only the "both on low" fan mod w/no CEL. 76 degrees F outside. I noticed it took longer for the engine to reach full temp but it did eventually reach it. Next time I'll try both on high.

Perfect, except you can lose the middle wire on the relay. You just need the two wires to make the FCM happy that it's seeing the coil. That's the normally closed contact, and since you're bypassing the normally open and the switched contacts, with the jumper, there's no point in bothering with the normally closed contact connection.

So, I'm curious, did you affect weather patterns, suck small animals, children and newspapers on to your grill?

[Husker]

This is what we need to do for the folks who have the SC tuners and lower temp tstats. GSM is creating a "fan only" mod to help. but they are looking at 99 bucks for it. I think you guys should create a design and sell it for 25 bucks to cover your investment in time, materials etc...

Right now with the mod, my temps will swing from 183 driving to 205 or higher in traffic..

[DanRealtor]

Be careful leaving the fans on for any length of time. At our recent get together at Speedworld, several of us (myself included) got the dreaded click click, when trying to start our cars to drag race (dead battery). After a while the fans will run the battery down.

I used to do the .25 mod. Now I have the GSM Torque & Fan Mods. $199 for both. A convenient switch for the fan, and another for the Torque Management. The difference is huge as far as TM goes. Shift at 5900 in manual now without hitting the rev limiter, and all shifts in Drive or Auto Stick are noticeably firmer and quicker.

[HEMMISSEY]

now, did anyone make a switch to turn the fan on at high speed, instead of leaving it on constent high speed? I like the mod, (and I know that it will shut off when car is turned off) but just couldn't imagin my fans working hard 247?