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2 valve
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Discussion Starter #1 (Edited)
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My Radiator fan is not turning on. I'm trying to find information on some troubleshooting procedures.

When my temperature gauge reaches about 1/2 way the engine overheats. It will only overheat while driving slowly (below ~45mph when the fan should be operating). Coolant is full, good condition, attempted to "burp" the system, but heard no air escape. Pulled the cap, coolant IS circulating.


I jumped the fan directly to the battery and it operates perfectly.
I'm not sure where the issue is. Please correct me at any point. I need to test the engine coolant temp sensor(Pass firewall), the fan controller(under dash near fuse box) and the IRCM/CCRM(Pass fender well).
Can someone please confirm the location and testing procedures of these parts?


I have a Fluke multimeter and jumper wire for testing and know how to use it, so you don't have to break it down completely barney-style, but if you can explain what values to look for and where that'd be fantastic.

Please teach me a lesson. I have a baby due soon and I really hate to give my money to untrustworthy shops around here :baller:
 

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Check for the ground first. On my turbo car it's grounded to one of the studs holding the upper intake to the lower, but I forget where it was on the ol' '93. Sometimes it'll fall off the stud if I'm racing/beating on it enough...reminds me that I should probably solve that issue at some point :lol
 

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2 valve
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Discussion Starter #5
The IRCM has a continuity to a known ground.
wires 1&2 have ~1ohm from the IRCM to the Fan's connector Ruling out wiring to the fan.
Wires 3&4 @ the IRCM have 12VDC constant.

It looks like the only issue is that K4 (EDF Relay) is open and not closing for whatever reason. Is there a way I can manually energize K4 to check it's operation?
What triggers K4 to close? The coolant temp sending unit?

---------- Post added at 10:26 AM ---------- Previous post was at 09:57 AM ----------

From what I understand If I apply 12VDC to pin 14 of the IRCM it should energize Q2, Q5, Q6 and K4 whith should close the relay allowing the 12VDC from 3&4 to pass thru 1&2 and energize the Fan?
 

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The IRCM has a continuity to a known ground.
wires 1&2 have ~1ohm from the IRCM to the Fan's connector Ruling out wiring to the fan.
Wires 3&4 @ the IRCM have 12VDC constant.

It looks like the only issue is that K4 (EDF Relay) is open and not closing for whatever reason. Is there a way I can manually energize K4 to check it's operation?
What triggers K4 to close? The coolant temp sending unit?

---------- Post added at 10:26 AM ---------- Previous post was at 09:57 AM ----------

From what I understand If I apply 12VDC to pin 14 of the IRCM it should energize Q2, Q5, Q6 and K4 whith should close the relay allowing the 12VDC from 3&4 to pass thru 1&2 and energize the Fan?
As best I can tell, this is what should happen...

IRCM pin 14 is controlled by an output of the ECC. When the engine is below 190*, the ECC applies a "low" to pin 14. The low turns off Q2, allowing Q5 to turn on, causing Q6 to turn off. Conversely, when the ECC determines a need for the cooling fan, it removes the low from pin 14 which allows Q2 to turn on, Q5 shuts off, and Q6 turns on energising K4 and applying voltage to the main fan via IRCM pins 1 and 2. This circuit apparently acts as a kind of "failsafe" for the fan; if the ECC wire to IRCM pin 14 breaks or if the ECC output "opens", the main fan will run continuously.
It looks like if you simply applied 12 volts to pin 14, then the fan should operate based on this...

IRCM pin 14 is the control input for the primary fan. If pin 14 were open(high), R4 applies +12 volts through the R9 current limiting resistor to the base of Q2. The current flowing into the Q2 base turns it on, making the collector "low". The "low" applied to Q5's base turns Q5 off, making it's collector "high". The "high" thus applied to the base of Q6 turns Q6 on, pulling the Q6 collector low, energizing K4, thus turning on the fan.
 

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2 valve
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82 Posts
Discussion Starter #8
Applied 12VDC to pin 14 of the IRCM. Pin 14 controls the primary fan circuit. The good news is that the fan turned on, but didn't stop until I turned off the ignition. I restarted the engine and the Fan did not come back on. I'm pretty sure it's down to the coolant temp sending unit or possibly the Fan controller

Sending unit located in a hose on the pass-side firewall

Duralast/Cooling Fan Switch - Radiator (SU201) | AutoZone.com


Located under the driver's dashboard attached to Fuse box

Murray Climate Control 37506 - Radiator Fan Controller Relay | O'Reilly Auto Parts

---------- Post added at 04:35 PM ---------- Previous post was at 04:34 PM ----------

I'm very seriously suspecting the Sending unit due to the fact that My temp gauge isn't working correctly

---------- Post added at 04:47 PM ---------- Previous post was at 04:35 PM ----------
 

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It doesn't use the sending unit for your gauge to turn on. It uses the Temp sensor that the computer sees to turn on and off. It is computer controlled, not controlled by an idiot switch.
What is more than likely happening is that you are not used to the high temps it requires for the fan to turn on. Mine does not turn on until the temp needle is about 3/4's to 7/8's up the scale, which comes out to 205 degrees. That is the factory setting in the computer for fan on. It will turn off at 198 or something close, can't remember off hand. I set mine down to 190 kick on temp, and it still never comes on due to my large aftermarket radiator.

Now, if the car has a/c, it should come on when the a/c is turned on as well and is not temp dependent at that point.
 

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2 valve
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Discussion Starter #10
The car is back up and running. Ended up being the "Cooling Fan Switch". The gauge now reads when the engine warms up and the fan turns on when the engine reaches a little over 1/2 way up the gauge. <$20 part with a lifetime warranty so if it ever happens again, I'm covered =) YAY!

Thanks for the help. The wiring schematics really helped.
 

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The car is back up and running. Ended up being the "Cooling Fan Switch". The gauge now reads when the engine warms up and the fan turns on when the engine reaches a little over 1/2 way up the gauge. <$20 part with a lifetime warranty so if it ever happens again, I'm covered =) YAY!

Thanks for the help. The wiring schematics really helped.
i know old thread but im experiencing same issue too on my 93. right now i have fan wired to a toggle switch. i wanna fix it right, so what was the part you replaced? the one mounted on the heater hose? on on the driver side of the head? i already replaced my IRCM and jumped the fan to the battery only thing i did not replace was the one on the head. my fan does not turn on when i turn the a/c on so i know there is a problem
 
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