2003 Town Car Signature - Cooling Fan Logic

[jsoluna]

Hey all,

My cooling fan kicks on at about 22% duty cycle and remains in that mode. According to the scantool, the PCM is not requesting a high or a low speed for the fan. A/C is not requested, and as you can see, the engine is not even up to operating temp yet.

How is the logic supposed to work for the cooling fan?

 

[Town]

That is a nice readout, but is FANVAR referring to the blower fan or the engine cooling fan. The PCM controls the engine cooling fan and that is not activated until the A/C is turned on or the engine coolant is over temperature. So you have a cooling fan module failure or some such problem.

The EATC controls the HVAC blower fan and is programmed to not allow the blower fan on until engine coolant is up to a minimum temperature and then it progressively increases blower fan speed according to ambient temperature and cabin temperature setting(s). The EATC also controls the recirc door to stay closed when engine is cold in heat mode or in A/C mode until interior is cooled somewhat close to temp setting. EATC opens the recirc door when heat or A/C parameters are reached to manage humidity levels and maximise fresh air levels and comfort. Your engine appears hot enough to get the blower fan operating, so the blower speed should increase gradually to max speed (if ambient temp is cold enough). If it never achieves high blower speed then the BMSC (blower motor speed control) is likely not functioning correctly.

We have a procedure in out Tech forum here: Town Car BMSC Blower Motor Speed Control replacement to help with diagnosing the BMSC and replacing it. On the 2003 and up the cooling system must be drained, so spending time diagnosing the problem is a good idea.

Good luck.

 

[jsoluna]

Thanks Town!

To be clear, the issue I have is indeed with the engine cooling fan, not the EATC/HVAC blower fan.

Looks like a three wire connection to the fan control module, located directly on the housing.

I assume the two large wires are for fan voltage supply to the module, and the smaller wire is the fan speed sensing wire that PCM monitors?

Faulty module would explain why the fan is operating without PCM request.

 

[Town]

I presume that the fan is actually turning and you checked it? If so then the module can be replaced. The FANVAR_F says "No Fault" so what does that mean, that the dasboard circuits are good or the car's electronics are good?

I think your wire descriptions are correct, but the small wire is the signal wire that the PCM uses to tell the module what to do. I have a wiring diagram for that circuit that I posted a little while ago. I will find it or re-post it after lunch.

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[jsoluna]

I presume that the fan is actually turning and you checked it? If so then the module can be replaced. The FANVAR_F says "No Fault" so what does that mean, that the dasboard circuits are good or the car's electronics are good?

I think your wire descriptions are correct, but the small wire is the signal wire that the PCM uses to tell the module what to do. I have a wiring diagram for that circuit that I posted a little while ago. I will find it or re-post it after lunch.

I did check the fan, yes and the ~22% duty cycle seen by PCM corresponds roughly to the speed of the fan, which is always on when engine is running.

If the small wire is an ouput from PCM to tell the module what speed to run the fans at, then maybe the PCM is commanding the request? Or are there only two speeds, high and low?

The parameters on the display are all the ones available via PCM PID, so a fault, a high, a low, and a variable value.

 

[jsoluna]

Just had a thought-if I remove the signal out/signal in wire but leave the main power supply wires connected and the fan still operates at all times, then that would tell me if it is indeed within the module itself.

Proper diagnosis would be to confirm the pinout and control logic though.

 

[Town]

I think the cooling fan is a variable speed fan rather than a 2 speed fan. The module is likely the culprit but I don't know how to verify that the PCM is acting correctly as opposed to the module electronics failing and setting a speed approximating a low speed operation.

The cooling fan circuit has the pinout for the PCM, I think.

 

[jsoluna]

It's a relatively simple control circuit. Hopefully the wiring diagram gives me a clue to the proper operation as well as the pinouts.

A ladder diagram would be awesome for something like this.

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[Town]

Is the defroster off? that is HVAC EATC in a position other than defrost?

 

[jsoluna]

I'm wondering if this is just proper programmed operation.

Removed the wire from the 3 pin socket that signals the control module to vary fan speed. Reconnected. Retested:

1. Fan did not operate.
2. PCM can see fan fault.
3. Commanded duty cycle remained the same.
4. Cycled A/C and commanded duty cycle went to 35%.
5. Duty cycle command dropped back to 22% after A/C was cycled off.

*Edit* all of my base testing is done without any request for defrost or A/C. Even turned HAVC mode to OFF completely to confirm.

 

[jsoluna]

I'm thinking that if it is proper operation to have fan always on at a low duty cycle that it might mimic a clutched fan, which doesn't every truly stop.

 

[Town]

Your condition is "fan runs at all times with A/C off and defrost off and engine cool" that is a problem condition. So you have:
1. cooling fan control module failure;
2. A/C pressure switch failure;
3. Cooling system (likely temp sender unit) failure;
4. PCM failure for which there are self tests with the right equipment.

The problem is likely in the cooling fan control module. Still looking for the wiring diagram.

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[jsoluna]

Your condition is "fan runs at all times with A/C off and defrost off and engine cool" that is a problem condition. So you have:
1. cooling fan control module failure;
2. A/C pressure switch failure;
3. Cooling system (likely temp sender unit) failure;
4. PCM failure for which there are self tests with the right equipment.

The problem is likely in the cooling fan control module. Still looking for the wiring diagram.

Ran some self tests for various systems including PCM, which has a persistent P1000 code (readiness monitors) and a VSS code and a SCP data/instrument cluster code.

I also ran output tests for cooling fan, and it was able to turn it on and off, but that tells me very little.

The strange thing I think is that the fan is requested on regardless, which makes me think the module for the fan is fine since it isn't "smart" enough to request itself on/off. PCM self tests (both engine on and engine off) completed just fine.

Is there a factory service manual that I could find that would describe all the control/failure conditions for the cooling fan circuit?

 

[Town]

The 2007 Ford service manual for the 2006 & 2007 Lincoln Town Car only describes the operation of the viscous clutch cooling fan. It says to go to the PC/ED (Powertrain control and emission diagnostics) manual for the electronic control of the cooling fan. The procedures there relate to a 3 relay system with accessible relays controlled by the PCM. This is like the 2002 and earlier systems with a low and high speed fan circuit where there is a relay for each that is individually controlled by the PCM. However the 2007 and presumeably the 2003 and up use a variable speed cooling fan system where the PCM directs the speed by a signal wire to the fan control module. The fan control module has internal relays that individually or in combination set the cooling fan speed.

I have not yet found the variable speed control info in the PC/ED manual. I have not yet found cell 33 for the 2007 cooling fan electrical circuits. Here attached is the 2001 cell 33 cooling fan circuits, a 2 speed system.

 

[jsoluna]

That is a nice and simple control system!

I personally think this PWM control setup is overkill on my '03.

Check out this video, guy goes pretty deep into this system. Not the same problem as I have, but diagnosis of the same system.

 

[Town]

I think it is the same problem. On the later models the fan module is replaceable, but for the 2003 it appears you have to replace the fan assembly which includes the fan module. Here is the range of suppliers and their Canadian prices ($123 thru $269) for the fan assembly: https://www.rockauto.com/en/catalog/lincoln,2003,town+car,4.6l+v8,1410714,cooling+system so US prices should be much lower.

What makes you think the problem is elsewhere?

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[jsoluna]

The main reason I think it is a different issue in my case is that the request for duty cycle never drops to zero for me. Since the fan module can't "decide" and only knows what it is told via the voltage reference from PCM, then I can't in theory condemn it since the "FAN_VAR" PID request never asks for 0% duty cycle.

Also, though not a further illustration of that line of logic, my fan does not run if until engine is started. In that video, the fan ran at all times.

I checked more sensors and inputs and from what I can tell the PCM should not request the fans to come on at all.

I may have to invest in a service and electrical diagnosis manual to understand all the conditions under which PCM can request the cooling fan duty cycle.

 

[jsoluna]

This is not to say that the fan module isn't bad - I do agree it is the most likely culprit.

These Lincolns and their modules will give your diagnostic brain a workout.

From what I understand, that smaller wire both provides a 12v reference to the PCM, which is then pulled down by PCM, which gives the fan control module a signal for what speed to vary the fan at. It is both an input and an ouput simultaneously.

 

[Town]

From what I remember of the 40 minute video last night is that the fan is powered all the time, but the ignition was turned on to get the fan to run. I think this is the same condition as you are experiencing. In your first post you said the scantool is not showing the PCM requesting a high or low fan speed. I think this is the same condition shown in the video.

The factors affecting the PCM turning on the fan are as noted previously: A/C requested on, defroster on, cooling system (i.e. temp sensor indicating high temp); A/C pressure switch indicating high pressure. The fan is a variable speed device and the sensor wire carries the signal to accomplish this but I have no idea how this is achieved. The video was as much a learning tool for the person directing it as for me as the student. So it is not at all clear how the PCM accomplishes this magic. What was very clear once the fan motor and module were replaced was that the fan speed was being varied, but no explanation of how this was accomplished. Perhaps I should re-visit the video.

So in the absence of any info from your scantool that the PCM is commanding the fan on, I think the problem is with the module which is not available separately from the fan assembly. Just my thoughts on your problem, I am no expert.

 

[jsoluna]

You may be correct about the ignition on/run condition in the video. I will revisit it as well.

I am no expert either, and greatly appreciate both your willingness to assist and your rational approach to the subject. Too often on forums people are looking for a quick fix or an answer and are not interested in problem solving.

My plan for now is to look at my data and self tests in the full featured ForScan on my laptop (up until this point it has all been done on mobile).

I am also going to purchase some proper service documentation so that we can better understand the operation and logic.

I will help contribute to the forum as best I can in this endeavor.