Fan question

[SHOtgun1]

First off, I'd just like to say how helpful this website has been for diagnosing problems with my '95 Red/Mocha MTX SHO!

However, I seem to have run into a problem where my mechanical knowledge is failing me (not that I have much!). About three months ago my engine fan motor failed and, in turn, was replaced with a new one which worked just fine up until a few days ago. Here's when things got a little tricky for me, I noticed that my temperature gauge was reading quite hot. So, I pulled over and checked to see what the problem seemed to be. After spending way too much time looking for a smaller problem, I noticed that my fan was, again, not working. I have checked the majority of the connections leading to the fan motor and to the harness above the radiator, and everything seems to be fine. The only time I can get the fan to engage is when I run the A/C, namely from a cold start. The fan does spin freely for whatever that is worth.

If anyone has any suggestions of things that this could be, I would appreciate any help as it seems the majority of mechanics in this town think that my SHO is a mustang!

Anyhow, sorry to ramble on my first post, but again, great site!

 

[Ishodu]

The temp gauges can be quite misleading sometimes, some cars will need to be 2/3rds the way to red before the fan will come on. How high is quite hot?

 

[fusion1620]

Could be the sensor that is located to the right of the temp sensor. That is what controls the fan from what I've heard.

The gauge and the computer uses completely different sensors.

You have two: The single wire sensor is for the gauge, the two-wire one (ECT) is used by the computer to control, among other things, the cooling fan.

Steve

 

[SolidState]

on a properly functioning stock gauge, the 'A' is about 190 degrees, and the 'O' is about 220 degrees. The ECU signals the IRCM (or CCRM, depending on year) to turn the high-speed fan on at 220 degrees.

The ECU gets its signal from the ECT, which is located below the rear cylinder head on the drivers side. The gauge sender is just below the thermostat.

If the gauge is functioning properly, the next step would be to change the ECT. If it still doesn't work properly, try giving the IRCM a good whack. Testing the fans is pretty simple. Wire them up to 12v source.

 

[SHOZ123]

The fan is a two speed motor. Could be both low speeds are burnt out, unlikely but. Apply power directly to the Brown/Orange wire and the fan should turn on at low speed.

If the Tan/Orange wire going to the PCM is sending power to the CCRM (this may also be a ground) then the PCM is telling the CCRM low speed fan relay to come on and power should be going out to the fans on the Br/O wires.

 

[projectSHO89]

The fan on the 94 & 95 MTX (may apply to others, I haven't checked) is run ONLY in LOW speed under the control of the PCM. HIGH speed can only be engaged if the A/C system refrigerant containment switch trips due to an over pressure in that system. The PCM has no control over the HIGH speed portion of the circuit.

The CCRM contains two relays of interest to this discussion: The LOW and HIGH speed relays. The LOW speed relays fail over time due to continuous usage over the life of the module.

There is an easy test that can be performed to test the relay for operation. Use a meter test lead and connect one end (the meter side) to chassis ground. With the ignition set to RUN, backprobe the CCRM connector pin 14 TAN/ORANGE. The internal relay should energize and the fan motor should run at low speed. Similarly, the high speed function can be tested by performing the same operation on pin 17 PINK/LT BLUE.

Specific details on the CCRM can be found in the stickied post titled IRCM/CCRM Details located in the Electronics sub-form. Pinouts and a full operational description are included, just sort through the other stuff.

As noted, the stock sending unit and gauge are well known to not be very accurate. A second source of data such as an IR thermometer or a thermocouple is highly recommended to verify actual temperatures whenever a concern about "too warm" is being investigated.

Steve

 

[SHOtgun1]

My apologies about the slow response time, finals and all that good junk are taking up the majority of my time.

In response to -Ishodu- about how hot "quite hot" is, the temp gauge is through the roof, the gauge will climb as high as the needle allows it, but upon activating the A/C it will level out. This only appears to be happening at stop & go traffic, but has been become a bigger issue as it has been warming up quite a bit around here.

In regards to the IRCM/CCRM, I will definately check that as that could, indeed, help me to troubleSHOot.

Anyhow, thanks for the help guys!