Engine fan doesn't start. PCM defect?

[fivepulse]

Hello everyone,

I'm from Germany, where not many people are familiar with the control unit of a Mustang. So I'm hoping you can help me!

I have the following problems:

-The coolant is boiling over.
Cause: The engine fan is not starting.

-Sometimes the engine stalls when idling, but only when the air conditioning is on.

-Cruise control is not working (not important, but perhaps relevant for troubleshooting).

I have found out the following so far:

When the air conditioning is turned on, the engine fan also starts.
Without air conditioning, the fan does not start at all, even at 110°C.

The two fuses for the fan relays are intact.

The two relays for the two fan speeds also work (cross-checked with horn relay).

The engine fan itself also rotates at both speeds when connected directly to the 12V battery.

The temperature sensor provides plausible readings.

The coolant circulates (both hoses get hot).

Therefore, I believe that the PCM could be the cause.

Background information on the car:

2006 Ford Mustang GT 4.6L

I purchased the vehicle from an importer six years ago.
At that time, the car was converted to EU standards, which means yellow turn signals, etc.

The company did a poor job at the time; the brake light was branched off from the third (middle) brake light, and shortly afterwards I had a permanent brake light and no cruise control. A cable including a relay was then laid from the brake light switch, thus solving the problem. However, I have not had cruise control since then, and I recently noticed that the engine gets much too hot.

There is no error in the ECU when I read it.

I removed and opened the PCM because I suspected something was wrong. I was hoping to find an obviously defective component, but all the soldering and components look fine.

It would be good if I could test the PCM somehow. Repairs and refurbished parts are only available in the US, with shipping costs to Germany amounting to $300. That's why I want to be sure before I order anything.

I am very grateful for ideas and tips.

Best regards,
Luca

 

[StockishS197]

The #1 reason for fans not running on these cars is a melted fuse box/BEC. Even if from the top the relay and BEC look OK, you should really separate the fuse box into its two pieces (it’s held together by two bolts). The damage can be to the pins on the lower connections for the high speed relay. That’s the first thing I would check. Just be careful when putting the two halves together you don’t bend any pins and don’t over tighten.

If all that looks good, then you would need to see if the PCM is commanding low/high speed. You can check that either by logging or providing the fuse block with a multi meter to ensure the relays are getting power.

If that checks out, and if the fan isn’t coming on low or high, a close second most common cause of no fan is a melted fan plug connection on the fan itself. The plug is fairly easy to get to and you can separate those two to inspect there.

 

[fivepulse]

The #1 reason for fans not running on these cars is a melted fuse box/BEC. Even if from the top the relay and BEC look OK, you should really separate the fuse box into its two pieces (it’s held together by two bolts). The damage can be to the pins on the lower connections for the high speed relay. That’s the first thing I would check. Just be careful when putting the two halves together you don’t bend any pins and don’t over tighten.

If all that looks good, then you would need to see if the PCM is commanding low/high speed. You can check that either by logging or providing the fuse block with a multi meter to ensure the relays are getting power.

If that checks out, and if the fan isn’t coming on low or high, a close second most common cause of no fan is a melted fan plug connection on the fan itself. The plug is fairly easy to get to and you can separate those two to inspect there.

Hi, thank you very much for your help. I disassembled and inspected the fuse box and the PCM. Everything looked great, no damage, no melted plastic. Before reassembling, I sprayed all contacts and pins with contact spray (wd40)—now everything is working, the fan turns on at approx. 102°C/215°F and cools the engine down.

 

[brasil]

...even if the fan is working now. I would highly recommend to put some relays in betweeen the wiring from the fuse box to the radiator fan. sooner or later the tiny wires will start to make issues.

 

[DieHarder]

The fan is ~20 years old. As electrical motors age they draw more current than when new adding to the problem of the wiring being too thin to carry the current load... It's a good idea to replace it with a 7-blade GT500 fan and replace the wiring loom with that aftermarket version I've seen on the forum at the same time. Cheap insurance in the long run.

 

[Dino Dino Bambino]

The fan is ~20 years old. As electrical motors age they draw more current than when new adding to the problem of the wiring being too thin to carry the current load... It would be a good idea to replace it with a 7-blade GT500 fan and replace the wiring loom with that aftermarket version I've seen on the forum at the same time. Cheap insurance in the long run.

Excellent advice!
@fivepulse be proactive and buy a new GT500 fan together with the modified fan resistor pack in this link:

Modified Fan Resistor Pack for Ford Racing Fan or 13/14 GT500

STOP BURING FAN CIRCUITS! Introducing the FRPP (Ford Racing) or 2013-14 GT500 Modified Fan Resistor Pack - a high-quality wiring solution for your vehicle's cooling system. Simply remove your existing resistor pack form the fan assembly and swap in the Wire Everything modified resistor pack...

wireeverything.com

I know it's a lot of money but it's better than risking the engine overheating in slow traffic, warping the cylinder heads, and blowing a head gasket.

 

[brasil]

I ordered the wiring wirh relais from. wireeverything

Works like a charme !! Highly recomended in my opinion.

Together with the 7 blade fan , it is a bullitt proof set up