2005 Ford Escape PCM Relay Overheating

cherylmitcherylmit Member Posts: 4
edited September 2016 in Ford
@thecardoc3 , you are the person who knows how to use test equipment. I have been having the same problems as I've read about with my Escape but I know it runs way too good for it to have all these major issues that people are told it has. No plugs or coils burnt up, no PCM fried, no new engine needed. None of the multitude of expensive repairs people are getting that don't solve the problem. My Escape runs like a champ. I'd drive it across the country. As long as the OUTSIDE temp. is less than 75 deg. For OVER 2 YEARS I've been trying to determine the real reason for the sudden quitting and the other symptoms that go along with it. I drive it 60 miles when it's 75-80+ degrees outside and it quits. Over and over.....It's taken 5 hours for me to drive 40 miles. (more than once!) In June it went 150 miles before it quit while towing a small pop-up camper. I had to leave the camper, drive home and get the F150, that gets 17 mpg. Last year, determined not to give up it took 16 hours to make a 9 hour drive, again, towing the camper. Yesterday, 70 something miles from home, on the side of the Interstate and 95 degrees outside it quit and I decided to experiment. I had my lunch with me, a freeze pack in my bag so... It feels like I run out of gas so I felt all my relays and they were ALL hot as a pistol but the fuel pump relay felt the hottest so I swapped out that relay with a spare I had with me and away I went. Are you kidding!? OK, I went about 10 miles and quit. I felt the relays, the PCM relay felt the hottest so I swapped it out for another relay I had with me. (I have narrowed it down to an ambient temperature, overheating of something electrical, relay, sensor, SOMETHING electrical related, so I had extra relays.) Now I start up and away I go! Let me interject here, I have the high speed fan relay jumpered so that it is on all the time. And the cat. has been removed, and I do not use the AC, or the cruise. Another 15 miles and it quits and I swap out the PCM relay again and I decide to lay my freeze pack on top of the relays to keep them cool. I managed with some electrical tape and drove away. NO problems. It quit after about 20 miles. I felt the relays and they were all nice and cool EXCEPT the PCM relay. It was hot hot. I swapped it out for a cool one and drove away. No problems. OMG! It quit after about 15 miles. I checked the relays, all nice and cool except the PCM, it was hot as hell. I swapped it for a cool one and drove away and this was the pattern all the way home, 15 to 20 miles and quit, swap, and drive. I went the back way so I didn't have to drive as fast and there were safer places to pull off. It'll coast pretty far in neutral. I can drive the 20 miles to work in the heat at 55-65 mph and go through the 5 lights in town without quitting but I cannot rely on it to go any distance. I can't wait for the cool days of Fall to get here so I will have no concerns about getting killed on the highways. I'm going to invent a way to keep that PCM relay cool while hopefully, Cardoc3, YOU can figure out why the PCM relay is overheating. I will leave it to you.

Best Answer


  • thecardoc3thecardoc3 Member Posts: 5,559
    The first thing to do is to restore proper high speed fan operation. The fan does not need to be running once you are over 25mph. At that speed and higher, there is more air being pushed through the radiator by moving down the road than the fan would ever pull. The fan running all of the time just wastes fuel and will contribute to your alternator wearing out quicker.

    While relays can get warm with normal operation, trying to decide what is too hot by feel alone is going to be too subjective and as you have seen just trying to swap them out or keep them cool hasn't been successful towards solving this issue. To figure out a problem like this when one occurs, you have to first find out what you are losing, such as spark, fuel pressure or injection pulse (or some combination of them) and then from there, prove why they are being lost.

    For instance if you are losing spark, it could be a problem with source voltage for the coils, the command circuits (which does include the PCM) or it could be an input issue for the PCM. This is why a multiple channel digital oscilloscope is such an important tool, it allows the tech to monitor the inputs to the computer as well as the outputs from it simultaneously. The fact that this failure is so random does make a problem like this more difficult to catch, but it might not have to be driven to get it to act up. I would try to have all of the test equipment hooked up and just let the engine and accessories run while doing other work all the while being prepared to attack the problem should it occur.

    Has anyone ever experienced the symptom while a scan tool was connected and recorded the data before and during the event? Are there any codes setting? Keep in mind swapping relays could generate false codes....
  • cherylmitcherylmit Member Posts: 4
    thecardoc3, I'll put the fan relay back in, I see your point. As to the relays, it is not subjective, the PCM relay is so hot that the spades will cause a burn. If you felt the difference between the cool ones and that one, we're talking dangerously hot, like possible combustion hot. And the fact that swapping out with a spare allowed me to start and run, which it would not do on any of the other occasions, (I had to sit and wait for it to cool down every 2 or 3 miles), is what has me convinced that it is the PCM relay only. I did leave it with my mechanic and asked him to keep it and drive it for as long as he needed in order to figure out what's going on. Well, he doesn't have the experience with electrical issues that you have. I wish every mechanic had to be trained by you. My problem understanding what is going on is the darn thing runs so well. It never misses or hesitates, ever. Even when it's quitting repeatedly. It just feels like it runs out of fuel, no power, coast, and then engine stops, dash lights come on and it won't restart. I can detect a slight loss of power just before it quits (after all my previous experiences) which gives me a tiny bit of time to prepare to pull off. I'll talk to my mechanic about hooking up an oscilloscope and if he doesn't have the right equipment, I'll find someone who does. Oh, I read that the coolant sensor for the PCM is located above the transaxle bell housing. Possible problem there? Could it be a ground issue? Whatever it is, it is related to the ambient temp. I really appreciate your help and I'll let you know what I find out.
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