Question about 1999 Ford Taurus

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PCM Is there anyway to test a PCM to see if it's bad before taking it to the dealer? I want to make sure that the PCM is bad before I go about changing out the unit. I'm having a problem with hesitation as the car gets warmer and warmer, and the cooling fans only operate with the CTS disconnected (they operate the entire time the engine is engaged). Previously I have had problems with the radio acting "wacky" i.e. randomly tuning, switching bands, draining the battery. The tachometer doesn't work reliably either. Does this all sound like a PCM going out, or is it more likely that it is a myriad of different issues? Any help would be appreciated. It's a 1999 Ford Taurus SE with a 12-valve 3.0L OHV Vulcan engine-automatic tranny.

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  • 13 more comments 
  • Joseph Weisenberger
    Joseph Weisenberger Jun 22, 2009

    Car hasn't been involved in a crash, but it had overheated. I had to replace the head gaskets, one cylinder head, all the gaskets, timing chain, coolant temp sensor, radiator cap, thermostat, etc. I have by-passed the heater core as well. The strange thing is that the cooling fans don't work unless the CTS is unplugged. This seems to be the root issue, and I've checked the relay. There is no water entry in the passenger compartment at all, nor have I seen any loose connections or stripped wires. So the fans running continuously while the CTS is unplugged is just a default setting to protect the engine?

  • Joseph Weisenberger
    Joseph Weisenberger Jun 22, 2009

    The only after market products installed are OEM compliant. The strange thing about this is that the cooling fans worked for quite awhile. I had continuous problems with overflowing coolant (it would not boil or steam, just overflow). The radiator is verified to be working, but the cooling fans just don't come on. I have done a block test, which came up negative for combustion/emissions gasses, and nearly everything in the cooling system (other than the radiator) is new. After replacing the radiator cap, the system ceased overflowing for about a week and a half, then the cooling fans seem to have stopped. The CTS was bad, so I replaced it, but the cooling fans still don't come on unless the sensor is disconnected.

  • Joseph Weisenberger
    Joseph Weisenberger Jun 22, 2009

    By the way, what is the GEM module?

  • Joseph Weisenberger
    Joseph Weisenberger Jun 22, 2009

    The battery drain was cured by removing the power for the radio, so these two issues were definately related. The expansion tank is remaining full, and the coolant doesn't seem to be overflowing anymore. The level rises slowly after the engine is turned off, just like it would normally act under heat soak conditions. What did you do to get rid of the settled air bubble around your CTS in the 2000 Taurus? The 1996-2001 Model years are all similar, though the technical bulletins may not be the same. Do you know what voltage should be coming from the battery to the terminals of the CTS harness? The more info you can give me, the better I'll be able to troubleshoot this issue. We're taking the car in to Autozone tomorrow to have it hooked up to an OBD-II reader so that I can post the codes. I'm expecting one relating to the CTS since the Check Engine Light came on as soon as we disconnected the CTS. If coolant is wicking up the wires, it would cause a short, correct? Because of this, it would need a new CTS harness pigtail, correct? No need to apologize if you repeat steps already performed, you can't tell what I've done unless I tell you. All the help is greatly appreciated. The sensor is also lower than the upper radiator hose, sitting just to the right of the thermostat housing. I know the thermostat is okay, and the CTS is brand new. Could the teflon tape that is wrapped around the threads be insulating the sensor? There's no tape around the bottom bull-nose that would seem to be the actual sensing mechanism.

  • Joseph Weisenberger
    Joseph Weisenberger Jun 22, 2009

    New cooling system componets: Expansion tank, Radiator Cap, Coolant Temperature Sensor, Lower Radiator Hose, Heator Core by-pass (installed a length of heater hose to loop from the water pump to the hose that contains the CTS and Temperature Sending Unit), Water Pump, Thermostat (tested with a pot of boiling water and digital thermometer- thermostat opens as designed).



    Cooling System Service Performed: Forward and Back flush of Radiator, Chemical flush of cooling system, by-pass of Heater Core, Several drain and fills of coolant complete with bleeding of cooling system (running the engine to allow the coolant to mix with the radiator cap off the bottle- burping each hose after the thermostat opened).

  • Joseph Weisenberger
    Joseph Weisenberger Jun 22, 2009

    Checked voltage at the terminals of the CTS. Both read 12V DC.

  • Joseph Weisenberger
    Joseph Weisenberger Jun 22, 2009

    I may have misread the reading, looking at the analog volt meter. I'll recheck and post the results later today. Would would be other symptoms of a fried PCM?

  • Joseph Weisenberger
    Joseph Weisenberger Jun 22, 2009

    Is there any way to get OE number with out removing PCM?

  • Joseph Weisenberger
    Joseph Weisenberger Jun 23, 2009

    Do you have any other information as to what could be some signs of a bad PCM? I can get another pigtail from Kragen/O'Reiley for around $50.00 once I check the harness again. Can you tell me how to go about checking voltage on the pins? Namely, where do I place the voltage meter, and do I test to an engine ground? How do I know which pin to check? Check the wiring diagram and test the pin that attaches to the wire I'm checking, or do I disconnect the PCM harness and test the pin directly? If it's the wire, I can backprobe it to get a reading.

  • Joseph Weisenberger
    Joseph Weisenberger Jun 24, 2009

    Thanks, I found the calibration code for the PCM on the door panel. Verified it by looking at the PCM wiring harness. Hope to hear back from you on the testing procedure.

  • Joseph Weisenberger
    Joseph Weisenberger Jun 24, 2009

    I could have read the voltage wrong. When I went back to recheck, I wasn't getting any voltage anywhere, so I took my meter into the house, set it to AC, and checked one of the recepticles. No voltage. My meter died somehow, but will read ohms. I'm in the process to getting a new meter to read DC (the one I have at work as a hotel maintenance tech just reads Ohms and AC). As soon as I get the voltage, I'll let you know.

  • Joseph Weisenberger
    Joseph Weisenberger Jun 24, 2009

    The 12 volt reading was taken with the key not even in the ignition. I don't think I had the meter set right.

  • Joseph Weisenberger
    Joseph Weisenberger Jun 24, 2009

    Checked continuity on the wire that sends the signal back to the PCM. Nothing. There has to be a break or a short in this wire, so I'll replace it and let you know how things go.

  • Joseph Weisenberger
    Joseph Weisenberger Jun 25, 2009

    Tested voltage this morning on the terminals. No voltage to either leg with the key in the on position and the PCM connected. I have gotten the new harness ordered through Kragen/O'Reilly, will be picking up Friday afternoon.

  • Joseph Weisenberger
    Joseph Weisenberger Jun 27, 2009

    Replaced the wiring harness/pigtail. Took the car out on a short test run. Parked and thought, "This isn't going to work." Popped the hood, put my hand on the latch to open, and brrrrrrrrrrrrrrrr the fan started right up. This harness shorting out and not operating the cooling fans could have been the root cause to the blown head gasket, cracked timing housing, and cracked head. It feels so good to hear those fans kick on. Thank you so much for all your help, and be assured, you're getting the maxium, four thumbs way up!!!!!!!!! I guess it's not a PCM problem after all! *wipes brow in elation*

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Does the car overheat? I believe disconnecting the coolant temp sensor only turns the fans on as a default precaution to protect the engine. You likely have a wiring issue. The radio and speakers are integrated into the electronic control system as you seem to have figured out. There is also a GEM module under the dash that is also part of the integrated system. Visually check for water entry at the firewall under the dash, and any obvious loose connections or stripped wires. Also, has the car been damaged by a crash? Has it been in a flood? Have aftermarket components been installed and/or removed? I wouldn't condemn the processor yet, but I won't guarantee it hasn't received damage from the original cause. I would get someone to run self test, write them down, clear them, and drive the car. Then, focus on the trouble codes that remain. Pinpoint tests are available in what used to be the Ford 'H' manual. You can find some of these used on ebay for cheap. If you can get the trouble codes, I may be able to point you on a straighter path to finding your problem. Good luck. This kind of problem takes some serious strategy. It is always best to start with a good visual inspection to eliminate the obvious.

Posted on Jun 22, 2009

  • 3 more comments 
  • Eric Amundson Jun 22, 2009

    GEM module controls interior accessories and has a battery saver feature to prevent these from draining the battery. But, like you said, the overheating is the base issue. I think you have separate issues with the tach, radio, and battery drain. I had a 2000 Taurus with a leaking expansion tank. It would leak, the car would warm up and push coolant into the tank, and it would leak again. This caused an air pocket around the coolant temp sensor, fooling it into thinking the car was not as hot. The location of the sensor and the hoses being routed higher than the sensor let the air pocket settle in. If the coolant reservoir/expansion tank stays full, we will keep digging. The cooling fans working when the CTS in unplugged tell me that the PCM is able to detect the fault and command the relay to start the fans. It proves that everything works. There was a technical service bulletin that may or may not have applied to this era about coolant temp sensors leaking just enough coolant to wick up the wires and into the pcm harness. All I can do from here is feed as much info as possible. There's nothing like having the vehicle in front of you. I apologize if I am repeating steps that have already been taken. I hope we can save you some money.

  • Eric Amundson Jun 22, 2009

    If you have 12 volts to both wires while the connector is plugged in, that is too high and one of those wires is shorted to battery power. it is likely to have fried the pcm unless it is the coolant wicking problem. Most vehicles' reference voltage is only 5 to 9 volts. Fix the short before plugging in a new processor.

  • Eric Amundson Jun 22, 2009

    The calibration code in the driver's door jamb should be sufficient if you can find one. It will be a small decal with a number letter combination. Otherwise you may have to pull the processor. What kind of voltage do you have with the cts disconnected? One pin should have vehicle reference voltage of 5 volts. The other should feed a voltage of .4 to 1 volt back to the processor indicating the coolant temp. This is while connected to the sensor because it is relative to the sensor's internal resistance, which varies according to temperature of the coolant. Also, when the key is off, do you have voltage there? This would mean it is a short in the harness. As far as a fried processor, the short would most likely just burn out the coolant temp circuit in the board. It wouldn't necessarily affect the other circuits.

  • Eric Amundson Jun 24, 2009

    Sorry, had a long day. I do not have a wiring diagram, but with the pcm connected, and the cts disconnected, one wire should have around 5 volts with the key on. It sounded like one had 12 volts, which would be a short to power. Put your negative test lead from you voltmeter to a good ground, and the positive to one wire, then the other. There should be close to 5 volts on one, little or nothing on the other. (There could be some slight stray voltage around a volt). Any other readings are cause for concern. Let me know what you get. With the pcm disconnected from the wiring harness, there should be absolutely no voltage on either wire,

  • Eric Amundson Jun 26, 2009

    Sounds like your headed in the right direction. Let's hope the pcm is ok.

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