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Thread: Low Voltage causes Cooling Fan to engage???

  1. #1
    Join Date
    Jun 2017

    Question Low Voltage causes Cooling Fan to engage???

    Hi all,
    My dad's SC is an '89 and he's been trying to track down a voltage drain issue. Pulling out every fuse in the box under the hood and putting them back in one by one, he's pretty much determined the culprit is either the IRCM\CCRM, ( anyone know what the 'real' name of this dang thing is? ), or one of the components downstream that it controls.

    Now here's the weird thing... the last voltage check of the night showed 10.93 volts on the battery... however, sometime during the night, ( as the battery slowly drained ), the fan came on! It was running this morning when he went out to check, and, the battery was down to 3.09 volts ... so the fan had obviously been running and drained it pretty well. Anticipating a couple of questions...

    1. No, the ignition was NOT in the run, ( nor in the on ), position, it was in the OFF position... in fact, the keys are hanging up in the house.
    2. Every fuse had been put back in, there was no drain at all with only the IRCM\CCRM fuse removed. This was the last fuse he put back in, which resulted in a slow, steady battery drain.

    Has anyone ever heard of or experienced this problem?
    Why would the fan remain OFF at 12, 11, 10.x vots... but automagically turn itself on at some lower voltage?

    I'm 'assuming' this is an issue... but if not, then that's one heck of a crummy design on Ford's part... I would think? Unless someone knows of a good reason it would be designed in this way?

    Any help \ thoughts are most appreciated!


  2. #2
    Join Date
    Dec 2007
    Pacific Rim
    Integrated Relay Control Module

    Can you determine which fan circuit was lit that had the fan turning? Low or high?

    Let's start w/wiring diagrams (1st one is for a '93, but the other should be similar to your '89, I think):


    Based on your testing, I think you should find another IRCM, same P/N, at least to test - still no joy, I'd wonder about the EEC health - still no joy, I'd wonder if the wiring on the car has been compromised at some location. Any work done lately? Any welding?
    Last edited by KMT; 06-11-2017 at 06:34 PM.

  3. #3
    Join Date
    Oct 2006
    Valparaiso, Indiana
    Check the passenger side grounding block behind the headlight. My 95 LX had the exact symptoms as you are describing. I replaced the IRCM and still had a drain issue and fan engagement as the battery died. My power antenna would also kick on and run stripping the gear out, 89 won't have that issue since it's a dash switch vs. The automatic one on 94+. As I was diving back in to the area with the IRCM, I found a broken ground going to the block on the core support. I regrounded the wire by itself and the problem went away.

  4. #4
    Join Date
    Nov 2016
    Welcome to the forum! Odd as it may sound if the ignition switch and lower connector are still original very strange things happen.

  5. #5
    Join Date
    Jun 2017
    Hi again all,
    Thanks, everyone, for all the responses!
    The issue(s) now seem to be resolved.

    . Ssssssooooo, it turns out that the IRCM he had in there was incorrect. He obviously needs to have an '89/'90 IRCM, however, the ones that he had been putting back in were out of a '94/'95 and '96 model year car, and, they weren't out of a Super Charged 3.8L either, just a standard 3.8, so that lovely combination caused all sorts of issues such as the weird fan issues, dramatically dropping voltage, and the thing ran incredibly crappy at idle too; it almost refused to start when cold, and wouldn't stay at a decent rpm, it either wanted to be under 600, or, above 1700 rpm at idle. Putting the original '89 IRCM that came out of the car back in fixed the idle problem immediately... go figure huh?
    . The reason for all the confusion there was that we had to tear half the engine bay apart to redo his head gaskets, ( what a royal pain in the butt... I love the older non-computerized cars... so much room in the engine bay and not tons of 'crap' in the way... you can actually work on those without tearing the entire car apart ), but I digress. Anyway, because everything had been disconnected and torn apart, he had thought something happened when putting it back together and was trying to track that down, ( we went through probably 4 different IATs and a few TP sensors as well trying to track that problem down ). That's when he started changing out the IRCMs. He wasn't aware of the incompatibility between the SC and non SC 3.8L cars, not to mention the year differences to boot. Yesterday I looked at the actual pinouts for the '89 and '95 IRCM in the wiring schematics of the service manual... and whaddya know... they ain't the same! '95 non SC is, however, pretty dang close... swap a wire or two in the '89 harness and it would quite 'possibly' work perfectly. There are a few more 'unused' pins on the '89, (they mainly control feeds to the Fuel Pump relay ), so I suspect those would just sit there doing nothing since the '89/'90 uses the EEC to control the Fuel.
    . Anyway... all the issues appear to have been because of this simple mix-up... he's lucky the EEC and\or some other component didn't get fried in the process... so that's a blessing there!

    I've also got another question for folks regarding Ford's wonderful numbering system.
    . For the most part Ford's numbering system is pretty straight forward ...but... he has several IRCM's that definitely came out of either a Thunderbird or a Cougar, ( he took them out, so he knows what they came from... it's not just hear-say ), however, the numbers on them are "F48F-12B577-AB". Now what's confusing is that every single site I've looked at regarding Ford "Engineering" and "Service\Part" numbers says that the third position, ( the "8" in F48F ), is "Capri (US designed parts) 1972-75", Ummmmm, what the heck? There's no way a '90s Thunderbird\Cougar IRCM came out of a '72-'75 anything... what gives with the numbering system here Ford?
    . Anyone have any idea on the "8" and what it actually means in this case\application?

    Thanks once again for everyone's responses... your assistance was greatly appreciated! And thanks for the Diagram, KMT, that's what got me to start looking up the pinouts


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