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  • #1

    Fans not working...can't figure out why

    About two weeks ago, I started the car up, and let it run for about 15 minutes. (I do this once a week as I don't use it in the winter). Anyway, I came out an noticed the temp was near 240 degrees! I quickly popped the hood and turned on the defroster to cool it off. The temps quickly dropped (thank goodness the unheated garage was in the low 20's that day), but I did not hear the fans come on. Usually, the defroster turns the fans on, since the compressor is activated.

    Anyway, after much searching, I discovered the fuse for the fans blew. I replaced the fuse, and thinking everything was fine, tried again. The temp rose again, but no fans.

    Here's what I''ve checked so far:
    All three relays are fine. Checked them in the fog light circuit...all checked out.
    The fuse has not blown again, and I'm seeing 12vdc across the fuse.
    The engine temp sensors are both working. I scanned the computer in real-time and verified both the gauge sensor and the PCM sensor were reading the temperature accurately.

    What I haven't done is verified that the fans are both getting power. Since I need to jack up the car to do this, I'm . Because of the fan shrouds, it's difficult to see if they are running at all (even slow speed). Because there are two fans, I don't think both failing at the same time is likely, but I'm not positive. Never heard of this happening...

    Anyway, is it possible the computer is not sending the signal to turn the fans on? Wouldn't a trouble code be set?

    How can I continue to diagnose the problem?
    Al 96 Ram Air T/A
    Mods: Build # 784 * Hotchkis STB * SFCs * Borla cat back w/QTP cut-out * AS&M/RK Sports Mid-length headers w/single CAT * Koni SA shocks on lower perch w/ lowered rear * Strano Hollow front & rear antisway bars * 1LE front/rear springs * 1LE aluminum driveshaft * Strange 4.10 gears w/ Zexel Torsen diff. * ARP bearing cap studs & aluminum diff cover* J&M Hotpart poly/poly rear LCAs and poly/poly panhard bar * RAM Powergrip clutch w/ LT4 PP and RAM billet Al flywheel * C5 Z06 brakes * C6 Z06 wheels * Spohn T/A * Spohn DS Loop * fully custom interior w/ custom audio
    Tags: None
  • #2
    Using tests I found on shbox.com, I did the following:

    I know the fans work. I applied 12vdc to each and they spun. I then jumped relay #1 and the fans turned on.

    I tried putting the car into field service mode (jumping pins #5 and #6 under the dash) but the fans did not turn on.

    I tested the lead from the PCM which should show 5vdc, but no luck.

    I'm thinking the computer is not sending the signal to close the relays.

    This all started when the battery died and I charged it up. Do you think the PCM is the issue? If so, why would it not show any other issues? Everything runs fine, just no fans...

    I even tried resetting the PCM by disconnecting the battery for a bit.
    Al 96 Ram Air T/A
    Mods: Build # 784 * Hotchkis STB * SFCs * Borla cat back w/QTP cut-out * AS&M/RK Sports Mid-length headers w/single CAT * Koni SA shocks on lower perch w/ lowered rear * Strano Hollow front & rear antisway bars * 1LE front/rear springs * 1LE aluminum driveshaft * Strange 4.10 gears w/ Zexel Torsen diff. * ARP bearing cap studs & aluminum diff cover* J&M Hotpart poly/poly rear LCAs and poly/poly panhard bar * RAM Powergrip clutch w/ LT4 PP and RAM billet Al flywheel * C5 Z06 brakes * C6 Z06 wheels * Spohn T/A * Spohn DS Loop * fully custom interior w/ custom audio

    Comment

    • #3
      Spent another few hours...

      It seems all things are pointing back to the computer. The 5vdc reference signal from the PCM to turn on the fans is not being sent. Is there anything else that would cause this?

      Is the PCM shot? Can they be repaired or do I need to order a new one???
      Al 96 Ram Air T/A
      Mods: Build # 784 * Hotchkis STB * SFCs * Borla cat back w/QTP cut-out * AS&M/RK Sports Mid-length headers w/single CAT * Koni SA shocks on lower perch w/ lowered rear * Strano Hollow front & rear antisway bars * 1LE front/rear springs * 1LE aluminum driveshaft * Strange 4.10 gears w/ Zexel Torsen diff. * ARP bearing cap studs & aluminum diff cover* J&M Hotpart poly/poly rear LCAs and poly/poly panhard bar * RAM Powergrip clutch w/ LT4 PP and RAM billet Al flywheel * C5 Z06 brakes * C6 Z06 wheels * Spohn T/A * Spohn DS Loop * fully custom interior w/ custom audio

      Comment

      • #4
        Did you check the fusible link for the fans? See Shoebox's wiring diagrams.

        The PCM supplies a ground to the control circuit, to turn on the fans. It does not supply +5V.

        At the point where you tested for the signal from the PCM, did you verify the coolant temp reading in the PCM was at 226*F or above for the low speed relay and 235*F or above for the high speed relay?

        The PCM should be checking the control circuit voltages for the relays, and setting codes if the voltage (0V or 12V) does not match the operating state ("on" of "off").
        Fred

        381ci all-forged stroker - 10.8:1 - CNC LT4 heads/intake - CC solid roller - MoTeC engine management - 8 LS1 coils - 58mm TB - 78# injectors - 300-shot dry nitrous - TH400 - Gear Vendor O/D - Strange 12-bolt - 4.11's - AS&M headers - duals - Corbeau seat - AutoMeter gauges - roll bar - Spohn suspension - QA1 shocks - a few other odds 'n ends. 800HP/800lb-ft at the flywheel, on a 300-shot. 11.5 @ 117MPH straight motor

        Comment

        • #5
          Well, the trigger issue could be a good thing, as I thought, like most relays, it was supplying voltage to close the relay. But, if it is supposed to ground the system, then your right, I wouldn't see anything. I am seeing 5vdc on the other side, which means the computer is working.

          As for the coolant sensor, yes, I used a scanner to see if the PCM was seeing the right temps. I'm assuming if the PCM can "speak" to the sensor, then the sensor is working.

          The fusible link I assumed was fine. Using both Shoebox's diagrams and my Helm's manuals, I checked relay #1, D1, and saw 12vdc. If the link broke, then I wouldn't think I would see anything at D1.right?

          The manual says the link is located "above RH shock tower, in battery junction box."

          Dumb question, but where is this? RH is the driver's side right?

          Electrical problems drive me crazy
          Al 96 Ram Air T/A
          Mods: Build # 784 * Hotchkis STB * SFCs * Borla cat back w/QTP cut-out * AS&M/RK Sports Mid-length headers w/single CAT * Koni SA shocks on lower perch w/ lowered rear * Strano Hollow front & rear antisway bars * 1LE front/rear springs * 1LE aluminum driveshaft * Strange 4.10 gears w/ Zexel Torsen diff. * ARP bearing cap studs & aluminum diff cover* J&M Hotpart poly/poly rear LCAs and poly/poly panhard bar * RAM Powergrip clutch w/ LT4 PP and RAM billet Al flywheel * C5 Z06 brakes * C6 Z06 wheels * Spohn T/A * Spohn DS Loop * fully custom interior w/ custom audio

          Comment

          • #6
            The fusable link in the battery junction box is the main link from the battery. There is an individual link on the fan.
            Tracy, 97 Formula, pretty much stock.

            Comment

            • #7
              I found the links. Now to figure out which one does what...
              Al 96 Ram Air T/A
              Mods: Build # 784 * Hotchkis STB * SFCs * Borla cat back w/QTP cut-out * AS&M/RK Sports Mid-length headers w/single CAT * Koni SA shocks on lower perch w/ lowered rear * Strano Hollow front & rear antisway bars * 1LE front/rear springs * 1LE aluminum driveshaft * Strange 4.10 gears w/ Zexel Torsen diff. * ARP bearing cap studs & aluminum diff cover* J&M Hotpart poly/poly rear LCAs and poly/poly panhard bar * RAM Powergrip clutch w/ LT4 PP and RAM billet Al flywheel * C5 Z06 brakes * C6 Z06 wheels * Spohn T/A * Spohn DS Loop * fully custom interior w/ custom audio

              Comment

              • #8
                I assume you are aware that Rob/Shoebox has the wiring diagrams for the fans. Not sure, be he may also have a "how to" for checking fusible links.

                http://shbox.com/1/1995_pcm6.jpg
                Fred

                381ci all-forged stroker - 10.8:1 - CNC LT4 heads/intake - CC solid roller - MoTeC engine management - 8 LS1 coils - 58mm TB - 78# injectors - 300-shot dry nitrous - TH400 - Gear Vendor O/D - Strange 12-bolt - 4.11's - AS&M headers - duals - Corbeau seat - AutoMeter gauges - roll bar - Spohn suspension - QA1 shocks - a few other odds 'n ends. 800HP/800lb-ft at the flywheel, on a 300-shot. 11.5 @ 117MPH straight motor

                Comment

                • #9
                  Yup...will be going out to work on the links after lunch (too cold out there now).

                  Thanks for the help...
                  Al 96 Ram Air T/A
                  Mods: Build # 784 * Hotchkis STB * SFCs * Borla cat back w/QTP cut-out * AS&M/RK Sports Mid-length headers w/single CAT * Koni SA shocks on lower perch w/ lowered rear * Strano Hollow front & rear antisway bars * 1LE front/rear springs * 1LE aluminum driveshaft * Strange 4.10 gears w/ Zexel Torsen diff. * ARP bearing cap studs & aluminum diff cover* J&M Hotpart poly/poly rear LCAs and poly/poly panhard bar * RAM Powergrip clutch w/ LT4 PP and RAM billet Al flywheel * C5 Z06 brakes * C6 Z06 wheels * Spohn T/A * Spohn DS Loop * fully custom interior w/ custom audio

                  Comment

                  • #10
                    Not sure what I did, but the problem is resolved. After checking every single wire and circuit, I was about to give up. I started her up, let the temperature rise, but this time, when it hit 224, I noticed it started to drop. Once it hit about 210, it rose again. It did this several times, telling me the low speed fans were working again. I revved it up to get her good and hot, and at about 230, the high speed fans kicked in.

                    Wish I knew what I did, but it works again. I'm wondering if leaving the battery disconnected for an hour reset the PCM.

                    Oh well, on with the game.

                    Thank you to all that offered suggestions. It's nice to be able to bounce ideas of you guys.
                    Al 96 Ram Air T/A
                    Mods: Build # 784 * Hotchkis STB * SFCs * Borla cat back w/QTP cut-out * AS&M/RK Sports Mid-length headers w/single CAT * Koni SA shocks on lower perch w/ lowered rear * Strano Hollow front & rear antisway bars * 1LE front/rear springs * 1LE aluminum driveshaft * Strange 4.10 gears w/ Zexel Torsen diff. * ARP bearing cap studs & aluminum diff cover* J&M Hotpart poly/poly rear LCAs and poly/poly panhard bar * RAM Powergrip clutch w/ LT4 PP and RAM billet Al flywheel * C5 Z06 brakes * C6 Z06 wheels * Spohn T/A * Spohn DS Loop * fully custom interior w/ custom audio

                    Comment

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