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  • #1

    Wiring Question

    94 Firebird 3.4 V6
    The relay ground (female #2) for the coolant fan has a high resistance to ground reading.

    This causes the fan to be inoperative even though the connector to the coolant temp sender is jumpered. Because of this, the scan tool gives a reading of 304 degrees F. That ought to make the PCM want to turn the fan on.

    I don't have a wiring diagram for the under hood fuse box and its relays.

    What color wire is the ground and where does it ground at?
    Tags: None
  • #2
    Ok, it's a green 16 or 18 gauge wire. Does this go through the firewall connector? If so, where does it ground? Does it end up at connector B2 on the Powertrain Control Module?

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    • #3
      My Chiltons shows the "coolant fan relay control" ground wire as a dark green wire to pin B2. In the V8's the fan wires run through body connector C100. Not sure about the V6.
      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

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      • #4
        Yeah, I have Chilton's too. Wiring diagrams are lame.

        Anyone have a service manual or AllData access?

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        • #5
          B2 and relay plug #2 = 0 ohms.

          What does the PCM need to see to ground B2?

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          • #6
            Grounding B2 switches the fan on.

            When the jumper is removed from the coolant temp sensor connector, according to the scan tool, the temp drops from 304F to -38F. So the PCM should be seeing the same data.

            What next?

            Also, if it is the PCM, can one w/ the same service # be purchased via Ebay & installed or does it have to be programmed for the VIN.

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            • #7
              Just for drill if you turn on A/C and have refrigerant pressure that is greater than 20 PSI the fans should run (PCM should pull B2 to ground). If not. it looks like the fan relay driver in the PCM is shot which is a pretty rare condition. In answer to your question if you can find a '94 PCM from a 3.4 , with the same tranny, rear then it should work w/o requiring a tune. Just your PCM vin number will not match the car's, no big thing since it's not scanned for emissions. If you just go by part number off the rack that matches the tranny (AT or MT) then it may need to be tuned as you don't know the donor car model or setup.. Here is a source that programs them for you and gives a 1 yr , but the cost is higher than a junk yard unit. http://stores.ebay.com/SpareECM
              I'm Bob... 1994 Z28 A4, K&N CAI, 160 T-stat, LT4 Hot Cam, 1.6 RR, Pacesetter LT's, Corsa CatBack, Transmission Perform Switch, 3.42 rear, TunerCat $EE, FreeScan & TTS DataMaster-EE.

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              • #8
                Put every thing back together.

                Fan comes on at 228F, cools engine down to 208F, PCM kills the ground to the fan relay, fan switches off.

                Works as designed.

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