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Thread: What tells the computer to control the TCC solenoid?

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    Question What tells the computer to control the TCC solenoid?

    I've just rebuilt the 700R4 transmission with new TCC solenoid (Type-6 system) and would like to test the TCC system on the vehicle before I reinstall the trans. It appears by the wiring diagrams I found for my 1987 S10 Blazer 4x4 2.8L w/ auto-trans that the circuit ground would be controlled by the ECM (pin A7) in opening or closing the ground for this circuit.

    I figured out the circuit to test for power from the fusebox to the TCC solenoid connector through the brake (cancel) switch. I've made a simplified diagram from what I saw on larger full-page schematic.

    What I need to know is when the circuit is supposed to be closed and what all other components if any have input to the ECM on this system that would control this circuit so I can test those components as well and confirm overall proper operation. I know the (+) power to the TCC solenoid is supposed to be on with the ignition key, but how and when is the ground controlled?

    According to the larger diagram; The (+) power runs from the fusebox through the brake switch to a harness connector where the wire changes color from Purple to LT Green/Blk, then through a second connector where it changes back to Purple and into the "A" pin on the 700R4 transmission connector. The (-) negative Tan/Blk wire runs back from the "D" pin to the second connector where it splits back to the "A7" pin on the ECM. What makes the ECM open or close this circuit?

    The diagram also shows this Tan/Blk wire continuing back through the second connector changing to Drk Blue to the first connector. It then splits back with a Tan/White wire to the "F" pin at the ALDL. It would seem I should have continuity to ground at this "F" pin only if circuit is closed by the ECM. Does this sound correct? Would this be where to test for overall system operation if/when ground is enabled by checking continuity to another ground source?

    There is also a vacuum line going to the cruise control diaphragm from this brake switch. I know the brake switch plunger knob is supposed to cancel the TCC solenoid operation with pedal movement. What factor does this vacuum hose have in the system? Would this be a "low-vac" switch I've read about for custom hot-rod applications for canceling the solenoid operation when at wide open throttle or low vacuum conditions?

    Click image for larger version. 

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    Re: What tells the computer to control the TCC solenoid?

    Typically this is how it works.

    On a non-ecm controlled vehicle, you need the power going thru a vaccum switch which allows a NC circuit when high vaccum (cruising / light / no throttle) and then thru the brake switch NC which disconnects power if the brake pedal is depressed. Then it goes into the trans harness and on to the TCC solenoid. The ground side of the TCC solenoid will go to a Pressure Switch located on the end of the valve bodys 4th gear circuit. That single terminal PS will provide a ground when the vehicle is in 4th gear.


    There is a couple other ways to do it providing you have an older PCM with a simple circuit, some use both a 3rd and 4th PS inside to allow lockup during 3rd as well and most more modern PCM's have the brake and vaccum inputs already. Thus the latter looks like your diagram. Also some PCMs already have the PS input which would be a 3 or 4 wire plug presence
    2003 S-10 ZQ8 - 262/M5 1986 Pontiac Trans Am - 355/A4

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    Re: What tells the computer to control the TCC solenoid?

    I dont have my ATSG manual in front of me rt now so thats about the best I can do from memory
    2003 S-10 ZQ8 - 262/M5 1986 Pontiac Trans Am - 355/A4

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    Re: What tells the computer to control the TCC solenoid?

    Thanks for the reply, but the internal trans wiring is not really the part of the system I am inquiring about. The #7TAM006B trans in my '87 has the Type-6 system which does not have any internal pressure switches, the two wires go directly to the solenoid.

    I'm wanting to figure out the stock system that powers & controls the circuit and it appears the computer controls when the ground is enabled to close the circuit. So it seems to me after simplifying the circuit from the larger full diagram, that it would be powered at all times with key ON, and grounded by the computer completing the circuit unless cancelled again by either; the computer, brake pedal movement, or by the vacuum line to the same switch unit. Does that sound correct?

    Would the computer depend on the return signals from the manilofld pressure, coolant temp, or any other sensors to determine opening or closing the circuit?

    Source for '87 wiring diagrams.
    http://docs.google.com/leaf?id=0B9SE...zYmQz&cindex=3

    This is from my ATSG book for '87-'93 700R4.
    Click image for larger version. 

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    Last edited by Chzyrider; 09-28-11 at 04:56 AM.

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    Re: What tells the computer to control the TCC solenoid?

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    Attached Thumbnails Attached Thumbnails Click image for larger version. 

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    Last edited by Chzyrider; 09-28-11 at 04:47 AM. Reason: Deleted, double post due to glitch.

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