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Thread: 2000 2500 Truck 4L80E - Doesn't respond to the brake switch?

  1. 01-26-2009 #1
    terryk
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    Question 2000 2500 Truck 4L80E - Doesn't respond to the brake switch?

    I searched here and other places and found only one reference here. My question is:

    Is the brake switch ignored on the 4L80E TCC used in the 2500 trucks (MY2000 with a 6.0L specifically)?

    If I press my brake pedal the TCC doesn't unlock. I checked the switch and wires to the EBCM and they are fine. The VCM scanner doesn't show a status toggle for the Brake Switch but it does show it for the Cruise Brake switch. Since the same input wire to the EBCM is used for both the TCC and Cruise disengage when the brake pedal is pressed, I have to assume the EBCM is getting the signal (and the fact that pressing the brake disengages the Cruise). The trans shifts fine.

    Since the TCC unlocks on a throttle release you would never know it. Driveability-wise it's fine. On the scanner, TCC looks great. It locks and unlocks nicely and has low slip, seems to follow the specs dead on.

    I did find a couple of people that noticed the same thing with their 99+ trucks with the 4L80E. Pressing the brake pedal does squat. They don't have any issues either, they just noticed it doesn't do anything.

    Has anyone here noticed the same thing? Is it possible you can change the calibrations to ignore the switch? I haven't checked for a modified calibration (just bought the truck) but I thought that might be a stretch.

    Any thoughts or experience would be appreciated.

    Terry
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  2. 01-26-2009 #2
    Frost
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    I'd love to find the cal that keeps it locked when throttle is release UNTIL speed is low enough or the brake pedal is touched but I have not had the luck. If others have, they aren't sharing it either it seems...
    Steve Williams
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  3. 01-26-2009 #3
    terryk
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    I'm from the pre-OBDII days but isn't there a minimum TCC lock speed? Two values with a hysteresis window? Or is that sooooo yesterday.
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  4. 01-26-2009 #4
    Russ K
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    The brake switch doesn't unlock the TCC on the 4L80E trans.

    Russ Kemp
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  5. 01-26-2009 #5
    terryk
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    Smile

    Quote Originally Posted by Russ K View Post
    The brake switch doesn't unlock the TCC on the 4L80E trans.

    Russ Kemp
    Well I wish they would put that in the service manual in BOLD ITALICS UNDERLINED GIANT PURPLE TEXT!!!!

    After reading more, they don't explicitly say that but it's implied that it doesn't.

    Thanks!
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