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  1. #1

    Default I've got trouble - Transmission?

    VERY strange issue today (2000 GMC Sierra 4x4)

    I backed out of the driveway and all was good.

    I put it into Drive and at that point my tack, speedometer, and the gear indicator lights on the dash all died.

    I turned the truck off then on again and they came back. However as I started driving I found that the engine would rev but I would not get the same corresponding moving power. It was like a slipping clutch on a standard (this is automatic). I thought oh no..transmission is shot. I had to get to town and I live a few miles out. The acceleration was not right. On the highway my rpms were higher than they ought to be. I shifted from overdrive to 3rd but the truck did not change. So I assumed I was not on O/D.

    When I got to town I tried a couple things. I found that if I shifted into 2nd I would immediately lose my tach/speedometer and indicator lights again. Turn truck off / on and they come back.

    Does anyone have any thoughts on whether this is related? I just got the truck...prev owner never mentioned any issues. I drove it a bunch and the tranny had seemed very smooth.

    It is scheduled to go into the shop tonight for ball joints and a couple other things. I'd like to give the wrench some ideas as he is an independant and may not be familiar with the truck.

  2. #2

    Default

    So I have been googling like crazy. Found other GM Truck owners talk about a similar situation. They say they lose 1st gear and OD .. which could be what happened to me. I know 1st was "off" and there was no OD.

    They all seemed to say they needed a new Ignition Switch? Not sure how that is related...

    thoughts?

  3. #3

    Default

    Yes indeed. The ignition switch causes a voltage drop at the transmission solenoids which causes the transmission to go into failsafe mode. The dimming dash lights and tach problems are another indication of a bad switch. You will have transmission trouble codes but the reason is the switch.
    Jim

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  4. #4

    Default

    Quote Originally Posted by Jimmiee View Post
    Yes indeed. The ignition switch causes a voltage drop at the transmission solenoids which causes the transmission to go into failsafe mode. The dimming dash lights and tach problems are another indication of a bad switch. You will have transmission trouble codes but the reason is the switch.

    Thanks for the info!!

  5. #5
    Sr. Apprentice brianj's Avatar
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    Default

    Just had the same issues with my '95.It set codes for the 3-4 shift solenoids (4l80E trans) and locked the trans into failsafe. Yep- ignition switch.

  6. #6

    Default

    Mechanic said the wiring harness was clearly shot and is ordering a new one. Hopefully (and I would assume) this was the only issue...and there isn't also some solonoid crap goin on...

  7. #7

    Default

    Good deal. Keep us posted when you get it fixed.

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