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Old February 17th, 2010, 10:52 AM   #1
cheeperthebetter
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Default TPS or ????

I have 99 GMC 3500 180,000 miles and every time i lift completely off the throttle the torque converter unlocks even if its going down hill and just for a second. I ran the truck with the scan tool plugged in and couldn't find anything wrong there. Transmission fluid looks really clean but I do not know when or who changed the fluid last or if the filter was changed. Local mechanic said it was probably the TPS sensor but I it seemed to be functioning when i was running with the scan tool. Could it still be bad? Or could the filter be clogged? I believe its a 48le transmission.

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Old February 17th, 2010, 11:20 AM   #2
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A dirty or malfunctioning MAF sensor can also cause transmission problems. I think your best bet is to scan the transmission computer, it should tell you why it is unlocking.
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Old February 17th, 2010, 11:31 AM   #3
Flexin' XJ
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What kind of scan tool were you using? The tps voltage changes so rapidly that scan tools cannot see it and then display it quickly enough. You need to graph the data to see if there is a drop off of the voltage. A tech 2 can accomplish this without having to store it and graph it on the computer.

The torque converter unlocks then locks back up when you let off the pedal?
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Old February 17th, 2010, 01:03 PM   #4
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the torque converter unlocks when you let off the gas pedal? every chevy truck i have owned does that.
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Old February 17th, 2010, 02:45 PM   #5
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Yeah, thats totally normal. Its operating exactly as designed to.
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