ATSG CONFIRMED FIX
Confirmed fix - 6L80E- 2014 GMC Sierra 1500
Complaint: After overhaul truck has no forward movement in any shifter position, reverse is fine.
Cause: 1-2-3-4 shuttle valve was stuck in its bore, not allowing 1-2-3-4 regulator valve to move.
Correction: Either replace the valve body or clean up valve body bore and valve if possible.
Part numbers related to the repair: OE part number very by years, use vin number for correct part numbers.
Year Make and Model of the Vehicle: 2014 GMC Sierra 1500 4wd 5.3L
Mileage: N/A
Shop Name: 3J's Transmission
Transmission: 6L80E
Additional Notes: Vehicle came in for overhaul due to converter clutch failure that had contaminated the internal of unit, when it came in it did have forward movement.
After the overhaul it had no forward movement in any shifter position, reverse was fine. When putting it in forward you could not feel in engagement, and when looking at input data on a scan tool, you could not see the input speed sensor stop or see the pressure switch change for the 1-2-3-4 clutch. This is the only hydraulic element needed for 1st gear take off, the low sprag is the holding element.
Clutch Pressure Control solenoid #5 is used to control fluid flow to the 1-2-3-4 regulator valve and boost valve. When the solenoid is commanded on by the TCM it will control the amount of exhaust fluid out of the solenoid to maintain a specific control pressure, this allows the 1-2-3-4 regulator position for apply and release of the 1-2-3-4 clutch.
Since the shuttle valve was stuck in the bore, the 1-2-3-4 regulating valve could not move, this blocked the flow of hydraulic pressure to the 1-2-3-4 clutch not allowing it to apply, result would be no forward movement in any position.
Tech called back to confirm the fix.
Pictures: Included below, valve #342 is the shuttle valve that was stuck.
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