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Home >> GMC >> 2007 >> Yukon Denali >> Repair and Diagnosis >> External Pages >> Different variant/trim >> Section 2 (Automatic Transmission - 4L60-E/4L65-E/4L70-E - Introduction (2 Of 2)) >> Description and Operation >> Automatic Transmission Hydraulic Diagrams >> Manual Second Gear >> First Gear Prevented

First Gear Prevented

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The prevention of first gear is controlled electronically by the PCM through the 1-2 SS valve. The PCM keeps the 1-2 SS valve de-energized, regardless of the vehicle operating conditions when the TFP manual valve position switch signals manual second gear range. This keeps signal A fluid exhausted and the spring force holds the 1-2 shift valve in the upshift position.