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Home >> Hummer >> 2006 >> H2 4D Utility Pickup >> Repair and Diagnosis >> Transmission >> Hydraulic Diagrams >> Automatic Transmission - 4L60-E/4L65-E/4L70-E - Removal & Installation, Service, Overhaul, Troubleshooting & Diagnosis >> Description and Operation >> Manual Second Gear >> First Gear Prevented

First Gear Prevented

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.