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Home >> GMC >> 2006 >> Sierra 1500 HD, RWD >> Repair and Diagnosis >> External Pages >> Different car >> Section 1048 (Automatic Transmission - 6L50/6L80/6L90 - DTC P0218 To DTC P0971) >> DTC P0776 or P0777 >> Circuit/System Verification

Circuit/System Verification

WARNING: This page is about a different car, the 2008 GMC Sierra, 2008 GMC Cab & Chassis Sierra, 2008 Chevrolet Silverado, and 2008 Chevrolet Cab & Chassis Silverado. However, it is still accessible from the selected car via links, so may be relevant.
  1. Perform the Transmission Fluid Check . The fluid must be full and in good condition.
  2. Start engine in park and wait a moment. Shift to Reverse, pause, and then shift to Drive (D6) without allowing the vehicle to move.
  3. View scan tool parameters Commanded Gear and Gear Ratio.
  4. Operate the vehicle in drive from a complete stop, with the calculated throttle position greater than 15 percent to obtain 56 km/h (35 mph) or more.
  5. Make certain 3rd, 5th and Reverse gears are attainable. Use the two scan tool parameters and refer to the Shift Solenoid Valve State and Gear Ratio table to verify the correct ratio for the commanded gear.
    • If the DTC resets, go to Circuit/System Testing.
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