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Home >> GMC >> 1998 >> Yukon RWD >> Repair and Diagnosis >> External Pages >> Different car >> Section 70 (Automatic Transmission Diagnosis - 4L80-E (Gasoline)) >> Diagnostic Tests >> DTC P0756: 2-3 Shift Solenoid ("B") Performance Malfunction >> Diagnostic Procedures

Diagnostic Procedures

WARNING: This page does not describe the selected car, but rather 14 other vehicles, including the 1998 GMC Savana Special, 1998 GMC Savana Camper Special, 1998 GMC Savana, 1998 Chevrolet RV Cutaway, and 1998 Chevrolet Cutaway. However, it is still accessible from the selected car via links, so may be relevant.
  1. Connect scan tool to DLC. Turn ignition switch to ON position. DO NOT start engine. Using scan tool, record freeze frame and failure records for reference. Data will be lost when DTCs are cleared later in this test.
  2. Start engine and let idle. Apply parking brake. While observing scan tool, shift transmission into each gear position. If gear position matches Transmission Fluid Pressure (TFP) position switch A/B/C display on scan tool, go to next step. If gear position does not match Transmission Fluid Pressure (TFP) position switch A/B/C display on scan tool, diagnose TFP position switch. Switch is also referred to as Pressure Switch Assembly (PSA). See COMPONENT TESTS . Also see DTC 1810.
  3. Raise and support vehicle. Start engine. Shift gear selector into "D4" position. Using scan tool, command 1st, 2nd, 3rd and 4th gears while accelerating vehicle. If 1st gear was commanded but not achieved or gear other than 4th gear occurred in 4th gear, check shift solenoids for damaged seals or internal malfunction. Repair shift solenoids as necessary, then go to next step. If all gears commanded were achieved, see DIAGNOSTIC AIDS.
  4. After repair is complete, select DTC on scan tool. Select "Clear Info" function. Test drive vehicle. Hold throttle at 25 percent and accelerate vehicle to 50 MPH. Ensure VCM detects correct ratio for each commanded gear for more than one second in "D1", "D2", "D3" and "D4". In "D4", wait for lock-up to occur. Select "Specific DTC" and enter DTC "P0756". If DTC P0756 is not present, repair is complete. If DTC P0756 is still present, repeat test.
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