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Home >> GMC >> 2003 >> Safari Van Cargo, AWD >> Repair and Diagnosis >> External Pages >> Different car >> Section 72 (Automatic Transmission Diagnosis - 4L80-E (Diesel)) >> Diagnostic Tests >> DTC P0751: 1-2 Shift Solenoid Valve - Performance >> Diagnostic Procedure

Diagnostic Procedure

WARNING: This page is about a different car, the 2002 GMC Cab & Chassis Sierra and 2002 Chevrolet Cab & Chassis Silverado. However, it is still accessible from the selected car via links, so may be relevant.
  1. Did you perform the diagnostic system check? If so, go to next step. If not, see DIAGNOSTIC SYSTEM CHECK  under SELF-DIAGNOSTIC SYSTEM.
  2. Install a scan tool. Turn ignition on, engine off. Before clearing the DTCs, use the scan tool to record the freeze frame and failure records. Using the CLEAR INFO function erases the freeze frame and failure records from the PCM. Record the freeze frame and failure records. Clear the DTCs. Select TFP SWITCH A/B/C on the scan tool. With the engine operating, apply the brake pedal, and select each transmission range. Does each selected transmission range match the scan tool TFP switch display? See TFP MANUAL VALVE POSITION SWITCH LOGIC  table under DESCRIPTION & OPERATION. If so, go to next step. If not, see DTC P1810: TFP MANUAL VALVE POSITION SWITCH ASSEMBLY - CIRCUIT MALFUNCTION  .
  3. Raise and support the drive axle assembly. Start the engine. Place gearshift lever in the "D4" position, use the scan tool to command 1st, 2nd 3rd and 4th gears while accelerating the vehicle. Was a 2-2-3-3 or 1-1-4-4 shift pattern only detected? If so, go to next step. If not, see DIAGNOSTIC AIDS  .
  4. Inspect the shift solenoid/hydraulic circuit for a 1-2 shift solenoid valve internal malfunction. Inspect the shift solenoid/hydraulic circuits for a stuck 1-2 or 3-4 shift valve. Inspect the shift solenoid/hydraulic circuit for damaged seals on one or both of the shift solenoids. See SYMPTOM DIAGNOSIS  under TROUBLE SHOOTING. Did you find and correct the condition? If so, go to next step. If not, see DIAGNOSTIC AIDS  .
  5. Perform the following procedure to verify the repair:
    • Select DTC.
    • Select CLEAR INFO.
    • Operate the vehicle.
    • Place the gearshift lever in the "D4" position.
    • Hold the throttle greater than 10 percent, and accelerate to 55 MPH.
    • The PCM must see the proper gear ratio for each commanded gear for greater than one second in 1st, 2nd, 3rd, and 4th with TCC locked.
    • Select SPECIFIC DTC.
    • Enter DTC P0751.

    Has the test run and passed? If so, system is okay. If not, go to step  1 .

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