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Home >> GMC >> 2006 >> Sierra 1500 HD, RWD >> Repair and Diagnosis >> External Pages >> Different car >> Section 1373 (Automatic Transmission - ALLISON - DTC P0218 To DTC P0878) >> DTC P0721 or P0722 >> Circuit/System Testing

Circuit/System Testing

WARNING: This page is about a different car, the 2009 GMC Sierra, 2009 GMC Cab & Chassis Sierra, 2009 Chevrolet Silverado, and 2009 Chevrolet Cab & Chassis Silverado. However, it is still accessible from the selected car via links, so may be relevant.
    NOTE: You must perform the Circuit/System Verification first.
  1. Ignition OFF, remove the vehicle speed sensor connector.
  2. Connect the J 38522:  generator to the vehicle speed sensor circuit, terminals A and B.
  3. Adjust the J 38522:  generator to 30 V, frequency to 1K Hz, and duty cycle to 50 percent.
  4. Ignition ON, engine OFF, use a scan tool to verify the Transmission OSS parameter is between 1450 to 1550 RPM.
    • If not the expected value, check the vehicle speed signal and ground circuits for an open/high resistance, short to ground, or a short to voltage. If circuits test normal, replace the TCM. Refer to Control Module References for TCM replacement, setup, and programming.
  5. Test or replace the vehicle speed sensor. Refer to Speed Sensor Replacement for 2WD models or Vehicle Speed Sensor Replacement for 4WD models.
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