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Home >> GMC >> 2006 >> Sierra 1500 HD, 4WD >> Repair and Diagnosis >> External Pages >> Different car >> Section 1737 (Automatic Transmission - ALLISON - DTC P0218 To DTC P0878) >> DTC P0877 or P0878 >> Circuit/System Testing

Circuit/System Testing

WARNING: This page is about a different car, the 2010 GMC Sierra, 2010 GMC Cab & Chassis Sierra, 2010 Chevrolet Silverado, and 2010 Chevrolet Cab & Chassis Silverado. However, it is still accessible from the selected car via links, so may be relevant.
  1. Ignition OFF, disconnect the X175 harness connector at the transmission.
  2. Ignition ON, engine OFF, verify with a scan tool the TFP Switch 4 parameter is High.
    • If not the specified value, test the PS4 signal circuit for a short to ground. If circuit tests normal, replace the TCM.
  3. Ignition ON, connect a 3A fused jumper wire to the PS4 signal circuit terminal K to ground. Verify with a scan tool the TFP Switch 4 parameter changes from High to Low when the signal circuit is grounded.
    • If not the specified value, test the PS4 signal circuit for an open/high resistance. If the circuit tests normal, replace the TCM.
  4. Ignition OFF, connect the X175 harness connector to the transmission.
  5. Remove the pressure switch module from the valve body. Leave the internal wire harness connected to the pressure switch manifold. Refer to Pressure Switch Manifold Replacement .
  6. Connect a jumper wire to the base of the pressure switch module and ground.
  7. Ignition ON, engine OFF, gently push on the PS4 with the eraser end of a pencil. Verify with a scan tool that the TFP Switch 4 parameter changes from Low to High when the PS4 is depressed.
    • If not the specified value, test the internal wire harness PS4 signal circuit for an open/high resistance or short to ground. If the circuit tests normal, replace the pressure switch manifold.
  8. Remove the control valve body. Refer to Control Valve Body Replacement .
  9. Disassemble the control valve body assembly and carefully inspect the separator plate for a blocked orifice. Repair or replace as necessary. Refer to Control Valve Body Assembly Disassemble .
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