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Home >> Chevrolet >> 2002 >> Blazer 4D Utility, 4WD, Part Time >> Repair and Diagnosis >> External Pages >> Different car >> Section 82 (Automatic Transmission Diagnosis - ALLISON) >> Diagnostic Tests >> DTC P0846: Pressure Switch Solenoid "D" Circuit Stuck Open >> Diagnostic Procedure

Diagnostic Procedure

WARNING: This page is about a different car, the 2002 GMC Sierra, 2002 GMC Cab & Chassis Sierra, 2002 Chevrolet Silverado, 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. Check the transmission fluid level. See appropriate AUTOMATIC article in TRANSMISSION SERVICING. Is the transmission fluid level correct? If so, go to next step. If not, see appropriate AUTOMATIC article in TRANSMISSION SERVICING.
  3. Measure the line pressure. See HYDRAULIC PRESSURE TESTS  under PERFORMANCE TESTS. Is the pressure within the specified value? If so, go to next step. If not, see SYMPTOM DIAGNOSIS  under TROUBLE SHOOTING.
  4. This DTC indicates that when solenoid "D" was commanded on, pressure switch "D" status remained in the OFF position for more than 2-4 seconds (depending on fluid temperature). This DTC may indicate a stuck shift valve, a mechanically failed solenoid, or a defective pressure switch manifold. Go to next step.
  5. Turn ignition off. Disconnect the TCM C2 connector from the TCM, and install Breakout Box (J-39700) and Breakout Box Adapter (J-43799). Connect TCM connector C2 terminal No. 2 to ground. Turn ignition on. Does the scan tool indicate pressure switch "D" status as ON? If so, go to next step. If not, go to step  15.
  6. Turn ignition off and reconnect the TCM C2 connector to the TCM. Disconnect the transmission in-line 20-way connector. Turn ignition on. Connect a wire from engine side of transmission in-line 20-way connector terminal "F" to a known-good ground. Does the scan tool indicate pressure switch "D" status as ON? If so, go to next step. If not, go to step  14.
  7. Remove the oil pan. See appropriate AUTOMATIC article in TRANSMISSION SERVICING. Disconnect the internal wiring harness from the pressure switch manifold, and ground pressure switch manifold connector terminal "B". Does the scan tool indicate pressure switch "D" status as ON? If so, go next step. If not, go to step  13.
  8. Remove the pressure switch manifold from the control valve body and leave the internal harness connected. Provide a ground connection for the pressure switch manifold to either the control valve body or the transmission main case. Use your finger to push gently on the pressure switch "D" membrane (3). See Figure. Does the scan tool indicate pressure switch "D" status as ON? If so, go to next step. If not, go to step  12.
  9. Remove the control valve body, and check for a stuck or sticking shift valve "D". See appropriate AUTOMATIC article in TRANSMISSION SERVICING. Was the shift valve "D" stuck or sticking? If so, go to step  11. If not, go to next step.
  10. Replace the shift solenoid "D" and reinstall the control valve body. Is replacement of solenoid and reinstalling of valve body complete? If so, go to step  16.
  11. Clean and/or polish the sticking valve to restore free movement or replace the control valve body assembly. Was free movement restored or valve body replaced? If so, go to step  16.
  12. Replace the pressure switch manifold. See PRESSURE SWITCH MANIFOLD  under REMOVAL & INSTALLATION. Is the replacement complete? If so, go to step  16.
  13. Replace the internal wiring harness. See TRANSMISSION INTERNAL WIRING HARNESS  under REMOVAL & INSTALLATION. Is the replacement complete? If so, go to step  16.
  14. Repair the vehicle wiring harness. Is the repair complete? If so, go to step  16.
    15. CAUTION: In most cases, the TCM is not at fault. Investigate thoroughly before replacing the TCM.
  15. Replace the TCM. See TRANSMISSION CONTROL MODULE  under REMOVAL & INSTALLATION. Is the replacement complete? If so, go to next step.
  16. Perform the following procedure to verify the repair:
    • Clear the DTC.
    • Operate the vehicle under normal driving conditions.
    • Using the scan tool, monitor pressure switch "D" operation.

    Did the DTC return? If so, go to step  1. If not, system is okay.

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