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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 P0843: Pressure Switch Solenoid "C" Circuit High >> 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 is set in a steady state condition when pressure switch "C" should be in the ON state, but the TCM detects pressure switch "C" in the OFF state for more than 0.1 second. This DTC indicates that an open condition may exist in the vehicle harness, internal transmission harness, or the 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. 1 to ground. Turn ignition on. Does the scan tool indicate pressure switch "C" status as ON? If so, go to next step. If not, go to step  12.
  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 "D" to a known-good ground. Does the scan tool indicate pressure switch "C" status as ON? If so, go to next step. If not, go to step  11.
  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 "A". Does the scan tool indicate pressure switch "C" status as ON? If so, go to next step. If not, go to step  10.
  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 "C" membrane (4). See Figure. Does the scan tool indicate pressure switch "C" status as ON? If so, see DIAGNOSTIC AIDS . If not, go to next step.
  9. Replace the pressure switch manifold. See PRESSURE SWITCH MANIFOLD  under REMOVAL & INSTALLATION. Is the replacement complete? If so, go to step  13.
  10. Replace the internal wiring harness. See TRANSMISSION INTERNAL WIRING HARNESS  under REMOVAL & INSTALLATION. Is the replacement complete? If so, go to step  13.
  11. Repair the vehicle wiring harness. Is the repair complete? If so, go to step  13.
    12. CAUTION: In most cases, the TCM is not at fault. Investigate thoroughly before replacing the TCM.
  12. Replace the TCM. See TRANSMISSION CONTROL MODULE  under REMOVAL & INSTALLATION. Is the replacement complete? If so, go to next step.
  13. 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 "C" operation.

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

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