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Home >> Chevrolet >> 2002 >> Blazer 4D Utility, 4WD, Part Time >> Repair and Diagnosis >> External Pages >> Different car >> Section 70 (Automatic Transmission Diagnosis - 4L80-E (Gasoline)) >> Diagnostic Tests >> DTC P0748: Pc Solenoid Circuit - Electrical Malfunction >> 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 failure records. Using the CLEAR INFO function erases the failure records from the PCM. Record the failure records. Clear the DTCs. With the transmission in Park, start the engine. Using the transmission output control function on the scan tool, apply 0.1-1.0 amps while observing the PC REF. CURRENT and the PC ACT. CURRENT. Is the PC ACT. CURRENT reading always within 0.16 amp of the PC REF. CURRENT? If so, see DIAGNOSTIC AIDS  . If not, go to next step.
  3. Turn ignition off. Disconnect the transmission in-line 20-way harness connector. Additional DTCs will set. Install the Jumper Harness (J-44152) on the transmission side of the 20-way connector. Using a DVOM and the Connector Test Adapter Kit (J-35616-A), measure the resistance between terminals "C" and "D". Does the resistance measure 3-7 ohms? If so, go to step  7 . If not, go to next step.
  4. Is the resistance greater than 7 ohms? If so, go to next step. If not, go to step  6 .
  5. Test the PC solenoid valve high (1228) and low (1229) control circuits for an open between the transmission in-line 20-way connector and the PC solenoid valve. Did you find the condition? If so, go to step  15 . If not, go to step  14 .
  6. Test the PC solenoid valve high (1228) and low (1229) control circuits for a short together between the transmission in-line 20-way connector and the PC solenoid valve. Did you find the condition? If so, go to step  15 . If not, go to step  14 .
  7. Test the PC solenoid valve high control circuit (1228) for a short to the transmission case between the transmission in-line 20-way connector and the PC solenoid valve. Test the PC solenoid valve high control circuit (1228) for a short to other power and ground circuits in the transmission harness. Test from terminal "C" to all other terminals in the transmission in-line 20-way connector. Did you find the condition? If so, go to step  15 . If not, go to next step.
  8. Test the PC solenoid valve low control circuit (1229) for a short to the transmission case between the transmission in-line 20-way connector and the PC solenoid valve. Test the PC solenoid valve low control circuit (1229) for a short to other power and ground circuits in the transmission harness. Test from terminal "D" to all other terminals in the transmission in-line 20-way connector. Did you find the condition? If so, go to step  15 . If not, go to next step.
  9. Disconnect the jumper harness from the transmission side of the transmission in-line 20-way connector. Connect the transmission in-line 20-way connector. Disconnect the PCM connector C2. Measure the resistance of the PC solenoid circuit from the PCM harness connector C2 terminal No. 45 to 46. Does the resistance measure 3-7 ohms? If so, go to step  13 . If not, go to next step.
  10. Does the resistance measure greater than 7 ohms? If so, go to next step. If not, go to step  12 .
  11. Test the PC solenoid valve high (1228) and low (1229) control circuits for an open between the PCM and the transmission in-line 20-way connector. Did you find and correct the condition? If so, go to step  17 .
  12. Test the PC solenoid valve high (1228) and the low (1229) control circuits for a short together between the PCM and the transmission in-line 20-way connector. Did you find and correct the condition? If so, go to step  17 .
  13. Test the PC solenoid valve high (1228) and low (1229) control circuits for a short to ground or short to power between the PCM and the transmission in-line 20-way connector. Did you find and correct the condition? If so, go to step  17 . If not, go to step  16 .
  14. Replace the pressure control solenoid valve. See SOLENOID VALVES  under REMOVAL & INSTALLATION. Did you complete the replacement? If so, go to step  17 .
  15. Replace the transmission internal wiring harness assembly. See TRANSMISSION INTERNAL WIRING HARNESS  under REMOVAL & INSTALLATION. Did you complete the replacement? If so, go to step  17 .
  16. Replace the PCM. See POWERTRAIN CONTROL MODULE  under REMOVAL & INSTALLATION. Did you complete the replacement? If so, go to next step.
  17. Perform the following procedure in order to verify the repair:
    • Select DTC.
    • Select CLEAR INFO.
    • Start the engine.
    • The PC solenoid valve actual current must be between 0.1 and 1.1 amp.
    • Select SPECIFIC DTC.
    • Enter DTC P0748.

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

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