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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 P0778: Pressure Control Solenoid "B" Electrical >> 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. Install the scan tool. Turn ignition on, engine off. Record the DTC failure records. Start the engine. Using the scan tool, check ignition voltage. Is the voltage 9-18 volts? If so, go to next step. If not, see DTC P0562: SYSTEM VOLTAGE LOW  or DTC P0563: SYSTEM VOLTAGE HIGH  .
    3. NOTE: Duty cycle value of 75 percent is an indication that the solenoid is in the ON state.
  3. Turn ignition on, engine off. Using scan tool, command solenoid "B" on. Did the scan tool indicate solenoid "B" was ON? If so, see DIAGNOSTIC AIDS . If not, go to next step.
  4. Turn ignition off. Disconnect C2 connector from the TCM, and install Breakout Box (J-39700) and Breakout Box Adapter (J-43799). Measure the resistance between TCM connector C2 terminals No. 24 and 25. See COMPONENT RESISTANCE  under ELECTRONIC COMPONENT SPECIFICATIONS. Is the resistance reading within the specified range? If so, go to next step. If not, go to step  6.
  5. Turn ignition on, engine off. Using DVOM, measure voltage between connector TCM connector C2 terminals No. 24 and 25. Using the scan tool, command solenoid "B" on. Is voltage 5-13 volts when the solenoid is on? If so, go to step  6. If not, go to step  11.
  6. Turn ignition off. Disconnect the transmission in-line 20-way connector. Measure the resistance between transmission in-line 20-way connector terminals "N" and "P". See COMPONENT RESISTANCE  under ELECTRONIC COMPONENT SPECIFICATIONS. Is the resistance within the specified range? If so, go to next step. If not, go to step  8.
  7. Repair the vehicle wiring harness. Is the repair complete? If so, go to step  12.
  8. Remove the oil pan. See appropriate AUTOMATIC article in TRANSMISSION SERVICING. Disconnect internal wiring harness at solenoid "B". Measure the resistance of solenoid "B". See COMPONENT RESISTANCE  under ELECTRONIC COMPONENT SPECIFICATIONS. Is the solenoid resistance within the specified value? If so, go to next step. If not, go to step  10.
  9. Replace the internal wiring harness. See TRANSMISSION INTERNAL WIRING HARNESS  under REMOVAL & INSTALLATION. Is the replacement complete? If so, go to step  12.
  10. Replace solenoid "B". See SOLENOID VALVES  under REMOVAL & INSTALLATION. Is the replacement complete? If so, go to step  12.
    11. CAUTION: In most cases, the TCM is not at fault. Investigate thoroughly before replacing the TCM.
  11. Replace the TCM. See TRANSMISSION CONTROL MODULE  under REMOVAL & INSTALLATION. Is the replacement complete? If so, go to next step.
  12. Perform the following procedure to verify the repair:
    • Clear the DTC.
    • Drive the vehicle under normal operating conditions.
    • Using the scan tool, monitor the operation of solenoid "B".

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

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