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Home >> GMC >> 1991 >> Value Van 7.4 N >> Repair and Diagnosis >> Transmission >> Automatic Trans >> Diagnosis - A/T >> Service Bulletins >> No Lock-Up Condition

No Lock-Up Condition

  1. Does TCC release with brake switch? If yes, go to step 3). If no, check brake switch. See BRAKE SWITCH TEST . If brake switch is okay, check TCC apply solenoid. See TCC APPLY SOLENOID TEST . If solenoid is okay, check for stuck lock-up apply valve or lock-up apply valve installed backward. Repair as necessary and retest.
  2. If apply valve is okay, block lock-up apply valve in unlocked position. If TCC still does not release, problem is located in torque converter or oil pump. If lock-up does not occur, check appropriate signal oil circuit.
  3. If TCC released in step 1), check for short to ground at terminal "D" wire of ALDL connector. See Figure. If short is found, check apply solenoid. See TCC APPLY SOLENOID TEST . If short is not found, check for computer system problem. See CHECKING SELF-DIAGNOSTIC SYSTEM.
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