Reasons for the absence of torque converter locking in the AL4 automatic transmission:
Lock Solenoid:
* Faulty lockout solenoid
* Worn or damaged solenoid plunger
* Blocked or dirty solenoid coil
Blocking valve:
* Stuck or worn lock valve
* Insufficient oil pressure
Interlock control circuit:
* Faulty transmission temperature sensor
*Faulty Transmission Control Module (TCM)
* Damaged electrical wiring
Lockup clutch slip:
* Worn or damaged lock-up clutch
* Insufficient oil pressure
Other possible reasons:
*Low transmission fluid level
* Contaminated transmission fluid
* Worn bearings
* Worn gears
Diagnosis and solution:
* Connect the scanner to the car and read the fault codes.
* Check the level and condition of the transmission fluid.
* Measure the transmission oil pressure.
* Check the lockout solenoid and plunger for wear or damage.
* Inspect the lock valve and replace it if necessary.
* Check the interlock control circuit and replace faulty components.
* Replace the lock-up clutch if necessary.
* Overhaul the transmission to replace worn components.