Diagnosing GM Converter Lock-Up Problems

Test #6 (Regular Method)

Check for ground at terminal D at the transmission.

1. On Non-computer-controlled vehicles skip this test and go directly to cooler line pressure, or surge test.
2. Raise the vehicle on the lift so the driving wheels are off the ground.
3. Unplug the wires at the case and connect the alligator clip of your test light to terminal A.
4. Place the tip of your test light on terminal D.
5. Start the engine and bring to normal operating temperature.
6. Place the selector in Drive. (O.D. on four speed units).
7. Accelerate slowly to 60 mph and the tester should light.
8. If the tester does not light you have a computer system problem. Go to test # 7 (Regular Method).

Test #6 (Quick Method)

Check for ground at terminal D at the ALDL

Note: First you must have passed ALDL Quick method (Test # 1. Otherwise continue with regular method Test # 6).

1. The test light should still be connected between terminal A and F at the ALDL.
2. With the engine at normal operating temperature, go for a road test
3. As you start your road test the tester should be lit.

   Note: If your foot is on the brake the light will be out.

4. Watch the test light to see if it goes out at some point during the road test
5. If the test light goes out, you have ground at terminal D at the transmission. Go to test # 7.
6. If the test light stays on you have a computer system problem. (See test # 13) Go test # 7.

Test #7 (Regular Method)

Ground the D wire at the transmission

1. Shave a little insulation from or pierce the D wire near the transmission connector. Reseal with silicon.
2. Connect one end of a jumper wire to the bare wire you just shaved or pierced.
3. Connect the other end of the jumper wire to ground.
4. Road test for lock-up (can be done on lift).
5. If you're not sure if lock-up occurred, then hold a steady speed of 60 mph (on the lift) and lightly touch and release the brake. You should feel lock-up disengage and re-engage.

Test #7 (Quick Method)

Ground the D wire at the ALDL

Note: You must first have passed ALDL Quick method (Test # 1).

1. Connect one end of a test light or jumper wire to terminal A at the ALDL.
2. Go for a road test. (This can also be done on the lift)
3. At approximately 35 mph, connect the other end of the test light or jumper wire to terminal F at the ALDL. The torque converter should Lock-up.
4. Whether the T/C locks up or not, follow the trouble-shooting tree to the next step, cooler line surge test.

Page 1   Page 2   Page 3   Page 4   Page 5   Page 6