|If you automatic transmission is acting erratically, may it be shifting too hard, shifting too late, shifting too early, etc. try the diagnostic to isolate the problem. The diagnostic, like the main computer diagnostic, may show an error code if it reads a sensor or circuit that is not within factory specs. If the problem is mechanical, the diagnostic won't show it. If it's electrical, then the diagnostic gives a general idea where to start looking to correct the performance.
1. Have the engine at normal operating temperature, in P with the overdrive switch on.
2. Start engine. The AT light (1.) should go out after 2 sec.
3. Turn the ignition off.
4. Move selector to drive D by using the Push Release button (2.). If not equipped, use the brake pedal
5. Set overdrive switch to OFF.
6. Wait 2 seconds and turn ignition switch ON.
7. Wait 2 seconds and move selector to 2.
8. Set overdrive switch to ON.
9. Move selector to 1.
10. Set overdrive switch to OFF.
11. Depress accelerator pedal fully and release it.
12. The codes will begin to flash. There�s one long flash that signifies the start of the sequence. Following should be 10 short flashes. Then it repeats.