With 4L80-E Transmission

When the TCM sets a code, the "Service Engine Soon" light will come "ON" and a code will be stored in memory. If the problem is intermittent, the light will go out after 10 seconds, when the fault goes away. However, the code will stay in the TCM memory for 50 starts, or until the battery voltage to the TCM is removed. Removing battery voltage for 30 seconds will clear all stored codes.

Codes should be cleared after repairs have been completed. Also, most diagnostic charts will tell you to clear the codes before using the chart. This allows the TCM to set the code while going through the chart, which will help to find the cause of the problem more quickly.

NOTICE To prevent TCM damage, the key must be "OFF," when disconnecting or reconnecting power to TCM (for example battery cable, TCM pigtail, "TCM-IGN" fuse,jumper cables, etc.).