Theory Of Operation

The purpose of the diagnostic is to detect the reason of a Transmission Control Module (TCM) reset. The reason is determined after a reset following TCM re-initialization. There are several situations where a reset of the TCM can occur. Some of these are initiated by the TCM software itself and others may be caused by an under voltage condition. There are three reset categories which include low level software, high level / application software and under voltage conditions. The following failures are examples of each of these categories that can cause resets of the TCM:

• A function call is out of sequence in the high level / application software.
• A division by zero has occurred in the low level software.
• An under voltage condition has occurred in the TCM supply voltage.

If the software detects a condition for initiating a reset, the reason of the reset is stored in an area of the Random Access Memory (RAM) that is not initialized (non volatile) during TCM initialization. Upon TCM re-initialization, this information is read and the appropriate DTC indicating the reason for the reset is stored.