Theory Of Operation

The purpose of the shut down timer diagnostic is to determine if the Powertrain Control Module (PCM) internal clock is running as expected. This engine off timer is used as an enable condition for various OBD monitors. The rationality test consists of two tests used to evaluate shut down time.

During an initial engine start, if it is determined that the engine start is a cold start (determined by comparing the engine coolant temperature versus ambient temperature), the

Slow Test 

will be run and a long shut down time would be expected. If it is determined that the engine start is not a cold start, the

Fast Test 

will be run and a short shut down time is expected because the engine has not been cooled down to cold start conditions.

• The P1607 DTC will set if the Slow Test diagnostic runs and fails.
• The P2610 DTC will set if the Fast Test diagnostic runs and fails.