If the battery voltage falls below a minimum level, these memories are cleared and the TCM determines that there is a malfunction in the power supply circuit. When the engine is next started, the TCM will illuminate the MIL and set the DTC.this process determines the absence of a power source or ground, then perform a continuity test to check the integrity of the wiring, ignition switch, and other components. Continuity test must be performed with the power removed from the circuit while reading for wiring.