Engine Off Timer Monitoring
14 Engine Off Timer MonitoringGeneral description
The engine off time calculation is based on the received CAN information from instrument cluster control, which cumulates all the time while ignition key is off.
Diagnosis at power up of the engine control unit
After a power up of the engine control unit the received ignition key off time is checked against the total power latch time of the ECU since last engine run. The ECU power latch time is stored in the non volatile memory. The received ignition key off time must not be shorter than the cumulated ECU power latch time since last engine run.
Flow chart
Diagnosis at ignition key on during power latch time
In case of ignition key is switched on during the ECU power latch phase (ECU is still running) the received ignition key off time is compared with the power latch time of the ECU. The ECU power latch time counts until the end of power latch phase (in this case finished by ignition key equal to on). The received ignition key off time must be in a tolerance range of the ECU power latch time since last engine run (two sided rationality check for too long or too short engine off time signal).
Flow chart
Diagnosis of reset counter of the instrument cluster
The instrument cluster sends to the engine control unit a information for battery disconnect. With every ignition key on transition after a successful engine run this information is monitored by the ECU. If the signal is true (battery disconnection detected by instrument cluster) a counter is incremented. If the counter exceeds a threshold, the information from instrument cluster is marked as not plausible.
Flow chart
