Contents: Electronic control system ⇊ Emergency operation mode ⇊ Duplication function ⇊ Self-diagnosis function ⇊ Logic diagram of detection from two…⇊
Electronic control system
In vehicles with a manual transmission, the engine control unit (ECM) is responsible for the operation of the engine's fuel system and the exhaust toxicity reduction system; in vehicles with an automatic transmission, the powertrain control unit (PCM) is responsible.
Emergency operation mode
When an abnormal signal is sent to the ECM/PCM from any sensor, the signal is not accepted by the system and the pre-programmed value for that sensor is used instead, allowing the engine to continue running.
Duplication function
When a fault occurs in the ECM/PCM itself, fuel injector control switches to a backup circuit independent of the system to allow the driver to reach the nearest service station.
Self-diagnosis function
When an abnormal signal is sent to the ECM/PCM from any sensor, the ECM grounds the MIL circuit and stores a DTC in the rewritable memory. When the ignition switch is first turned to the ON position, the ECM/PCM grounds the MIL lamp for two seconds and checks for lamp operation.
Logic diagram of detection from two trips
To avoid false indications, some self-diagnostic functions use a "two-trip detection method". When a malfunction is detected, the ECM/PCM stores the malfunction code in memory. When the same malfunction occurs again after turning the ignition switch OFF and ON (II) again, the ECM/PCM informs the driver by illuminating the MIL.