Engine Control Module

The Engine Control Module (ECM) microprocessor receives input signals from various sensors, switches, and ignition and starting system components. The ECM uses this information for controlling various functions. See OUTPUT SIGNALS under COMPUTERIZED ENGINE CONTROLS. The ECM has constant battery voltage at BATT terminal. The EFI main relay provides battery voltage to +B and +B1 terminals of ECM when ignition is turned on.

The ECM contains a fail-safe function, used in case of sensor or switch failure. Fail-safe function uses preprogrammed values to provide a limp-in mode for minimal driveability. If a failure exists, ECM will inform the driver by turning on Malfunction Indicator Light (MIL) on the instrument panel.

NOTE: The MIL light may also be referred to as the CHECK ENGINE light.

The ECM is equipped with a self-diagnostic function. Diagnostic trouble codes may be set by the malfunction of various engine sensors, switches or circuits, and stored in the ECM memory. When diagnostic trouble code is stored, Malfunction Indicator Light (MIL) on instrument panel will come on.

ECM LOCATION

Model	Location
Tercel	Bottom Center Of Dash, In Front Of Console

NOTE: Components are grouped into 2 categories. First category is INPUT DEVICES, which covers components that control or produce voltage signals monitored by the Engine Control Module (ECM). Second category is OUTPUT SIGNALS, which are components controlled by the ECM.