The Typical Toyota Ignition System consists of spark plugs, ECM (engine control module), igniter, ignition coil, cap and rotor, ignition switch, fuse and battery. The electronic ignition system uses the Engine Control Module (ECM) for determining ignition timing (spark advance). The ECM determines ignition timing (spark advance) based on various input signals. Following input signals may be used: engine coolant temperature sensor, throttle position signal, oxygen sensor, engine RPM, vehicle speed sensor, A/C switch, brakelight signal, airflow meter, knock sensor, electrical load, MAP sensor and cranking (starter) signal. Input signals may vary on model application. Integrated (ignition coil on distributor) and remote ignition coil designs are used depending on model. Below schematic and wiring diagram shows Typical Toyota Ignition System for 1994 Celica.
Crankshaft position and engine RPM input signals are delivered to the ECM by 2 pick-up coils in the distributor. Crankshaft position input signal is delivered to G, G+ or G1 (and G2 on some models) terminal of ECM, and engine RPM input signal is delivered to NE or NE+ terminal of ECM. ECM uses pick-up coil input signals to switch primary ignition circuit on and off. Primary circuit is turned off when ECM delivers a signal to igniter on the IGT wire, causing ignition coil to fire the spark plug. After delivering a command to turn off primary circuit on the IGT wire, the ECM monitors IGF circuit to ensure primary switching occurred.