Starter signal used to let the ECU know the engine is cranking.
(though this can vary by specific model year, such as the 1997–2001 Corolla). The ECU acts as the central brain, monitoring inputs from sensors like the throttle position, oxygen, and water temperature to manage fuel injection and ignition timing. International Automotive Technicians Network - iATN Key ECU Terminals and Functions toyota 4afe ecu pinout
The ECU typically has three connectors: (16-pin), B (10-pin), C (10-pin). Below is the functional list. Starter signal used to let the ECU know