Permanent +12V feed from the battery for the ECU’s internal memory (Keep Alive Memory).
The 4S-FE ECU manages everything from ignition timing to fuel injection pulses. Below is a breakdown of the critical pins and their roles in the engine management system.
The dedicated sensor ground circuit; never tap into this for high-current accessories. Ignition & Injection Signals 4s-fe ecu pinout
Often integrated into the MAP sensor or air box to account for air density.
Before testing sensors, you must verify the ECU is receiving clean power and has solid grounds. Switched +12V power from the EFI main relay. Permanent +12V feed from the battery for the
A crucial "confirmation" signal sent back from the igniter to the ECU. If the ECU doesn't see IGF, it will cut fuel to prevent catalytic converter damage.
While most 4S-FE engines use a standard Toyota S-series wiring logic, variations exist between early (distributor) and late (distributorless/waste-spark) models. Always verify your specific ECU part number—usually a 10-digit number like —against a Toyota Terminal Guide to ensure you aren't looking at a 4E-FE or 5A-FE diagram, which look similar but have different pin assignments. The dedicated sensor ground circuit; never tap into
Locate the "Diagnostic" or "Check" connector in the engine bay. Bridge pins with a paperclip. Turn the ignition to ON (don't start the engine).
Primary computer grounds (usually bolted to the intake manifold or cylinder head). E1: The main internal ground for the ECU logic circuit.