4s-fe Ecu Pinout !!install!! < 2026 Update >

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.

On older Toyota ECUs like the 4S-FE, you don't need a modern OBDII scanner to read codes.

Before testing sensors, you must verify the ECU is receiving clean power and has solid grounds. Switched +12V power from the EFI main relay.

Monitors engine heat to adjust fuel trim and idle speed.

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.