Before testing sensors, you must verify the ECU is receiving clean power and has solid grounds. Switched +12V power from the EFI main relay.
Primary computer grounds (usually bolted to the intake manifold or cylinder head). E1: The main internal ground for the ECU logic circuit. 4s-fe ecu pinout
The dedicated sensor ground circuit; never tap into this for high-current accessories. Ignition & Injection Signals Before testing sensors, you must verify the ECU