Before testing sensors, you must verify the ECU is receiving clean power and has solid grounds. Switched +12V power from the EFI main relay.
On older Toyota ECUs like the 4S-FE, you don't need a modern OBDII scanner to read codes. 4s-fe ecu pinout
Because the 4S-FE shares much of its architecture with the larger , their ECU layouts are often nearly identical, typically featuring a 26-pin and 16-pin (or 22-pin) connector configuration. Core ECU Pin Functions Before testing sensors, you must verify the ECU