Search for forums focusing on "Toyota 89661-xxxxx pinout" specifically. 5. Tools for Working with Toyota ECU Pinouts

Before attempting to use a pinout, the specific unit must be identified. A part number starting with 89661 is always an ECU, but the suffix dictates the vehicle and wiring.

INJ1-4 (Injectors), IGT1-4 (Coil Triggers), IAC1-2 (Idle Air Control).

Usually consists of 2 to 3 yellow or grey plastic connectors directly plugging into the ECU board. Pins are typically arranged in two rows per plug.

Saves significant money by enabling board-level repairs instead of total replacement. :

Looking at the back of the plug where the wires enter.

The W pin (Warning light) functions as a ground switch. To wire a custom check engine light, connect one side of a 12V bulb to a switched 12V source, and connect the other side directly to the W pin on the ECU.

Measure voltage between VC and E2 with the ignition on. If it does not read exactly 4.5V to 5.5V, the ECU is either missing power, missing a ground, or an external sensor is shorted internally and pulling the voltage down.

Look at the base of the plug pins on both sides of the circuit board. Toyota routinely prints the labels ( +B , BATT , E1 , etc.) directly on the board.

Unswitched, constant 12V power direct from the battery via a fuse. This maintains the ECU’s temporary memory, storing Diagnostic Trouble Codes (DTCs) and fuel trim learning data.