how to fix B1681 code in Toyota Highlander Fourth Generation (2020-present)

Solution

1. Preparation

• Gather necessary tools and parts.
• Ensure the vehicle is parked on a level surface and the ignition is turned off.
• Disconnect the negative battery terminal to avoid electrical shorts.

2. Replace Smart Key Battery

1. Open the Smart Key fob using a small flathead screwdriver.
2. Remove the old battery and replace it with a new one (typically a CR2032).
3. Reassemble the fob and ensure it clicks shut securely.

3. Inspect and Clean Smart Key ECU Connections

1. Locate the Smart Key ECU, usually found under the dashboard or near the steering column.
2. Disconnect the wiring harness from the ECU.
3. Inspect the connectors for corrosion or dirt; clean with electrical contact cleaner if necessary.
4. Reconnect the wiring harness securely.

4. Test Smart Key System

1. Reconnect the negative battery terminal.
2. Attempt to start the vehicle with the Smart Key fob.
3. Use the OBD-II scanner to clear the B1681 code and observe if it reappears.

5. Replace Smart Key ECU (if necessary)

1. If the issue persists, remove the Smart Key ECU by unscrewing it from its mounting.
2. Disconnect any wiring harnesses.
3. Install the new Smart Key ECU by reversing the removal steps and ensure all connections are secure.