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

Toyota Highlander Fourth Generation (2020-present)

Error Codes

1-2 hours

Time

medium

Difficulty

high

Severity

Error Code: B1681

3 min read

538 words

⚠️ Safety Warning

This issue requires immediate attention. If you are not experienced with automotive repairs, consult a professional mechanic. Working on critical systems can be dangerous.

Problem Statement

Learn how to diagnose and fix B1681 keyless entry issues in Toyota Highlander. Step-by-step guide with diagnostic procedures and repair instructions.

Error Code

B1681

Affected Component

Electrical

Estimated Time

1-2 hours

⚠️ Safety Warnings

Important safety information - read before proceeding

•Disconnect the battery before working on electrical systems to avoid shorts.
•Allow the vehicle to sit for a few minutes after disconnecting the battery before handling any components.

Symptoms

•Keyless entry system not functioning
•Vehicle not starting or intermittent starting issues
•Security light illuminated on the dashboard
•Difficulty detecting the Smart Key fob
•Warning message on the display about the key fob

Diagnostic Steps

1
Scan the vehicle with an OBD-II scanner to confirm the B1681 code and check for any additional codes.
2
Inspect the Smart Key fob for physical damage, low battery, or malfunction.
3
Check the Smart Key ECU connections for corrosion or looseness.
4
Verify that the vehicle's battery is fully charged and in good condition.
5
Test the Smart Key fob battery voltage with a multimeter to ensure it meets specification.
6
Inspect the vehicle's wiring harness related to the keyless entry system for any visible damage or wear.

Solution

💡 Expert Tip

For complex repairs like this, consider taking photos at each step. This helps if you need to reverse a step or consult with a mechanic. Also, keep all removed parts organized - you may need to reference them during reassembly.

Verification

After completing the repair, verify that the issue has been resolved:

✓Test the affected component to ensure it functions correctly
✓Check for any error codes or warning lights
✓Monitor the vehicle for a few days to ensure the issue does not recur

Prevention Tips

To prevent this issue from occurring again:

•Follow the manufacturer's recommended maintenance schedule
•Address warning signs early before they develop into major issues
•Use quality parts and fluids recommended for your vehicle
•Keep detailed records of all repairs and maintenance

Tools & Equipment Required

•OBD-II scanner
•Multimeter
•Small flathead screwdriver
•Electrical contact cleaner
•Replacement battery (CR2032)
•Torque wrench

Parts Required

•Smart Key fob battery (CR2032)
•Smart Key ECU (if replacement is necessary)

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Diagnostic Steps

1
Scan the vehicle with an OBD-II scanner to confirm the B1681 code and check for any additional codes.
2
Inspect the Smart Key fob for physical damage, low battery, or malfunction.
3
Check the Smart Key ECU connections for corrosion or looseness.
4
Verify that the vehicle's battery is fully charged and in good condition.
5
Test the Smart Key fob battery voltage with a multimeter to ensure it meets specification.
6
Inspect the vehicle's wiring harness related to the keyless entry system for any visible damage or wear.

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

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

3. Inspect and Clean Smart Key ECU Connections

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

4. Test Smart Key System

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

5. Replace Smart Key ECU (if necessary)

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