How can I troubleshoot a Toyota Highlander with inconsistent shifting?

Troubleshooting Inconsistent Shifting in a 2020-Present Toyota Highlander (Fourth Generation, XU70)

Step 1: Initial Inspection

• Visual Check: Inspect the transmission fluid level and condition. Ensure it's at the proper level and is a bright red color; dark or burnt-smelling fluid indicates a problem.
• Check for Leaks: Look for any signs of fluid leaks around the transmission pan or seals.

Tools Required:

• Transmission fluid dipstick or funnel
• Clean rag
• Flashlight
• OBD-II scanner

Step 2: Scan for Error Codes

1. Connect OBD-II Scanner: Plug the scanner into the OBD-II port under the dashboard.
2. Read Codes: Check for any stored trouble codes related to the transmission.
3. Record Codes: Note any codes such as P0700 (Transmission Control System Malfunction) or others related to transmission sensors.

Step 3: Check Transmission Fluid

1. Fluid Level Check: With the engine running and the transmission in park, remove the dipstick and wipe it clean. Reinsert and remove again to check the level.
2. Fluid Condition: Inspect the fluid. If it’s dark or has a burnt smell, it may need to be replaced.

Repair Instructions

Step 4: Fluid Change (if necessary)

1. Gather Tools: You'll need a socket set, transmission fluid (check owner’s manual for specifications), and a fluid pump.
2. Raise Vehicle: Use jack stands to securely lift the vehicle.
3. Drain Fluid:
   • Place a drain pan under the transmission pan.
   • Remove the pan bolts and carefully lower it to drain the fluid.
4. Replace Filter (if applicable):
   • Remove the old filter and replace it with a new one.
5. Reinstall Pan: Clean the pan and reattach it with a new gasket.
6. Refill Fluid: Use a fluid pump to refill the transmission through the dipstick tube with the recommended fluid.

Step 5: Inspect Transmission Components

1. Check Solenoids: If error codes indicate solenoid issues, inspect and test them. Replace if faulty.
2. Inspect Transmission Control Module (TCM): Consider reprogramming or replacing if it’s not functioning correctly.

Step 6: Test Drive

1. Test Drive the Vehicle: After repairs, take the vehicle for a test drive to see if the shifting issues persist.
2. Monitor Performance: Pay attention to any delays or harsh shifts during the drive.

Conclusion

If the issue persists after checking and replacing the transmission fluid and inspecting key components, it may indicate a deeper mechanical issue within the transmission, such as worn clutches or internal failures. In such cases, it is recommended to consult with a professional technician or a Toyota dealership for further diagnostics and repairs.