What could cause my 2023 Toyota Highlander to have a rough transmission shift?

Possible Causes

• Low or contaminated transmission fluid.
• Faulty transmission control module (TCM).
• Failing transmission solenoids or sensors (e.g., speed sensor, pressure sensor).
• Mechanical issues within the transmission (e.g., worn clutch packs or valves).
• Software issues affecting shift points and timing.

Repair Instructions

1. If Fluid Level is Low or Contaminated

• Step 1: Drain the old transmission fluid using a drain pan.
• Step 2: Replace the transmission filter if applicable.
• Step 3: Refill with the appropriate type and amount of new transmission fluid (refer to the owner's manual for specifications).

2. If Faulty TCM or Software Update is Required

• Step 1: If testing reveals a faulty TCM, remove the TCM following the service manual instructions.
• Step 2: Install the new TCM by reversing the removal steps.
• Step 3: If a software update is available, connect the vehicle to the diagnostic tool and follow the prompts to update.

3. If Solenoids or Sensors are Faulty

• Step 1: Identify which solenoid or sensor is defective based on DTCs.
• Step 2: Remove the transmission pan (if necessary) to access the affected solenoid or sensor.
• Step 3: Replace the faulty component with a new one.
• Step 4: Reinstall the pan and refill the transmission fluid as needed.

4. If Mechanical Issues are Suspected

• Step 1: Consult the service manual for the specific mechanical issue.
• Step 2: If internal components are worn (clutch packs, gears), a complete transmission rebuild or replacement may be necessary.
• Step 3: Follow the manual for disassembly, inspection, and replacement of internal components.

Final Steps

1. Test Drive: After repairs, take the vehicle for a test drive to ensure that the rough shifting issue has been resolved.
2. Clear Codes: If DTCs were present, clear them using the OBD-II scanner and monitor for reoccurrence.

By following these diagnostics and repair steps, you should be able to identify and resolve the rough transmission shift issue in your 2023 Toyota Highlander. Always refer to the specific service manual for your vehicle for detailed instructions and torque specifications.