Troubleshooting Transmission Issues in a 2020 Toyota Highlander (Fourth Generation)

Step 1: Visual Inspection

• Tools Required: Flashlight, gloves, diagnostic scanner (OBD-II).
• Check the transmission fluid level and condition.
  • Action: Locate the transmission dipstick (if applicable) and remove it. Wipe it clean, reinsert, and check the fluid level and color (should be a bright red color).
  • Action: Inspect for any fluid leaks around the transmission pan, seals, and cooler lines.

Step 2: Scan for Diagnostic Trouble Codes (DTCs)

• Tools Required: OBD-II scanner.
• Action: Connect the OBD-II scanner to the vehicle’s diagnostic port (usually located under the dashboard).
• Action: Retrieve any stored DTCs related to the transmission. Common codes include P0700 (Transmission Control System Malfunction) and other specific transmission codes.

Step 3: Test Drive the Vehicle

• Action: Drive the vehicle under various conditions (city, highway, and incline).
• Observation: Note any issues such as slipping, delayed engagement, or unusual noises during shifting.

Step 4: Check Electrical Connections

• Tools Required: Multimeter, socket set.
• Action: Inspect the wiring and connectors to the transmission control module (TCM) and the transmission solenoids for signs of wear, corrosion, or damage.
• Action: Use a multimeter to check the voltage and ground at the connectors to ensure proper power supply.

Step 5: Fluid Condition Analysis

• Tools Required: Fluid analysis kit, clean container.
• Action: If the fluid is dark, burnt, or contaminated, it may need to be replaced.
• Action: Check for metal shavings or debris in the fluid, indicating internal wear.

Repair Instructions

Repair 1: Transmission Fluid Change

Tools Required:

• Transmission fluid (Toyota WS)
• Transmission fluid pump
• 10mm socket and ratchet
• Clean container for old fluid
• Funnel

Steps:

1. Raise the Vehicle:

   • Use a jack and jack stands to safely elevate the vehicle.

2. Drain Old Fluid:

   • Locate the transmission drain plug and remove it using a 10mm socket.
   • Allow the fluid to drain into a container.

3. Replace Filter (if applicable):

   • If your model has a replaceable filter, remove the transmission pan and filter, then install the new filter.

4. Reinstall Drain Plug:

   • Replace the drain plug and tighten it to the manufacturer's specifications.

5. Refill New Fluid:

   • Use a funnel to refill the transmission with the appropriate type and amount of fluid (Toyota WS).
   • Start the engine and allow it to reach operating temperature, then check the fluid level again and add if necessary.

Repair 2: Electrical Connection Repair

Tools Required:

• Multimeter
• Soldering iron (if repairing wires)
• Electrical tape or heat shrink tubing

Steps:

1. Identify Faulty Connections:

   • Based on the previous diagnosis, identify any damaged wiring or connectors.

2. Repair or Replace:

   • For damaged wiring, splice in new wire and solder connections. Use electrical tape or heat shrink tubing to insulate.
   • Replace any corroded connectors with new ones.

3. Test After Repair:

   • Reconnect everything and test drive the vehicle to ensure that the issue has been resolved.

Repair 3: TCM Reprogramming or Replacement

Tools Required:

• OBD-II scanner with reprogramming capability
• Replacement TCM (if necessary)

Steps:

1. Reprogram TCM:

   • If DTCs indicate a TCM issue, follow manufacturer instructions for reprogramming using the OBD-II scanner.

2. Replace TCM:

   • If the TCM is determined to be faulty, disconnect the battery, remove the old TCM, and install the new one.
   • Reconnect the battery and follow reprogramming instructions.

Conclusion

Following these diagnostic and repair steps will help you effectively troubleshoot and potentially resolve transmission issues in a 2020 Toyota Highlander. Always refer to the manufacturer’s service manual for specific torque specifications, fluid capacities, and detailed repair procedures. If the issue persists after these steps, consult a professional technician for further diagnosis.