How do I troubleshoot the transmission shifting issues in a 2020 Toyota Highlander?

Troubleshooting Transmission Shifting Issues in a 2020 Toyota Highlander

Step 1: Gather Tools and Equipment

Before starting the diagnosis, ensure you have the following tools and equipment:

• OBD-II scanner
• Torque wrench
• Socket set (including extensions)
• Screwdrivers (flat and Phillips)
• Transmission fluid dipstick (if applicable)
• Clean rags or towels
• Transmission fluid (Toyota ATF WS)
• Safety gloves and goggles

Step 2: Check for Diagnostic Trouble Codes (DTCs)

1. Connect the OBD-II Scanner: Locate the OBD-II port (usually under the dashboard near the driver's seat) and plug in the scanner.
2. Read Codes: Turn the ignition to the "On" position without starting the engine, and read any stored codes related to transmission issues.
3. Interpret Codes: Refer to the scanner’s manual or an online database to interpret the codes. Common transmission-related codes may include P0700 (Transmission Control System Malfunction) or specific solenoid codes.

Step 3: Inspect Transmission Fluid

1. Check Fluid Level:
   • With the engine warmed up and running, locate the transmission fluid dipstick.
   • Remove the dipstick, clean it with a rag, and reinsert it fully. Remove it again to check the fluid level. It should be between the "Full" and "Add" marks.
2. Check Fluid Condition:
   • Assess the fluid color and smell.
   • Healthy ATF is typically red and has a slightly sweet smell. Dark brown or burnt-smelling fluid indicates it needs to be replaced.

Step 4: Inspect for Leaks

• Visually check under the vehicle and around the transmission for any signs of fluid leaks. Look for wet spots or stains, and check the condition of the transmission pan, seals, and gaskets.

Step 5: Examine Electrical Connections

1. Inspect Wiring: Look for damaged or frayed wiring connected to the transmission control module (TCM) and solenoids.
2. Connector Checks: Ensure that all connectors are seated properly and free of corrosion.

Step 6: Test the Transmission Control Module (TCM)

1. Perform a TCM Reset:
   • Disconnect the battery (remove the negative terminal) for about 10 minutes. This can reset the TCM.
   • Reconnect the battery and check if the issue persists.
2. Check TCM Signals: If the problem continues, use a scan tool to monitor TCM parameters and perform a functional test.

Repair Instructions

Step 1: Replace Transmission Fluid (if necessary)

If the fluid is burnt or low:

1. Drain the Old Fluid: Place a drain pan under the transmission pan and remove the pan bolts to drain the fluid completely.
2. Replace the Filter: If applicable, replace the transmission filter.
3. Reinstall the Pan: Torque the pan bolts to the manufacturer’s specifications.
4. Refill with New ATF: Using a funnel, refill with the correct type of transmission fluid (Toyota ATF WS) through the dipstick tube.

Step 2: Replace Faulty Components

If diagnostics indicate specific solenoid or sensor failures:

1. Replace Solenoids: Remove the transmission pan and access the solenoids. Disconnect electrical connectors and remove bolts to replace faulty solenoids.
2. TCM Replacement: If the TCM is found faulty, follow the manufacturer’s service manual for removal and installation.

Step 3: Recheck and Test Drive

1. Reconnect Battery: If disconnected, reconnect the negative battery terminal.
2. Start the Engine: Allow the vehicle to warm up and check for proper fluid circulation.
3. Test Drive: Take the vehicle for a test drive to confirm that shifting issues have been resolved.

Final Steps

If the transmission shifting issues persist after performing the above troubleshooting and repairs, it may require a professional inspection. A transmission specialist can perform more in-depth diagnostics, such as internal inspections and advanced electronic tests.

Conclusion

Troubleshooting transmission issues can be complex, but following these steps should help identify and resolve common problems. Always refer to the manufacturer’s service manual for specifications and detailed procedures. If unsure at any point, do not hesitate to consult with a qualified automotive technician.