FAULTBASE
Error CodesASKCars
© 2026 FAULTBASE
All rights reserved.
v2.0.0 • Production
ContactPrivacyImpressum
What are the signs of a failing catalytic converter in a 2020 Highlander? - Toyota Highlander
Home/Cars/Toyota/Highlander/Fourth Generation (2020-present)/What are the signs of a failing catalytic converter in a 2020 Highlander?

What are the signs of a failing catalytic converter in a 2020 Highlander?

Toyota Highlander Fourth Generation (2020-present)

Error Codes
2-4 hours
Time
medium
Difficulty
medium
Severity
Error Code: P0420
Navigation
ProblemSymptomsDiagnosisSolution
ProblemSymptomsDiagnosisSolution
4 min read
707 words

Problem Statement

Learn the symptoms, diagnostic steps, and repair instructions for a failing catalytic converter in a 2020 Toyota Highlander.

Error Code
P0420
Affected Component
catalytic converter
Estimated Time
2-4 hours

Symptoms

  • •Check Engine Light (CEL)
  • •Poor Engine Performance
  • •Decreased Fuel Efficiency
  • •Rattling Noise
  • •Sulfur Smell
  • •Dark Exhaust Smoke

Diagnostic Steps

  1. 1
  2. 2
  3. 3
  4. 4
  5. 5

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
  • •Infrared thermometer
  • •Manifold pressure gauge
  • •Basic hand tools (ratchet set, sockets, wrenches)
  • •Safety goggles and gloves
  • •Jack and jack stands or a lift

Additional Information

Error Code
P0420
Affected Component
catalytic converter
Estimated Time
2-4 hours
Difficulty
medium
Severity
medium
Tools Required
6 items

Related Faults

Loading...

Share this solution

Comments

Sign in to share your thoughts

Sign In

No comments yet

Be the first to share your thoughts

Back to Generation
Signs of a Failing Catalytic Converter in a 2020 Toyota Highlander
Tools Required
  • OBD-II scanner
  • Infrared thermometer
  • Manifold pressure gauge
  • Basic hand tools (ratchet set, sockets, wrenches)
  • Safety goggles and gloves
  • Jack and jack stands or a lift
Repair Instructions

Step 1: Confirm the Diagnosis

  • Use the OBD-II scanner to check for codes, particularly P0420 or related codes. Make a note of any other codes present, as they might provide additional context.

Step 2: Conduct a Visual Inspection

  • Safely lift the vehicle and inspect the catalytic converter for any damage or signs of overheating. Ensure that the exhaust system is intact.

Step 3: Measure Exhaust Backpressure

  • Attach the manifold pressure gauge to the exhaust system before the catalytic converter. Start the engine and measure backpressure at 2,500 RPM. If it exceeds 2.5 psi, the catalytic converter may be clogged.

Step 4: Perform a Temperature Test

  • Measure the temperature at the inlet and outlet of the catalytic converter. If the outlet temperature is not significantly higher than the inlet, the converter may be failing.

Step 5: Evaluate Fuel Trim Values

  • Check the long-term fuel trim values via the OBD-II scanner. If they are excessively positive, it may indicate a rich mixture due to exhaust restrictions.

Step 6: Replace the Catalytic Converter (if necessary)

  1. Preparation

    • Ensure the engine is cool. Disconnect the battery and elevate the vehicle safely.

  2. Remove the Old Converter

    • Loosen and remove the exhaust clamps and bolts securing the catalytic converter to the exhaust system. If necessary, use penetrating oil on rusty bolts.

  3. Install New Converter

    • Place the new catalytic converter in the same position as the old one. Secure it with new gaskets and bolts as per manufacturer specifications.

  4. Reassemble Exhaust System

    • Reconnect any clamps and exhaust pipes removed during the process.

  5. Reconnect Battery

    • Reconnect the battery terminals and ensure all connections are secure.

  6. Clear Codes and Test Drive

    • Use the OBD-II scanner to clear any codes. Perform a test drive to ensure proper operation and check for any lingering issues.
Conclusion

A failing catalytic converter can lead to significant performance issues and increased emissions. Following these diagnostic and repair steps can help pinpoint the issue and restore normal function to your 2020 Toyota Highlander. If unsure about any step, consult a professional automotive technician for assistance.