How to Test if Your Catalytic Converter is Functioning Properly

As an ASE-certified automotive technician, one of the most common questions I receive is – how can I test my catalytic converter? The catalytic converter is critical in reducing harmful pollutants from your vehicle’s exhaust emissions.

By using specialized coated materials inside the converter, chemical reactions transform toxic gases like carbon monoxide into less harmful compounds before being emitted into the air. But converters can become damaged over time and cease to treat emissions properly.

Testing your catalytic converter at regular intervals is essential to ensure it still functions adequately, and your vehicle remains emissions-compliant. In this comprehensive guide, I’ll outline common symptoms of a faulty Catalytic converter and various diagnostic tests that can be performed to evaluate converter performance.

Read More: Aftermarket Catalytic Converters: Pros and Cons

Signs of a Potentially Failing Catalytic Converter

Look for any of these warning signs that may indicate issues with your catalytic converter:

Reduced Engine Performance

A clogged or contaminated converter increases exhaust backpressure, which restricts engine power, acceleration, and fuel economy. Performance suffers.

Unusual Rattling Noises

Internal breakdown of the ceramic converter substrate can cause a loud rattling or shaking sound from the vehicle’s underside.

Sulfur Smell from the Exhaust

The rotten egg scent indicates sulfur accumulation on converter surfaces, reducing efficiency.

Increased Exhaust Smoke

White/blue smoke from the tailpipe points to oil or coolant burning from engine issues that overload and clog the converter.

Illuminated Check Engine Light

Onboard diagnostics detect lowered converter efficiency or oxygen sensor issues that trigger error codes and the check engine light.

Failed Emissions Test

A damaged converter allows increased levels of CO, hydrocarbons, and NOx to pass through, causing emissions test failure.

Regularly monitoring your vehicle for any of these warning signs helps catch catalytic converter problems early before increased damage occurs. But to fully evaluate the converter function, specific testing is required.

Read More: Debunking Common Myths About Catalytic Converters

Check Failing Catalytic Converter Using Onboard Diagnostics (OBD-II)

One of the fastest ways to check for catalytic converter issues is using an onboard diagnostics (OBD-II) scanner:

Retrieve Diagnostic Trouble Codes

Plug the scan tool into the OBD-II port under the dash. It will read and display any diagnostic trouble codes stored for the various emissions monitors.

Check Converter Efficiency Codes

Codes P0420 to P0424 indicate lower than threshold converter efficiency. P0430 specifically notes Bank 2 converter problems on V-engines.

Monitor Oxygen Sensor Readings

Oxygen sensor performance faults often accompany a failed converter. Monitor their switching activity and voltage readings.

Review Emissions Readiness Monitors

Unfinished or failed emissions monitors point to problems with the catalytic converter’s effectiveness.

While not definitive, OBD-II scan results help identify suspect converter issues for further diagnosis. Next, we’ll move under the vehicle for hands-on inspection.

Performing a Physical Catalytic Converter Inspection

A visual inspection of your catalytic converter may reveal external issues:

Locate the Converter

Follow the exhaust pipes underneath the vehicle to locate the catalytic converter, which resembles a small muffler.

Check for Damage

Look for dents, cracks, holes, or separation between the converter shell and interior substrate, which allows exhaust to bypass treatment.

Examine the Heat Shield

Ensure the protective heat shield is intact. Missing sections result in converter overheating and failure.

Assess Mounting Points

Damaged, loose, or missing mounting brackets/bolts undermine the structural integrity. This leads to cracking.

Look Inside the Outlet

Peer into the downstream outlet using a flashlight. Debris accumulation indicates substrate breakdown.

Signs of physical damage necessitate converter replacement to restore proper functionality and avoid further issues.

Read More: Direct Fit vs Universal Catalytic Converters: An In-Depth Comparison

Using a Temperature Analysis to Check Converter Function

Measuring temperatures along the converter with an infrared thermometer can indicate problems:

Allow the Engine to Warm Up

Get the converter hot by running the engine for several minutes before starting the test.

Take Inlet Temperature Reading

Point the infrared thermometer at the converter’s inlet pipe and record the temperature.

Take Outlet Temperature Reading

Similarly, measure the temperature at the converter’s downstream outlet pipe.

Compare Readings

A functional converter will show a temperature drop from inlet to outlet as the chemical reactions absorb heat. Little difference implies deactivated catalysts.

Check Along the Length

Also, compare temperatures along the converter casing. Hotspots may signify a clogged converter.

Noting the temperature variances and any extreme heat areas pinpoints contaminated or non-functioning zones within the converter.

Using a Vacuum Gauge to Identify Exhaust Restrictions

Monitoring the exhaust system vacuum with a vacuum gauge can also indicate a blocked catalytic converter:

Attach Gauge to the Intake

Use a rubber hose to connect the vacuum gauge to a port on the intake manifold or carburetor.

Interpret the Baseline Reading

A steady vacuum reading between 12-22 inches of mercury is regular, depending on engine specifications.

Rev the Engine

Have an assistant rapidly accelerate and decelerate the engine RPMs. Watch for fluctuations in vacuum pressures.

Evaluate Gauge Response

The vacuum should remain relatively stable on a healthy exhaust. Spiking pressures point to restrictions like a catalytic converter blockage.

Conduct Under Load

Repeat the test under engine load, such as driving up an incline. The spikes will become more pronounced as the system works harder.

Vacuum testing during RPM changes can identify exhaust restrictions requiring further diagnosis. Professional emissions testing is the next recommended step.

Professional Emissions Testing

To definitively evaluate catalytic converter function, professional emissions testing is advised:

Pollutants Analysis

Emissions tests measure the exact levels of hydrocarbons, carbon monoxide, and nitrogen oxides in the exhaust stream. Elevated levels compared to specifications indicate converter failures to treat emissions properly.

Tailpipe Probe Test

A probe fed into the tailpipe provides emissions measurements with and without the converter connected to isolate its pollutant reduction capabilities.

Dynamometer Testing

Emissions are measured across driving cycles on a dynamometer. It assesses the converter function under changing loads and conditions.

Baseline Comparison

Results are compared to emissions baselines from a fully functional converter. Failures to maintain at least 80% conversion efficiency diagnose faulty converters.

Professional emissions shops have the specialized tools to diagnose catalytic converter issues. Tap into their expertise when problems are suspected.

When To Seek Professional Diagnosis on Failing Catalytic Converter

While do-it-yourself tests provide helpful insight, consider seeking expert help when:

  • Check engine light remains illuminated with converter-related trouble codes
  • You lack the tools or knowledge for proper diagnostics
  • Temperature or vacuum tests indicate blocked or deactivated areas
  • Performance issues continue despite attempted repairs
  • The vehicle fails an emissions test at the state inspection station
  • Underlying drivability problems like misfires may be overloading the converter

The tests described in this guide provide a starting point for identifying potential catalytic converter failures. However, confirming problems through professional diagnostics is critical before making significant repairs.

Maintaining Your Catalytic Converter

Follow proactive maintenance practices to prolong the life of your converter:

  • Address check engine lights promptly to prevent further converter damage
  • Repair oil leaks, engine misfires, improper fuel trim, or other issues that contaminate or overload the converter
  • Avoid using leaded fuel or oils containing metallic additives that foul converter surfaces
  • Follow factory-recommended maintenance schedules for tune-ups, fluid changes, filters, etc. to maximize engine health
  • Keep an eye out for rattling heat shields or damaged mounting points that undermine the converter
  • Consider professional catalytic cleaning if converter temperatures start exceeding the normal operating range

Routine maintenance and responsible driving habits significantly impact catalytic converter lifespan. Prioritize addressing any warning signs early.

Conclusion on Failing Catalytic Converter

While catalytic converters are built to last over 100,000 miles for most vehicles, they remain susceptible to failure from issues like oil contamination, structural damage, and thermal breakdown over time.

Testing your catalytic converter through temperature analysis, vacuum readings, onboard diagnostics, and professional emissions evaluations provides valuable insight into its functionality. Watch for warning signs like check engine lights, rotten egg odors, and performance issues.

Addressing converter problems promptly helps avoid increased engine wear and more extensive repairs. Maintain your emissions control system diligently to ensure your vehicle continues running cleanly for years to come. Let me know if you need any help assessing your converter function.

Sharing Is Caring:

Leave a Comment

This site uses Akismet to reduce spam. Learn how your comment data is processed.