Select Your Vehicle

Harvest The Deals With Up To 30% Off MSRP

International Orders

International Customers, please review our international shipping policies for placing orders and to know more about Shipping, Payment, and Warranties.


Our USA based
parts pros can help.

Click Here

Industry Leading Warranty

Click to learn more


Home >   How To >   How to Repair Catalytic Converter >   Six Steps to Diagnosing a Bad Catalytic Converter

Six Steps to Diagnosing a Bad Catalytic Converter


A catalytic converter is a component that aids in reducing the level of pollutants present in the vehicle's exhaust gases. The by-products of combustion, when left unfiltered will be detrimental to the environment. As with other components of the vehicle, the cat converter may fail, requiring it to be addressed immediately.



Catalytic Converter


Generally, when any of the car parts go bad, they trigger an error code. Each error code indicates a specific problem. A P0420 or P0430 engine code indicates that there is some problem with the catalytic converter. This page explains how to go about diagnosing a bad catalytic converter using a scanning tool. The following steps can be performed to ensure that your catalytic converter's at fault:


Step 1


Test drive the vehicle. Check whether your car hesitates or stumbles. This may be due to fuel or ignition problems such as spark knocks or engine misfires.


Step 2


Start the vehicle and inspect the tail pipe. Check whether the exhaust system emits colored smoke such as black, blue or white. These smoke colors are indicative of engine-related problems:


Oil burning: blue

Internal coolant leak: white

Rich running conditions: black


Step 3


Do a thorough check to find any signs of vacuum or exhaust leaks. In addition, perform a complete visual inspection of your vehicle's ignition, fuel and intake components.


Step 4


Scan Tool Test: Do not clear codes until the 'Freeze Frame' information is retrieved. The scan tool will provide you with a list of details such as the vehicle's temperature, speed, load and throttle position when the code was set. Look for any history of previous codes, as well. Any fuel-trim related issues will also affect the performance of the cat converter.


Step 5


Check the OBDII Readiness Indicators to ensure all have been run to completion. If you have cleared some of the codes recently, some details of your engine or other components may read as incomplete. Thoroughly check all the scan data and if you find any deviation from the optimal readings, look into the problem and get it fixed.


Step 6


Check the Short Term Fuel Trim (STFT) and Long Term Fuel Trim (LTFT) data. The STFT indicates problems in the current fuel delivery and ignition processes, whereas the LTFT displays the fuel trim history. The latter can help you find whether your vehicle had ever run under rich or lean conditions.


While this page has focused on the procedure to diagnose a bad catalytic converter, knowing the causes and symptoms of cat converter failure can aid you in identifying problems earlier. This will ensure that your converter is diagnosed as soon as it starts showing symptoms of wearing out. To cater to the technical needs of our customers, our auto experts have written the article in the following link, that includes various aspects of converters such as their functionality and causes and symptoms of failure: Basic Knowledge About Catalytic Converters


Buying catalytic converters can be a bit of a tricky job as the regulations for catalytic converters vary with the area in which you live. Be sure to check the compliance standards of your specific area and get the right catalytic converter. If you are unsure of the correct match for your vehicle, talk to one of our specialists on our toll-free number or feel free to send us an e-mail. We are also here to help you out with any technical queries. Our US-based support team will make the purchase for your catalytic converter easy! stock a large selection of top-quality catalytic converters and other auto parts.


"How To" Home   |  BuyAutoParts Home