Catalytic Converter 101 Page 2

Most people will automatically assume that the catalytic converter is the reason that the smog test has failed, and usually that is correct although there are other things that could affect the tailpipe emissions.  If the evaluation of your vehicle does indicate that the catalytic converter is at fault, then it should be determined why the converter is not working correctly.  Has the engine not been properly tuned?  Has the engine been using oil or coolant that could be contaminating the internals of the converter?  Is there any indication that the converter has been over heated or damaged from hitting something?   Is there a rattling sound coming from the converter area?  

 

The first step should be to have a qualified technician check the vehicle. The technician will perform various tests to diagnose why the converter has failed and then correct the problem before a new converter is installed and possibly damaged from the same reason.  If the car/truck is new enough, the onboard computer system (known as On Board Diagnostics level 2 or OBDII) may have turned on the Check Engine light which indicates that the OBDII tests have noted some problem and have set a code within the computer to alert you that a problem has occurred that will damage the car and possibly has already damaged the converter.   The technician can connect a hand held computer that will allow him to “read the codes” and identify what problems the on board tests have identified.  Once that is done and the problems corrected, if the tech has determined that the converter has been damaged, then is the time to look into replacing the converter.

 

In the state of California, there are strict requirements as to what parts can be used to replace defective catalytic converters.  Prior to the 1995 model year, it is most likely that there will be an aftermarket part that can replace the original catalytic converter, and because of the age of the vehicle, usually it is very difficult to find a new, original catalytic converter so that necessitates the use of an aftermarket part.  Each vehicle has a state approved part that is based on the model year, engine size and physical placement of the converter, so you cannot just buy the cheapest one you can find and have it installed because, at some point during the smog test, the smog technician is required to verify that any replacement parts are the correct part number for that application.  

 

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