This Diagnostic Trouble Code (DTC P0420) relates to the efficiency of the catalytic converter on Bank 1. Bank 2 Code is a P0430. This stored Diagnostic Trouble Code (DTC P0420) is not definitive enough to just replace the parts based upon its’ indication.
Catalytic Converters are NOT wear out type parts and as such one that has failed should be highly suspect as to what caused it and more so IF it is truly bad. Otherwise if you simply replace the converter, send the vehicle out…the odds on you misdiagnosing the problem or failing to correct the real problem just went straight up. You can just about be sure that you will get a recheck on this vehicle.
According to several states that have emission testing programs in place, emission failures are down y/y. Currently the emissions test failures average about 9% of the vehicles tested. Of that 9%, 1 in 5 (20%) vehicles fails the retest. None of the states have data separated to show what the retest failure rate of the DTC P0420 is, but many state administrators state emphatically that the number one complaint of motorists references the P0420.
Let’s discuss Catalytic Converter construction from a very simplistic point of view!
Catalytic Converters are designed internally like a “honey comb”, the reason for this is it increases the available area for the reduction of pollutants. Each piece of the “honey comb” is coated with a very thin coating of precious metals that performs its’ function. Any coating like excess fuel, coolant, oil, etc reduces the converters capability and thus causes its failure. Even excessive carbon can stop its function or stop it up entirely.
Contaminants are such a problem for catalytic converters that the state of California has added an opacity test to their emissions testing.
Excessive heat is also a problem and can literally melt the converter internally.
To perform this job correctly you should look at the items that could have caused the reported DTC. Even simple things like an exhaust leak between the pre-catalyst and post catalyst sensors. A loose post catalyst sensor can cause it. Nothing should be overlooked as catalytic converters are far too expensive to install one when it is not needed, you need to go to basics and check everything.
If you have a catalytic converter that has overheated (outer shell having a bluish color) look for the problems, like too much alcohol in the fuel, too lean a mixture from stopped up injectors, overheating engine, vacuum leaks, misfiring cylinders, etc
You should check for Technical Service Bulletins (TSB) including those that address the possible need to reprogram the Powertrain Control Module (PCM) that may relate to the Diagnostic Trouble Code (DTC P0420 or P0430). If it needs reprogrammed that can be performed with J2534 tools such as ours.
A Scan Tool such as our 2x80 series scan tool with a good software package can be used to view the data from the Powertrain Control Module (PCM) to help with your diagnosis.
IF you are convinced that a new catalytic converter is needed, do your customer and yourself a favor and replace the pre-catalyst Oxygen Sensors (HO2S) as a precautionary measure.
Fix It Right The First Time!
Fortunately, everything you need everything you need to fix it right the first time is right here!
To access the sensor and data from your Engine Controller (PCM) you will need:
Professional Quality Scan Tool such as our 2X80S Scan Tool series.
If you understand how the systems were designed to work and how to test them, great! Otherwise you will need factory product service training manuals that will teach you and guide you through the diagnostic phase.
You might also need the manufacturer factory service manuals and data systems that provide specifications and details relative to your specific model.
Or aftermarket data systems such as All Data, Mitchell On Demand, Auto Data, Bosch, and others.
Everything is available here for you as a single source for all your needs. The aftermarket data systems are available in our members only area by direct shipment from the distributor at great pricing.