If the engine computer has a p0430, then the odds are that the converter is bad. The engine computer looks at the front oxygen sensor and compares it with the rear oxygen sensor for each converter. This is how the computer knows if the catalytic converters are working. A few things can cause a false code such as a exhaust leak, or a oxygen sensor that is covered with mud.
The engine computer is very good at testing the converter, GM does not want to replace converters under warranty so they make sure the system works. I would check to make sure there are no exhaust leaks. Also it may be a good idea to clear the code and see if it comes back. Bad gas or a misfire can also cause this code to set.
The catalytic converters are covered under warranty for 8 years or 80k miles. If you are under this, they will replace it for free.
DTC P0420 or P0430
In order to maintain low emissions of hydrocarbons (HC), carbon monoxide (CO), and oxides of nitrogen (NOx), the engine controls system uses a 3-way catalytic converter (TWC). The catalyst within the TWC promotes a chemical reaction, which oxidizes the HC and CO that are present in the exhaust gas. This reaction converts these chemicals into harmless water vapor and carbon dioxide. The catalyst also reduces the NOx which converts into nitrogen. The powertrain control module (PCM) monitors this process using heated oxygen sensor (HO2S) bank 1 sensor 2, which is located in the exhaust stream past the TWC. The HO2S bank 1 sensor 2 produces an output signal which indicates the oxygen storage capacity of the catalyst. This determines the catalysts ability to effectively convert the exhaust emissions. If the catalyst is functioning correctly, the bank 1 of the HO2S 2 signal will be far less active than the signal that is produced by bank 1 of the HO2S 1. This indicates that the TWC oxygen storage capacity is below an acceptable threshold.
The PCM performs this diagnostic test at idle. When the conditions for running this DTC are met, the following occurs:
- The PCM captures the current rear HO2S rich-to-lean status.
- The air-to-fuel ratio transitions from rich to lean or from lean to rich, depending on the captured rear HO2S rich-to-lean status.
- The air-to-fuel ratio transitions a second time opposite the first air-to-fuel ratio transition.
- The PCM captures the response time of the front and the rear HO2S when the air-to-fuel ratio transitions occur. The HO2S response time goes from less than 300 mV to more than 600 mV, and from more than 600 mV to less than 300 mV.
- The PCM measures the time necessary for the rear HO2S voltage to cross a reference rich-to-lean threshold, minus the time necessary for the front HO2S voltage to cross the same rich-to-lean threshold. The difference between the front HO2S time and the rear HO2S time is the oxygen storage capacity of the catalyst. This DTC sets if the time exceeds a predetermined threshold.