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Well, a broken exhaust stud could eventually allow it to develop a gasket leak. I'd fix the stud anyway and then clear the codes and recheck them.
"P0420 Catalyst System Low Efficiency" - this can be either a failed catcon or, more likely, a failed downstream O2 sensor.
How does it run?
"P0420 Catalyst System Low Efficiency" - this can be either a failed catcon or, more likely, a failed downstream O2 sensor.
How does it run?