Q: Can't pass emissions.

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My car's Check Engine light comes on and a cannot pass an emissions test. I had it diagnosed and it said the catalyst efficiency was below threshold in bank 2. The mechanic said the probable causes were a leak in the exhaust before the converter, a faulty heated oxygen sensor in bank 2, a rich fuel to air ratio, or a faulty catalytic converter.

The system should be scanned and the 02 sensors checked when the system is enriched to see if the sensors respond correctly. You could just have a defective sensor or a convertor that is bad. Only these tests can determine which one is the cause.

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