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Car seems to drive fine maybe underpower a little. Flashing wrenches and flashing D. Pulled code and p0422? Main Catalyst Efficiency Below Threshold Bank 1? Proper steps to determine problem? Any help would be appreciated.
 

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Your car has a catalytic converter that gets very hot and is designed to burn off fuel and gasses that make it through your car’s engine without being consumed. This reduces the amount of pollution coming out your car’s tailpipe.

Before and after the catalytic converter are oxygen sensors. The one before the converter (upstream) takes a measurement of these gasses prior to being burned in the converter. If you look at the signals from the upstream sensor, they should have large fluctuations depending on engine factors like speed, temperature, etc.

The sensor after the catalytic converter (downstream) should read the gasses after being burned, so if the converter is doing it’s job efficiency, the signals from the downstream sensor should be relatively stable with much smaller fluctuations. Both signals are fed into the car’s computer and if either is outside the specifications, a trouble code is generated.

Oxygen sensors have heaters in them to help them get to the correct operating temperature quickly. In many cases, the these heating coils go bad, or the circuits inside the sensors become faulty and the the error codes are indicating that the problem is with the oxygen sensor rather than the catalytic converter itself. Sensor failures are often easy to troubleshoot because the signals will be wonky (for example: 0 volts, .015 volts continuously, 12 volts continuously, etc.). But if the sensors are behaving ok, the catalytic converter may be faulty.

Using an infrared non-contact thermometer, it’s possible to read the temperature at the entry and exit of the catalytic converter. The exit temperature should be MUCH hotter than the inlet temperature, something in the range of 200-300°F hotter at the outlet than the inlet. If the temperature difference is small, you may be looking at a bad catalytic converter.

I hope this helps!
 
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