When you have a code that says cat inefficiency (assuming this was your code) then all that is saying is that based on the o2 sensor data the PCM thinks the converter is not reducing the emissions enough.
So, this means it can be a faulty o2 sensor and this would be the more likely cause then both converters failing at the same time.
Here is a guide that will help with testing a converter:
Also, the best way to check the converters is to monitor the o2 sensor info. The most common cause of this is faulty upstream o2 sensors where it says the oxygen content is low and the downstream sensor is reading properly but they are higher than the upstream, so it assumes the converter is not reducing any emissions.
If you think about this, this is a clear sign the upstream o2 sensors are faulty because you cannot have higher fuel content after the converter then before it. O2 sensors do not detect fuel, only oxygen but when there is less oxygen, it is being offset by fuel so indirectly you are reading the fuel in the exhaust as well.
The only exception to this is if you have misfires that has damaged the o2 sensor and converters.
However, if you let us know what codes you have, we can attach the specific testing so that you can run through this and confirm what the issue is.
Please see the info attached below. Let us know if you have other questions. Thanks
Images (Click to enlarge)
Sunday, October 3rd, 2021 AT 2:50 PM