Ok. so my 2001 ls is throwing a code. I own the actron OBD2 scanner from advance auto parts and the code that comes up is P0420. Reads "catalyst efficiency below threshold bank 1". The question here is...what the hell does that mean?? Im getting no funny driving feelings or sounds. Anybody got any bright ideas?

 

I have a bright idea- use this thing we call "logic" to figure it out. I'll give you a hint...the part that is having a problem is listed in the code description

 

I have no specific knowledge of this problem on Miatas, but based solely on the code description I would think that means it's sensing excess fuel downstream of the cat. Could be that the downstream o2 sensor needs replacing, at least that would seem more likely than the cat itself failing. The term "efficiency" implies some comparison of pre-cat and post-cat sensor readings so I suppose a faulty pre-cat sensor might also cause that code. (?) Maybe also check for exhaust leaks. It doesn't sound like a code that would come with any real driveability issues so you're probably okay to keep driving it.

 

Get two 18mm spark plug non foulers, drill out the insides so your downstream o2 sensor can thread in. Gut your cat. Thread in non-foulers and o2 sensor. Reset the ecu and forget about that ****.

edit: this will not work if the sensor is fucked.

 

thanx guys. I also googled the code and found for myself the cat is done. I just replaced both my o2's less than a month ago. I suppose its time to replace the cat.. anyone got a place to find a cheap bolt in??

 

After I use the scanner on a car. Thats exactly what I tell people to do.

 

The downstream o2 sensor is detecting excessive unprocessed gasses. The catalytic converter's efficiency is below it's minimum operational range. Thus the ECU throws an emissions-related code to let you know to replace the converter. Either find a OE mid-pipe or do the aforementioned anti-fouler trick.

 

If you just replaced you o2 sensors then I agree with you... the Cat is done, probably got polished off from the way it was running before you changed the sensors.

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