P0420 Cat Inefficiency

[HighRollerRich]

I'm throwing a P0420 for Catalytic inefficiency (bank 1)

-is that actually a clogged cat or is it one of those codes you have to start digging to find the problem??

 

[Mike]

Probably a dead cat or sensor.

 

[HighRollerRich]

will it hurt anything else driving around with the cat "clogged" and SES light on?

 

[Mike]

I don't think the post - cat sensors affect the performance of the engine, just the pre-cat sensors. You will not pass inspection in my state however.

 

[Ginger]

if the cat is clogged it is going to run really ******, and basically in limp mode,

i had a reading like that on my truck, i had justin tune out the post cat o2 sensors, and hollowed my cats out

 

[Butch]

my left bank cat went out so I pulled both of them out, a clogged cat will also cause your motor to overheat while towing. It happened to us with a 98 S10 Blazer 4.3L/4L60e.

 

[Hodges87]

I would swap your rear 02 sensor sides and if it still shows up then you have a bad cat. I had the same code and I had a bad cat, so I bought the magna-flow cats for my 97 Z71

 

[GMCzar]

I did a little research and this is what I found:

Causes
- Leaded fuel was used where unleaded was called for
- An oxygen sensor is not reading (functioning) properly
- The engine coolant temperature sensor is not working properly
- Damaged or leaking exhaust manifold / catalytic converter / exhaust pipe
- Retarded spark timing
- The oxygen sensors in front and behind the converter are reporting too similar of readings

Possible Solutions
- Check for exhaust leaks at the manifold, pipes, catalytic converter. Repair as required.
- Use a scope to diagnose the oxygen sensor operation (Tip: The oxygen sensor in front of the catalytic converter normally has a fluctuating waveform. The waveform of the sensor behind the converter should be more steady).
- Inspect the downstream heated oxygen sensor (HO2), replace if necessary
- Replace the catalytic converter

Hope this helps.