DTC P0420 Catalyst System Low Efficiency

[DominusEtDeusNatus]

A while back I got a SES light :D TC P0420 Catalyst System Low Efficiency. So I'm thinking either the cat or the after the cat O2 sensor is malfunctioning. I got an O2 SIM. SES light went away. It didn't come back for over 2 months. Now it's back again. Could this someone be my pre cat O2s? I really don't see how when it mentiones the cat. Anyone ever fix this code?

[rockotman]

That code is typically caused by the post CAT 02 sensor. GM has had problems with getting "false alarms" due to the sensor, even when the sensor is good. Unless the vehicle is running bad, or not passing emmissions testing, I wouldn't get too upset about it.

How many miles are on the vehicle? If I'm not mistaken, isn't the manufacturer on the hook for any CAT related stuff up to 80K miles?

[TheBeast]

I'm getting that code right now. Its been on for like a week now, which is longer than usual... it needs to go away so I can sell the car! lol the person who buys it may not get it that the code is pretty much BS

[John_D.]

Did you sim your pre and post, or just the post?

The pre is just a baseline reading to compare the post against, I believe. So the pre should be a live o2, and the post a sim. Otherwise they will both read the same, which will be bad.

Or did the sim work loose from the connector at all...?

That's all I can think of.
(unless the pre went bad to the point that now the post sim reading looks bad compared to it...)

[DominusEtDeusNatus]

SIMs are for post cat sensors. I'm thinking maybe the SIM went bad or got disconnected. I'll check it today.

[TheBlackSwordsMan]

if its the precat sensors you would know it because your car would be eating gas like a mofo