What is P0420 TWC System Low Efficiency?
TECH Fanatic
Joined: Nov 2001
Posts: 1,497
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From: Katy, TX
Re: What is P0420 TWC System Low Efficiency? Catalyst system Low effeciency
normally when there is a big shift in the pre catalytic converter o2 sensor, the post converter sensor is very slow to change.
If the computer senses the post converter sensor make a rapid change along with the pre converter sensor...it assumes the catalytic converter is bad , and throws the code.
if it is not sensed in three consectutive trips the dtc will go away, 40 consecutive trips it will be removed from the dtc history.
gm service manual in a run down says to inspect the catalytic converter, and exhaust system for damage, change converter if necessary, and inspect and change o2 sensor/wire if necessary. but they first recommend running several drive cycles, and seeing if the code clears.
hope that helps
normally when there is a big shift in the pre catalytic converter o2 sensor, the post converter sensor is very slow to change.
If the computer senses the post converter sensor make a rapid change along with the pre converter sensor...it assumes the catalytic converter is bad , and throws the code.
if it is not sensed in three consectutive trips the dtc will go away, 40 consecutive trips it will be removed from the dtc history.
gm service manual in a run down says to inspect the catalytic converter, and exhaust system for damage, change converter if necessary, and inspect and change o2 sensor/wire if necessary. but they first recommend running several drive cycles, and seeing if the code clears.
hope that helps
Re: What is P0420 TWC System Low Efficiency? Thanks alot for the info. I have a 3 year old high flow cat so that shouldn't be it. It's probably my 02 sensors as I'm hitting 100,000 miles soon. Is there anyway to check if they are going bad?
There is 4 of them total. Do I need to replace the 2 that are recommended to be replaced at 100,000miles or all 4? What's the recommended replacement of the other 2?
<small>[ April 21, 2002, 07:06 PM: Message edited by: Dom ]</small>
There is 4 of them total. Do I need to replace the 2 that are recommended to be replaced at 100,000miles or all 4? What's the recommended replacement of the other 2?
<small>[ April 21, 2002, 07:06 PM: Message edited by: Dom ]</small>
TECH Apprentice
Joined: Jan 2002
Posts: 364
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From: Princeton, IN
Re: What is P0420 TWC System Low Efficiency? I just had a run around with an o2. Do you have autotap? If so you are not getting any other codes? I was tripping po133 (slow o2) I would think if it where going bad you might get something like that. Also the heater could be bad. As I had to learn the hard way, at least on the 98's the two o2 sensors on bank1 s1 and bank1 s2 are the same (acdelco afs98) so you could move the o2 back and forth. You can do the same to the other bank. I don’t think the sensors them self are different (just the wire) if you move them around it might show it’s self as a different problem but follows the o2 it’s self. I would move mine around and started to trip different codes but it followed the o2 sensor. Maybe a leak in the exhaust could cause something like what you’re getting.
