What is P0420 TWC System Low Efficiency?

[DominusEtDeusNatus]

I got this code recently and don't know what to check or replace. Does anyone know what is it?

[Dojo2000]

"Catalyst system efficiency below threshold, left bank" - Haynes Repair Manual

something to do with your O2 sensors. do a search, someone had this problem recently. Hope this helps.

[img]graemlins/burnout.gif[/img]

[DominusEtDeusNatus]

I was thinking it might be the oxygen sensor. I have over 100,000 miles and it hasn't been replaced yet. Is there a difference in what brand I go with? Bosch or others?

[Dojo2000]

Don't know about different brands, not sure if it even makes a difference with something small like this(except quality probably effects life of sensor), BUT from what i've heard, Bosch are very good and have a price to match :D I think last time i checked it was ~$50 for one. :( and we have 4!

Now that i think about it, my car also has over 100K miles on it, and the SES light has been coming and going for a month or two. How did you pull that code, cause i need to find out why mine keeps getting set? It will turn off and on while i'm driving [img]graemlins/dunce.gif[/img] . Off the top of my head i thought it might be my IAT sensor because its been a lil abused.

[img]graemlins/burnout.gif[/img]

[ April 20, 2002: Message edited by: Dojo2000 ]</p>

[DominusEtDeusNatus]

I went to get price estimates at PepBoys and Autozone. Two of them say they need to be replaced at 100,000 and it's $60 at PepBoys(don't know brand) and $50 at Autozone for Bosch. These are the two before catalyst. The other two are $80 at Pepboys and $75 at Autozone.

I can't believe they are so expensive. Total would be $250-$280 if I wanted to replace all 4. I might just replace the two that need to be replaced at 100,000.

I had Keith autotap the code for me so that's how I know. It only showed up once though. I reset the PCM and haven't seen the code yet. I guess it's probably an early warning.

[DominusEtDeusNatus]

The ones in the left and right manifold are the ones that go bad after 100,000miles right? I don't want to replace the wrong ones since they're so expensive.

[Guardsman]

I would say the difference in the brand would be a difference in quality, as was mentioned before.
Dojo, Autozone has scanners that you can borrow, and use in their parking lot, and you can run it there. If you have a 98+ car, it plugs in by your right knee in the driver's seat.

[DominusEtDeusNatus]

Ok so which sensor do I need to buy?

AC Delco part # GM part # Description
AFS-17P 8990793 three wire, 4 hole connector
AFS-40 25108302 four wire, 4 hole connector, redundant signal ground
AFS-41 25108814 three wire, 3 hole connector
AFS-45 25132086 four wire, 4 hole connector, redundant signal ground
AFS-49 25132271 three wire, 3 hole connector
AFS-60 25132529 four wire, 4 hole connector, redundant signal ground
AFS-48 25132169 three wire, 4 hole connector
AFS-63 25132674 three wire, 4 hole connector
AFS-62 25132616 four wire, 4 hole connector, redundant signal ground
AFS-65 25132819 four wire, 4 hole connector, redundant signal ground
AFS-66 25132789 three wire, 3 hole connector
AFS-72 25133358 four wire, 4 hole connector, redundant signal ground
AFS-75 25312184 four wire, ???

I have to buy them in pairs right?

[P-nut-]

Here you go... P0420.pdf