Scan Code 420--What Does It Mean?

[sefa01]

Just had a Maggie put on last month. Engine light came on recently. Had scan done at AutoZone and it showed Code 420. What does it mean and what should I do?

[v-ape]

CTS-V420 may know the answer....

[The Tony Show]

If I remember correctly, it's poor Catalyst efficiency. Either the tune is too lean and your cats are shot, or there's a problem with the rear O2 sensors not reading correctly.

Keep in mind that the above applies only IF P0420 is poor catalyst efficiency.

[zozmanCTS-V]

Originally Posted by The Tony Show

If I remember correctly, it's poor Catalyst efficiency. Either the tune is too lean and your cats are shot, or there's a problem with the rear O2 sensors not reading correctly.

Keep in mind that the above applies only IF P0420 is poor catalyst efficiency.

Correct---P0420 = Catalyst System Low Efficiency Bank 1.

[The Tony Show]

Awesome! What did I win?

[ZEUSROTTY]

your car is craving weed...

[1MEANV]

mine said that code once and it was becasue my cats were ****ed

they were blowen out and needed to be replaced

[heavymetals]

You could turn off the rear sensors.

[ewill3rd]

Do you have aftermarket cats too?

P0420 means the catalyst is not passing the self test, basically it is bad.
That is the left bank cat.

[stkshkr]

I get that code or PO421 about every three or four months with the Maggie and RT cats, I just clear it and continue on. Don't sweat it

[Rey]

Go to www.gearchatter.com. They have in-depth writeups of codes. They don't have a specific section for the CTS-V, but a Corvette of same vintage should be identical.
You may have a bad 02 sensor, and it is usually the front sensor that goes bad. What you can easily do is switch your front sensors - left to right and vice versa. One sign of an cat failure is the innards becoming loose. A little tapping on the cat may indicate loose innards.

[ewill3rd]

The O2 sensors must pass the PCM tests before the catalyst test can be run.
A very specific set of criteria must be met for a P0420 to set, which can't happen with bad O2 sensors.

One way a catalyst can fail is physically breaking, but I have seen physically broken (rattling) cats that would still pass the self test, and unbroken cats fail. The PCM test checks the catalyst for oxygen storage ability, if it cannot maintain proper levels the test fails.
That is pretty much it.

Most aftermarket catalysts do not seem to have the proper composition to make the factory diagnostics pass for the converters.
I can't tell you how many times I have seen people install aftermarket cats trying to "save money" (on emissions failures) only to have the check engine light come right on.
Some performance guys put high flow cats on and end up in the same boat.

From a technical standpoint, changing a cat with one that doesn't do the exact same job is a violation of federal emissions regulations and subject to some pretty stiff penalties.
Also reflashing the PCM to turn off the catalyst monitor is the same thing.
Not much to be afraid of in terms of enforcement, but if you are in an emissions testing area, get ready for a battle every time you need one done.

[2004 CTS-V]

I have the same code popping up: P0420. Is this definitely the catalytic convertor on the left side? What is the code for the right side?

Thanks.

[darkman]

See attached.

[ewill3rd]

Right bank is P0430.
P0420 is Bank 1 and P0430 is bank 2.

Depending on which bank is on which side depends of course on which one is left or right.
On the V bank 1 is the left (driver) bank.

High flow cats have a tendency to fail the OE diagnostic.
Since technically installing them is a violation of federal emissions law then tuning the ECM to turn those codes off shouldn't be much of a problem.
If it is a stock cat setting the code then coverage is 8 years and 80,000 miles for warranty replacement.