P0420 Code Emissions Problems

GaryFenza · #1 08-11-2008, 09:15 PM

on the way home today i got a P0420 code which supposeldy means a faulty cat converter, is there any home that it could just be a bad 02 sensor or a 02 sensor that is not working as required, i didnt notice any leaks at the cat conv. The service engine soon light is on steady not blinking, any ideas what i should do?

tblake · #2 08-12-2008, 12:59 AM

Buy a bolt in high flow downpipe and high flow cat converter from ZZP.

richtazz · #3 08-12-2008, 03:33 PM

P0420 is catalyst efficiency below threshhold. The PCM uses the MAP sensor vacuum signal to determine EGR efficiency, and the MAP sensor is located in the intake just above the PCV valve. Have you recently done any tune-up work including replacing the PCV valve? If so, and you didn't replace/reuse the small black o-ring on the PCV valve itself, the resulting vacuum leak will trip a P0420 code.

BNaylor · #4 08-12-2008, 04:10 PM

Quote:

Originally Posted by richtazz

P0420 is catalyst efficiency below threshhold. The PCM uses the MAP sensor vacuum signal to determine EGR efficiency, and the MAP sensor is located in the intake just above the PCV valve. Have you recently done any tune-up work including replacing the PCV valve? If so, and you didn't replace/reuse the small black o-ring on the PCV valve itself, the resulting vacuum leak will trip a P0420 code.

Didn't you mean P040X like P0401, P0402 which are EGR related DTCs Rich?

I agree with Tim the P0420 DTC is a bad CAT converter.

richtazz · #5 08-12-2008, 04:14 PM

I was just going to correct myself, had a brain fart moment there, sorry for the mistake. Got my p04xx codes confused,

BNaylor · #6 08-12-2008, 04:54 PM

Quote:

Originally Posted by richtazz

I was just going to correct myself, had a brain fart moment there, sorry for the mistake. Got my p04xx codes confused,

No problem Rich. I get those too. Comes with age for some reason.

.....

GaryFenza · #7 08-12-2008, 04:58 PM

i noticed the car runs fine though, i cant tell a difference in performace. I deleted the code and the service engine light has not returned and i drove about 75 miles today. the only thing a i can notice is the fumes from the car smell a little strong, but i also noticed that the motor was running VERY rich, couldnt that trip the P0420 code? Bad o2 sensor??

BNaylor · #8 08-12-2008, 05:08 PM

Do you have any exhaust systems leaks before the CAT converter?

Check the short term and long term fuel trim values with a full function odb-ii scan tool.

GaryFenza · #9 08-12-2008, 05:13 PM

the short term and long term fuel trims looked good. I didnt notice any leaks before the cat converter at all. I thought if it was a bad cat. i should deff. be noticing a drivability difference, but i cant notice anything.

jd-autotech · #10 08-12-2008, 05:27 PM

there is a recall free replacement through gm upto 100,000 miles hope you are under that but you need a converter to fix it and the code will reappear if you use an aftermarket. some times you can get away with aftermarket replacement if you clean the snot out of the maf

BNaylor · #11 08-12-2008, 05:32 PM

Quote:

Originally Posted by jd-autotech

there is a recall free replacement through gm upto 100,000 miles hope you are under that....

Are you sure? Last time I checked it only covers '01-'02 model Grand Prixs and other GM cars with the NA or SC engines. The CAT warranty was extended by GM to 10 years or 120K miles, whichever comes first. The info and letter from GM in which I received for my '01 Regal GS is posted at our Tips & Maintenance forum.

The OP has a 2003 model GT.

See link below.

http://www.automotiveforums.com/vbul...d.php?t=681283

BNaylor · #12 08-12-2008, 05:35 PM

Quote:

Originally Posted by GaryFenza

I thought if it was a bad cat. i should deff. be noticing a drivability difference, but i cant notice anything.

Not necessarily. You can just get the P0420 DTC with no driveability issues. You can waste your time or ours but get the CAT converter tested!

jd-autotech · #13 08-12-2008, 05:38 PM

certain 03 models are involved in the recall and yeah your right it is 10 years- 120,000

jd-autotech · #14 08-12-2008, 05:40 PM

you can have the pre converter o2 sensor removed have a back pressure tester installed and check for back pressure if anything more than 1 p.s.i. the converter is junk

tblake · #15 08-12-2008, 08:09 PM

So, if you smell gas and the car is running rich, lets figure out why so you dont burn up another cat converter.

What exactly are your long term fuel trim numbers?

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