Engine code 420


Asked by Jan 15, 2015 at 12:36 PM about the 2007 Pontiac G6

Question type: Maintenance & Repair

My check engine light has been on for a couple of months.  I had all o2 sensors, 2 selinoids, the catalytic converter and some type of timing manifold replaced and I am still getting the 420 code.  The mechanic has double checked everything and can't figure it out what else could it be?

4 Answers


Did they check for gasket leaks? I did the gaskets on my intake and was throwing those cat codes until I went back and did it right.


I'm not sure they have the car now and said they are going to check it to see if it is burning oil, is that the same thing as a gasket leak?


Take the positive cable off battery and leave of for about 10 15 mins put back on should solve problem


Yep. Aside from doing the battery thing , and to be clear I am not a mechanic, I've also read that a leaky valve cover gasket can present issues but not sure if it'll throw those codes because of it.

Your Answer

Add photo

Related Questions


Looking for a Used G6 in your area?

CarGurus has 5,673 nationwide G6 listings starting at $999.


Search Pontiac G6 Questions

Pontiac G6 Experts

#1 dandyoun
Reputation 570
#2 Andy Huhn
Andy Huhn
Reputation 520
#3 gmard1
Reputation 490
View All

Related Models For Sale

Used Pontiac G8"
19 Great Deals out of 463 listings starting at $5,300
Used Pontiac Grand Prix"
30 Great Deals out of 4,397 listings starting at $1,972
Used Chevrolet Malibu"
1,195 Great Deals out of 72,633 listings starting at $695
Used Chevrolet Impala"
994 Great Deals out of 35,760 listings starting at $700
Used Honda Accord"
1,344 Great Deals out of 77,641 listings starting at $1,395
Used Ford Mustang"
737 Great Deals out of 41,260 listings starting at $900
Used Nissan Altima"
1,452 Great Deals out of 87,459 listings starting at $1,195
Used Pontiac G5"
9 Great Deals out of 634 listings starting at $2,499
Used Dodge Charger"
656 Great Deals out of 29,890 listings starting at $1,995
Used Chevrolet Cobalt"
103 Great Deals out of 5,569 listings starting at $950
Used Honda Civic"
1,190 Great Deals out of 58,109 listings starting at $1,300
Used Ford Fusion"
1,463 Great Deals out of 79,123 listings starting at $1,450
Used Toyota Camry"
1,666 Great Deals out of 98,110 listings starting at $895

Used Cars For Sale

2010 Pontiac G6 For Sale
11 Great Deals out of 273 listings starting at $3,921
2009 Pontiac G6 For Sale
23 Great Deals out of 940 listings starting at $999
2008 Pontiac G6 For Sale
47 Great Deals out of 1,381 listings starting at $1,900
2007 Pontiac G6 For Sale
56 Great Deals out of 1,494 listings starting at $1,599
2006 Pontiac G6 For Sale
10 Great Deals out of 1,206 listings starting at $2,900