Notices
Tahoe & Suburban The power, space, and brutal towing ability make the Tahoe and its longer sibling, the Suburban, arguably the best full size SUV's on the market today.

2013 Chevrolet Suburban
Platform: GMT 400, 800, 900

Persistant P420 Code Will Not Clear After Cat Replacement

Old July 20th, 2018, 1:21 PM
  #1  
CF Beginner
Thread Starter
 
Join Date: Aug 2016
Posts: 5
Likes: 0
Received 0 Likes on 0 Posts
Default Persistant P420 Code Will Not Clear After Cat Replacement

I have a 2007 Suburban 1500 LTZ with the 5.3L V8 and Active Fuel Management. I have owned it for the last 5 years and since 107,000 miles. It currently has about 173,000 miles. Earlier this year, I got a check engine light with a P420 code. We replaced the cat with an aftermarket Eastern Catalytic converter. The check engine light persisted and then had a P430 and the O2 sensor codes. Had my my mechanic replace both upstream and downstream O2's on bank 1 and he felt we had a bad cat so he replaced the cat with another aftermarket unit that he sourced (different brand). Cleared the codes and the light stayed out for about 4-5 days and came back with just a P420. We checked for the ground wire to the cylinder heads per a TSB we found but are at a loss for what to do next. The engine is performing fine. The fuel trip and O2 values look good with my mechanics scan tool. No other fault codes are present that we can see besides the P420.

Any advice, suggestions, or ideas for us to check or look at would be helpful. The vehicle is running fine and I'd hate to think I just paid for two catalytic converters and neither fixed the issue.

Thank you.

Link
whfh99 is offline  
Old July 20th, 2018, 2:19 PM
  #2  
CF Addict
 
oldchevy's Avatar
 
Join Date: Apr 2012
Location: Miami, FL.
Posts: 3,603
Likes: 0
Received 2 Likes on 2 Posts
Default

Look for possible exhaust leaks and damaged wires to the O2 sensors.
oldchevy is offline  
Old July 20th, 2018, 2:52 PM
  #3  
CF Beginner
Thread Starter
 
Join Date: Aug 2016
Posts: 5
Likes: 0
Received 0 Likes on 0 Posts
Default

Those exhaust leaks would have to be upstream of the cats, right? And same with the O2 sensors, P420 is bank 1 (drivers side) and P430 is bank 2, correct? Just trying to narrow things down.
whfh99 is offline  
Old July 20th, 2018, 3:09 PM
  #4  
CF Monarch
 
kevinkpk's Avatar
 
Join Date: Jul 2011
Posts: 4,544
Likes: 0
Received 6 Likes on 5 Posts
Default

Since you replaced the cat's, I'd suggest looking at a leak at that point.
kevinkpk is offline  
Old July 21st, 2018, 7:24 AM
  #5  
CF Beginner
Thread Starter
 
Join Date: Aug 2016
Posts: 5
Likes: 0
Received 0 Likes on 0 Posts
Default

I don't see any leaks. I used a scan tool to monitor the O2 sensor live values for bank 1 and 2 this morning in my driveway. About 10 minutes after startup, the downstream 02 on bank 1 started to have voltage swings and started to look more like the chart pattern of the upstream sensor (Bank 1, Sensor 1). It leveled out again after a few minutes and the check engine light did not come on. However, I wonder if after a few drive cycles of this, it is enough to trigger the check engine light.

What would cause this behavior? Both Bank 1 O2 sensors were replaced in the last month.

Link
whfh99 is offline  
Old July 21st, 2018, 7:50 AM
  #6  
CF Addict
 
oldchevy's Avatar
 
Join Date: Apr 2012
Location: Miami, FL.
Posts: 3,603
Likes: 0
Received 2 Likes on 2 Posts
Default

Did you use cheap off brand O2 sensors?
oldchevy is offline  
Old July 21st, 2018, 8:00 AM
  #7  
CF Beginner
Thread Starter
 
Join Date: Aug 2016
Posts: 5
Likes: 0
Received 0 Likes on 0 Posts
Default

Probably, yes. I used DENSO O2 sensors from RockAuto.com bought back in May of this year. AC DELCO only?
whfh99 is offline  
Old April 5th, 2019, 5:11 AM
  #8  
CF Beginner
 
Join Date: Apr 2019
Posts: 7
Likes: 0
Received 0 Likes on 0 Posts
Default

Did this ever get resolved?
NYJOE is offline  
Old April 5th, 2019, 7:56 AM
  #9  
CF Beginner
 
Join Date: May 2018
Posts: 12
Likes: 0
Received 0 Likes on 0 Posts
Default

Originally Posted by whfh99 View Post
I have a 2007 Suburban 1500 LTZ with the 5.3L V8 and Active Fuel Management. I have owned it for the last 5 years and since 107,000 miles. It currently has about 173,000 miles. Earlier this year, I got a check engine light with a P420 code. We replaced the cat with an aftermarket Eastern Catalytic converter. The check engine light persisted and then had a P430 and the O2 sensor codes. Had my my mechanic replace both upstream and downstream O2's on bank 1 and he felt we had a bad cat so he replaced the cat with another aftermarket unit that he sourced (different brand). Cleared the codes and the light stayed out for about 4-5 days and came back with just a P420. We checked for the ground wire to the cylinder heads per a TSB we found but are at a loss for what to do next. The engine is performing fine. The fuel trip and O2 values look good with my mechanics scan tool. No other fault codes are present that we can see besides the P420.

Any advice, suggestions, or ideas for us to check or look at would be helpful. The vehicle is running fine and I'd hate to think I just paid for two catalytic converters and neither fixed the issue.

To find out about 02 sensors click here

Thank you.

Link
Hi.

There are several things that could cause this:
- exhaust leaks upstream of cat
- engine overfuling or burning oil
- poor quality 02 sensor.

If possible, try swaping out driver and passanger side o2 sensors. If you get P0430 after that, than it is a sensor problem.
Hope it helps.
harveyspecter is offline  

Thread Tools
Search this Thread

Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service

© 2019 MH Sub I, LLC dba Internet Brands

We are a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for us to earn fees by linking to Amazon.com and affiliated sites.
 
  • Ask a Question
    Get answers from community experts
Question Title:
Description:
Your question will be posted in: