Persistant P420 Code Will Not Clear After Cat Replacement
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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.
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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
Thread Starter
CF Beginner
Joined: Aug 2016
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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.
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What would cause this behavior? Both Bank 1 O2 sensors were replaced in the last month.
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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
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
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.
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Joined: Apr 2022
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Frustrated
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
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