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2006 Cadillac DTS luxury ll, 2007 Cadillac DTS performance
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Discussion Starter #1
After about 3 months of owning my DTS the check engine light came on and the code was p0420 and we replaced the cat converter and that didn’t help and then the front upstream o2 sensor and it still didn’t help what could be my problem
 

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2007 DTS LuxII, 1969 El Camino SS396, 2008 GMC 2500HD Crew Cab 4x4,
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88 Posts
You can go to a quality auto parts store (see if they can scan it for you) that has a GOOD scan tool to drill down to some detail to provide you with more information to assist with the diagnosing of the issue. Seems to be I've seen this code on my GMC 2500HD and ended up replacing bank 1 sensor 2 (downstream) O2 sensor. I replaced it and haven't seen a check engine light on it since then.
 

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2002 STS; 2006 DTS
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5 Posts
After about 3 months of owning my DTS the check engine light came on and the code was p0420 and we replaced the cat converter and that didn’t help and then the front upstream o2 sensor and it still didn’t help what could be my problem
did you get the problem worked out... I am in the same boat.
 

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2006 Cadillac DTS luxury ll, 2007 Cadillac DTS performance
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5 Posts
Discussion Starter #4
did you get the problem worked out... I am in the same boat.
I had tried everything and then Talked to some family and they told me to get a ECU and then I ordered one and took it to the dealership and had them program it to my car
 

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2006 DTS, 1996 STS - RIP
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297 Posts
We have a 2006 also and had that code, there is a very helpful GM tech (danog) on here
who, as I remember, said that the early ECU program (2006) was too sensitive as far as
the Cat goes. As I remember the first step for replacing the Cat at the dealer is to update
the firmware which I think they did on our car and the Cat also free of charge since we
were just under the time limit.

Here's the long story. Good news is that I believe they did do the ECU update since
the electrical problems seem to be mostly better:
 

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2006 Cadillac DTS luxury ll, 2007 Cadillac DTS performance
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5 Posts
Discussion Starter #9
After a lot of difficult with my dealer I have taken my car to another gm dealer nearby and it turns out that my Throttlebody has been staying slightly open and caused it to heat my o2 sensors and stop up my converter
 

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2006 Cadillac DTS
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62 Posts
I have a 06, had same problem, replaced with a cheapy o2 sensor, and code went away for say 6 months, and returned. I have not changed it again yet, but I bet once I change it to a oem one, will resolve the code.
 

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2006 Cadillac DTS luxury ll, 2007 Cadillac DTS performance
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Discussion Starter #11 (Edited)
I have a 06, had same problem, replaced with a cheapy o2 sensor, and code went away for say 6 months, and returned. I have not changed it again yet, but I bet once I change it to a oem one, will resolve the code.
At the dealer that has diagnosed my car they said that it’s not always a bad thing to use aftermarket things but that it’s hit or miss weather they will actually fix it and work
 
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