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Daryl
Daryl, Shop Owner, Master Mechanic
Category: Cadillac
Satisfied Customers: 12399
Experience:  28 years experience, Master Mechanic
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Cadillac STS: P0420 bank1 cat problem

Customer Question

P0420 bank1 cat problem
Submitted: 11 months ago.
Category: Cadillac
Expert:  Daryl replied 11 months ago.
Hello and thank you for trusting me with your question. My name is XXXXX XXXXX I will do my best to help you with your problem. With that code the shop you are referring to is correct, the cause is typically the Cat. The other 2% that code is usually caused by the oxygen sensors. Let me know if you have more questions on this I am always willing to help, Thanks.
Customer: replied 11 months ago.

I intend on doing this repair myself so the guidance I need is with the replacement of the cat. I understand it is on the passenger side and located as the lower cat. That is to say that it is not the pre cat but rather follows the exhaust to about the middle of the car. Can you help me with this?
Expert:  Daryl replied 11 months ago.
I just looked at a diagram for this exhaust system and it is only showing a right and left Cat, they just bolt on the upper and lower and there is a oxygen sensor that needs to be removed so I really am not sure what kind of help you are looking for?
Customer: replied 11 months ago.

I was looking for the diagram because I haven't been under the car yet. Also I was looking for you to verify that it is the passenger side for me based on the code. I would also be looking for a replacement cat so a part number would help me. Can you help me with these things and any tips on replacing the part like special tools needed or heat applied for removal?

Expert:  Daryl replied 11 months ago.

Yes that Cat is the passenger side, more than likely you will need some heat but in some cases you get lucky. This is a pretty tight job as in all the parts are in tight quarters, you are going to need a set of sockets and long extensions and wobbles to get in tight angles. Below is a diagram,

 

Expert:  Daryl replied 11 months ago.

It appears the diagram is not working, give me a minute.

 

Customer: replied 11 months ago.

OK I got it through the link. It looks pretty simple to do. Should I replace both or just the one they said is not good?

Expert:  Daryl replied 11 months ago.
I would just do the one, the other one may last the life of the car but you never know for sure so maybe down the road in a few years it may need replacing.
Customer: replied 11 months ago.

Ok thanks. How about a part number for the cat replacement? Will I need to purchase anything other than the cat like gaskets or lubricant for the threads on the O2 sensors?

Expert:  Daryl replied 11 months ago.
Are you thinking you are going to use after market parts or factory/dealer parts?
Customer: replied 11 months ago.

That was my next question. I would like to use the dealer part but I drive a lot and this car has 221900 miles on it. If aftermarket performance is ok to use than I would go that way to save the money. A suggestion of an aftermarket part would be helpful unless you think all aftermarkets are relatively equal.

Expert:  Daryl replied 11 months ago.
I personally would stick with the factory part for this the after market is kind of a toss up to weather or not the performance will be good enough, if it is not the check engine light will come back on. I can not get part numbers for dealer parts at this time of the day but if you take your VIN number with you the dealer will not have a hard time getting you the part you need. As for gaskets I believe that you need one on the top but the bottom you do not need any, these are cone type fittings, I usually put a anti seize on the threads of the oxygen sensors, just a little.
Daryl, Shop Owner, Master Mechanic
Category: Cadillac
Satisfied Customers: 12399
Experience: 28 years experience, Master Mechanic
Daryl and 4 other Cadillac Specialists are ready to help you
Customer: replied 11 months ago.

Daryl, can you clarify the location of this cat again for me. I once replaced a cat on the drivers side in my driveway on my back that was a Bear. If I remember right, I removed a heat shield then discovered the cat reached the manifold and was not easy to maneuver around in these tight spots. Is this passengers cat in the same location just on the passengers side or is it another destination of cats further down the exhaust system toward the back of the car? I was thinking it is around the middle of the car and second to one closest to the manifold? Not opposite of the one i had replaced a year ago.

Expert:  Daryl replied 11 months ago.
The one closest to the manifold is the one that would be bad on the passenger side, there is no other one further down the exhaust I believe what you may be referring to is a resonator its a kind of a pre-muffler to make the system more quite.
Customer: replied 11 months ago.

Thanks I was thinking that the resonator was what I needed to change based on the mechanics description. So now I know that this job is not as simple as a previously stated. However, I did do the drivers side myself last year. Do you think the passengers side will be more difficult for me to do? Also I have been looking online for replacement cats and came across re-certified OEM cats. What do you think about these. I have never heard of these before.

Expert:  Daryl replied 11 months ago.
I have never heard of the re-certified cats either, I think I would pass on that. I would expect the drivers side and the passenger side to be about the same as far as difficulty.

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