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Code 420 is on .cad is running very rough. I'm told cat is…

Customer Question
Code 420 is on...

Code 420 is on .cad is running very rough. I'm told cat is bad thinking of diy project

Mechanic's Assistant: Just to clarify, what's the exact code? And have you tried to reset it?

[t now reads po307. it was reading po420 before

Mechanic's Assistant: What is the model/year of your Cadillac?

2004 4.6 v8 srx

Mechanic's Assistant: What year is your SRX?

2004

Mechanic's Assistant: Are you fixing your SRX yourself? What have you tried so far?

I was going to depending on how involved it is

Submitted: 3 months ago.Category: Cadillac
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Answered in 2 minutes by:
3/21/2018
Cadillac Mechanic: Ron Z., - Cadillac Tech - replied 3 months ago
Ron Z.
Ron Z., - Cadillac Tech -
Category: Cadillac
Satisfied Customers: 19,937
Experience: 18+yrs experience. State Inspector and Cadillac Diagnostics
Verified

Hi! Welcome to JustAnswer. Thanks for coming! I'm Ron and I'll be working with you on your question today. Please give me a moment to review your question and type out my reply. Sit tight one minute... I'll be right back!

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Cadillac Mechanic: Ron Z., - Cadillac Tech - replied 3 months ago

Thanks for holding!

When the engine has a cylinder misfire (P0307) this will quickly harm the catalytic converter. So, strong chance that the P0420 is being set because the converter is being affected by the cylinder #7 misfire. As long as the vehicle hasn't been run very long with the misfire present, more times than not, the converter can usually be saved. So, my advice would be to solve the P0307, clear the codes and if the P0420 returns... then replace the converter.

With that said... there are a few different things that can cause a single-cylinder misfire. This can be a worn spark plug, a faulty ignition coil, a faulty injector, low cylinder compression, etc. More commonly here is the plug, coil or injector, so these are the best places to start. Remove the spark plug and inspect the body for any cracks and the diode for excessive wear. If there are any doubts, replace all the plugs. If the plugs check good, you can swap the ignition coil with another and see if the p-code follows (ie: P0307 is now P0305). If so, replacing the coil will solve the problem. If the coil checks ok, move onto the injector. With the engine running, unplug the electrical connector to the injector. The engine should respond. If not, the injector will need to be replaced. If all of these check ok, then deeper diagnostics will need to be done and ultimately, a cylinder compression test. Please be kind enough to leave a rating for our Q&A using the 'stars' at the top of the page or click 'Accept' when I have answered all your questions. A 5-star rating is very much appreciated! Rating or accepting my answer does not cost you extra.

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Cadillac Mechanic: Ron Z., - Cadillac Tech - replied 3 months ago

HI! I noticed this Q&A was still open and you did not leave a rating, so I wanted to check in and see if there was anything else I could do for you on this? Any other questions you had? If you have no further questions, Please be kind enough to leave a rating for our Q&A using the 'stars' at the top of the page.

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