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Old 04-06-2006, 11:58 AM   #1
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Default Great, another SES Light, P0420

Alright, looking for some advice. After recently fixing an EVAP leak and resetting the SES, I had it pop on again yesterday. I scanned it (glad I bought the scan tool now...thought I'd never use it, haha), and got Code P0420. My car is a 2003 SSEi with about 104K on it (I drive A LOT).

From searching around the forums here, It looks like this is caused by either a bad Catalytic Converter, or O2 sensor. It seems, from what I'm reading, that the Cat is the most likely culprit. This seems like a "possible" DIY jobber.

Now, for the question- I am not an experienced welder, and this car has the original Cat in it, so I'm guessing it will just be a "bolt-on" application. Is there a Cat on the market that will be a direct replacement/fit for my car? I would consider going with a high-flow cat, especially since they seem cheaper than OEM which are ridiculously high priced.

$60 for the part on EBay seemed like a great price, but that looks like it'* for a Universal Fit Cat, and may require welding. If I try to cut and weld...well, it would be bad. In pinch, I may be able to find someone to help with the welding, but would prefer to rely on my own skills (nun chuck skills, bow-hunting skills, computer hacking skills, j/k)

Thanks in advance for any advice. You guys are big money savers!
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Old 04-06-2006, 12:25 PM   #2
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js, not to stop you from buying a hi-flow cat, but consider a few simpler tests first to make sure that is your problem.

Suggestions from FSM are:

Checks connections at the PCM and your wiring harness for backed out terminals, broken terminal locks, damaged terminals, and bad or worn wires. This especially includes the wiring on both 02 sensors.

If everything looks OK, then hook up your scan tool and watch the screen while moving connectors and wires that are related to the O2 sensors. A change in display will indicate a problem area.

Then monitor O2 sensor activity while in Park. If the activity level of both sensors is about equal, then there is a problem. Your 2nd O2 should show much less activity.

Then, if problem is still indicated, visually inspect the cat for dents, discoloration caused by severe temps, holes, or internal rattling. Also inspect exhaust downpipe and surrounding pices for damage.

Then, if you determine you need a new cat, there should be a direct fit one for your car available. Try carsound and other performance parts places online. The universal fit one will work, but as you said, why do that if you can get a direct fit?
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Old 04-06-2006, 12:39 PM   #3
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Awesome,
Thanks Lash. I plan on jacking the car up and running through all the tests this weekend. Like you said, it makes no sense if it'* just a loose or bad wire, or a bad O2 Sensor. I will use the multimeter to check the voltage at each O2 also.

My scan tool is really basic, I think. It doesn't give me some of the functionality that I sometimes need. Sucks because I spent a little more on one that was CAN-OBD compliant, thinking it was a better tool. Maybe I was wrong.

I just wanted to get some advice on the cats since, if it is bad, I want to get it replaced the following weekend, and will want to order it ASAP after doing the inspections.

Thanks again!
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Old 04-06-2006, 07:50 PM   #4
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Catalytic converter should last many years.
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