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96 1.0 with P0420 Code

05-17-2010, 11:14 AM
First of all, a big thanks to all you fellow Geo enthusiasts. I have read through many posts and find them all to be very helpful, especially to my pocketbook.

I have searched through all the posts with P0420 in them. The general consensus is that the Catalytic Converter is bad.

I have a 96 1.0 with about 110K miles. I have recently changed the oil, oil filter,fuel filter, pcv, and spark plugs. It does burn a little oil and I am sure in the future I am going to have to attempt to rebuild or replace the motor, but right now it purrs like a kitten, exept that the service engine soon light is on and the code is P0420 Catalyst System Efficency Below Threshold. (and saftey/emmissions is due in 2 weeks)

I read the codes with a TechII scan tool (borrowed from a friend) and ran it through a diagnostic where I watched the O2 sensor voltages as the engine warmed up. O2 #1 (pre Cat?) fluctuated while O2#2 stayed steady.

One of the threads that I read questioned whether or not a motor burning oil could foul the O2 sensor with oil. If the voltage readings appeared to be normal would it be safe to say that the O2 sensors are good but the Cat has seen better days and its time for a new one?

The Catalytic Converters that I have seen online look like they just bolt in place (if you can get the rusty bolts off). Would it be cheaper to have a muffler shop replace the Cat with a universal fit ( I have no welding skills or welding connections) or buy a direct fit online and attempt it myself?

Am I headed in the right direction? With gas prices starting to climb I would not be opposed to spending the money (to keep my fuel sipper going) for both a Catalytic Converter and O2 sensors, but there is no sense in wasting money if I don't have to.

Thanks in advance for any help you can offer.

05-17-2010, 02:07 PM

that's a good read... did you also reset the car's computer/clear the code and see if the same code returns?

if you can see under and if it's bolted on, it's easier to get a bolt-on replacement; i just cut off the rusted bolts and bolt it on...

05-17-2010, 02:26 PM
Thanks for the link, it is good information. I actually read that before I posted as I was researching this code.

I did reset the code and the light came back on in a couple of days.

I guess my concern with replacing the Cat is that from what I have read, a bad Cat will either cause the engine to run poorly, or the exhaust will have a rotten egg odor. My motor starts right up and idles smoothly. There is no noticible reduction in power or performance and I havent noticed any egg odors from the exhaust.

The pics of bolt on Cats look easy enough to replace if the bolts arent too rusty. That would be the way to go since I called the muffler shop and they want $229 to install a Cat, not including O2 sensors which I am sure they will tell me need to be replaced also.

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