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Old 06-08-2021, 02:51 AM   #1
nj9000
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Default P0420 and smoke

'99 Saturn SC2, DOHC motor with automatic. SES light came on, and its a code P0420. I researched on here and people say that's a bad cat. But with this car, there's a good bit of smoke coming out of the exhaust, like its running rich? I think the upstream O2 sensor is bad and the a/f ratio is off? Might this just be 1 or both o2 sensors?

Also, in terms of replacing the cat. Will universal cats work? I see them on Amazon for about $60.
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Old 06-08-2021, 12:34 PM   #2
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Default Re: P0420 and smoke

No, the P0420 is probably not from the S1 or fuel trims. Could be a bad S2, though.

What color smoke, white grey, or black?

Use live-data to check out the O2 sensors and fuel trims, why guess?

As to the replacement cat, it will depend on what state you are in and the specific requirements that must be met.
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Old 06-08-2021, 04:36 PM   #3
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Default Re: P0420 and smoke

Quote:
Originally Posted by billr View Post
No, the P0420 is probably not from the S1 or fuel trims. Could be a bad S2, though.

What color smoke, white grey, or black?

Use live-data to check out the O2 sensors and fuel trims, why guess?

As to the replacement cat, it will depend on what state you are in and the specific requirements that must be met.

Does S2 set a/f ratio?

It'll be complicated for me to get access to a $800 scantool. Or are you saying the cheap free scan from autozone will show that? I thought they only gave you codes?

Guessing at the problem is easier, because O2 sensors going bad is a common thing. I had a similar problem with my S10 when I got it, 1 of the O2 sensors was bad and the a/f ratio was off. For some reason the OBDII computer couldn't seem to tell, it only said the catalyst was bad (cat was fubar from the bad O2 and running rich). Had to replace the cat and 1 or 2 O2 sensors I forget exactly. I'm hoping with this might be catching it before the cat is totally bad? The SES just started turning on.

The smoke looks grey, like normal exhaust smoke, just more of it. Doesn't smell sweet, the car's never been overheated, but I haven't had a chance to check other things like compression, oil cap, coolant reservoir etc (its not my car, its my father's car). Usually his car has blue smoke from burning oil (these Saturns seem to burn a lot of oil).

I'm in GA, I've had universal cats put on cars before. Last time was like $50 labor and a $30 part years ago. RockAuto lists cats for this car from about $150 all the way up to $600+. To me a cat is a cat.

My main point though is, I don't think the cat failed just on its own. It may not even be completely bad.....this code is just showing a deeper problem. I'm thinking O2 sensors and a/f being off. O2 sensors for it are like $20/ea.

Last edited by nj9000; 06-08-2021 at 04:42 PM.
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Old 06-08-2021, 05:05 PM   #4
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Default Re: P0420 and smoke

Also meant to add, the only other code it has is for stalling. Forget the number, but all it said was the engine was at risk for stalling? Weird code, I'd expect a misfiring code or something like that.

Edit: This: https://www.engine-codes.com/p1599.html. Near-stall detected. With the smoke and P0420 I was thinking a/f.
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Old 06-08-2021, 06:50 PM   #5
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Default Re: P0420 and smoke

No, the S2 does not control AFR at all. It is there only to verify the cat is working OK. When you get that P0420 either the S2 sensor/circuit is bad, or the cat is bad.

Live-data can be had for far less than $800! An ELM327 link would be under $50, and a scanner that gives basic engine live-data (O2 and fuel trims) is likely to be in the $200-300 range. No, a scan at your FLAPS is of no use, unless they are willing to let you borrow the scanner to drive around with for a while.

If GA has only federal emissions requirements, then just about any cat available is probably OK. The shop doing the install should know what is required.

As to the other code, or drivability issues, take compression, take fuel pressure readings, and use that live-data to check all the engine sensors and parameters. Or, throw parts at it . . .

Last edited by billr; 06-08-2021 at 06:55 PM.
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Old 06-12-2021, 01:22 PM   #6
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Default Re: P0420 and smoke

The smoke is probably burning oil and that oil has killed your cat. Time to decide how much you like the car.
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