Failed Smog, High Emissions P0420 ??'s
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Joined: Jul 2010
Posts: 5
Failed Smog, High Emissions P0420 ??'s
I have a 97 V6 3.8l. I took it in today to try to pass smog for CA and failed horribly. In 2009 I had to pass smog because I had it non op'd for a while when the Fuel pump went out but that's another story. I wanted to get it smogged but had a P0420 code that popped up. I had the Cat replaced and it passed smog no problem. I drove it for about 6 months and then the light popped back on with another P0420 and because I have to get a smog check biannually it was time to take it in again. Well, I changed the rear Oxygen sensors, the ones near the cat, in front and behind, reset the code and was problem free. I took it in today to get it tested again and while it was being tested the error code popped back up again. It also failed horribly on the emissions.
15mph 25mph
HC Max 52 36
Meas 71 68
NO Max 424 711
Meas 776 759
As you can see it's almost double on the NO @ 15mph. I was wondering if anyone had any tips or advice on what to do next? Should I replace the front OS sensors? or is something making my cat go bad? Any help would be greatly appreciated.
15mph 25mph
HC Max 52 36
Meas 71 68
NO Max 424 711
Meas 776 759
As you can see it's almost double on the NO @ 15mph. I was wondering if anyone had any tips or advice on what to do next? Should I replace the front OS sensors? or is something making my cat go bad? Any help would be greatly appreciated.
1st Gear Member
Joined: Jul 2010
Posts: 142
From: San Diego/Frankfort, KY
sounds like a bad cat. Get under the car, tap the cats with a hammer. just tap them lightly. if you can hear ANY rattle inside, the cat is bad. How many miles does your car have on it right now?
Senior Moderator
January 2010 ROTM Winner
January 2010 ROTM Winner
Joined: Oct 2007
Posts: 18,306
From: The 'Burbs of Chicago
Make sure you don't have any exhaust leaks before the cat, that can throw off the post-cat readings.
And I find it hard to believe that your car could have trashed a brand new cat within 6 months, let alone break it apart inside.
And I find it hard to believe that your car could have trashed a brand new cat within 6 months, let alone break it apart inside.
Tech Droid
Joined: Aug 2005
Posts: 9,215
From: North East PA
Causes of high NOx:
Anything that will generate excessive combustion temps and/or bad or wrong type of cat. (need 3 way cat to pass NOx).
Such as:
EGR not working
Excessive spark advance (especially if pinging. bad KS)
Using lower octane fuel than actually requred
Excessive compression due to carbon build up in combustion chamber
Lean fuel mixture, due to bad O2 sensor, clogged injector making cylinder run lean, bad MAF, bad ECT
Bad cat
Anything that will generate excessive combustion temps and/or bad or wrong type of cat. (need 3 way cat to pass NOx).
Such as:
EGR not working
Excessive spark advance (especially if pinging. bad KS)
Using lower octane fuel than actually requred
Excessive compression due to carbon build up in combustion chamber
Lean fuel mixture, due to bad O2 sensor, clogged injector making cylinder run lean, bad MAF, bad ECT
Bad cat
Last edited by z28pete; Jul 5, 2010 at 11:17 PM.
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