P0420 Code... CAT or O2 sensors?

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Originally Posted By: mrcoolguy
My car throws P0420 and P0430 codes...but thats because my car doesn't have any cats
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There are tuners (actual people, NOT hand held devives) using EFI Live and such who can write those codes out of your ECM (if you are speaking of your f body).

But that will not do you any good in draconian Cali, since they also do gestapo-like visual inspections for actual, real, functional catcons and hooked-up rear O2s, as well as on-dyno sniffer tests.
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Quote:


There are tuners (actual people, NOT hand held devives) using EFI Live and such who can write those codes out of your ECM (if you are speaking of your f body).

But that will not do you any good in draconian Cali, since they also do gestapo-like visual inspections for actual, real, functional catcons and hooked-up rear O2s, as well as on-dyno sniffer tests.
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Yeah, I am going to get some goodies first ( LS6 intake, heads, cam, LT headers and ORY pipe before I get a tune). I will have to pay for it to be street legal LOL
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[censored] Cali ...
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Ok.. I want to try to diagnose this myself if possible. I should have some time this week to pull the code.

I am just wondering... I have a scangauge II, but it is not the updated version with the XGauge capability. Do/can any of you who have one of these scanners look at the O2 sensor data with it? I will spend the $25 to upgrade mine if that is possible. Or, I could try to sell that and get a more advanced scanner for around $200 that will read the O2 data. I called a local shop and they told me labor just to find out who/what the culprit is would be $100... I can easily change out the sensors myself - hoping this is the issue!
 
I've posted this info in other threads re. P0420 codes and will offer my 2 cents about what has worked for me. Your cat and secondary O2 sensor probably do not work as well as they did when new causing an occasional check engine light. Before I replaced either part I would dump a bottle of techron, or regane in the tank, warm up the car and put the trans in 2 and do some alternating high throttle and coasting between 30 and 50 mph up and down a country road or some such safe place. After 8-10 reps of this I would hit the highway for 10 miles or so then come back and repeat the process. The goal of this would be to get the exhaust system and cat plenty hot in order to burn off any deposits in the cat or on the O2 sensor. It also couldn't hurt to do the plugs and clean the throttle first if they haven't been done. Then reset the light if it doesn't go out on its own.
 
The answer was posted here multiple times.

The cheapest scanner to verify weak catalytic converter costs $14.50 assuming you already own an Android platform such as a Smartphone or Tablet. It will just confirm the diagnosis of your converter falling off the the so called 95% efficiency cliff with 99% accuracy. There is a 1% chance that your primacy O2 sensor could be bad.

LicenceToKill:-
Can you tell me how long it has been since you used your method to get rid of P0420?
 
ok.. so I found the last smog check.. done on 7/20/10 so it will most likely have to be tested again in July as CA does biannual inspections.

Here were the readings - keep in mind they put cars on the dyno.

15MPH Test: RPM@1794 HC PPM:37 (MAX:50) C0: 0.27 (MAX 0.64) NO PPM:444 (MAX:508) PASS
25MPH Test: RPM@1765 HC PPM:9 (MAX:34) C0:0.00 (MAX 0.78) NO PPM:22 (MAX:761) PASS

does it seem like the converter either wasn't fully warmed up... or does it seem to need replacement? Or can you even tell from these results?

I priced sensors today.. about $220 for both upstream and downstream Denso (OEM style sensors)
 
Its hard to tell from these reading if there is any problem.
IMHO keep this as simple as possible. O2 sensors do get slow, in fact for many years some companies recommended 30K change intervals.
Today they can go much longer but personally over 100K i change them if i suspect a problem.

Whenever you change a cat its a good idea to swap them out anyway especially if they are in the 100k range, so swapping the O2's first makes sense.
If that doesn't cure the problem then you can change the cat. +1 on the Denso O2's, they are quality units.
 
Thanks Trav..

I think I will run a bottle of techron, go burn some mileage on the highway, and get the O2 sensors on order, and go from there.

James: I just replaced the spark plugs with OEM Iridiums at 100k and also cleaned the TB at that time.
 
^As a note, the longer a PEA containing fuel system cleaner can remain in the gas tank the better. It isn't a stripping solvent but a detergent that is best used on a full tank that you will use over a longer during of time.
 
Update:

I took the car out for a nice drive this past weekend with lots of high RPM miles to heat things up. Then as luck would have it, got a flat tire (sidewall) and interrupted my work. Anyhow, I replaced both O2 sensors, and reset the ECU. I also cleaned the MAF and cleared the codes. We will see what happens. I *did* notice the exhaust had a different smell when letting the car idle. Before the sensor changes, the exhaust smelled in excess of fuel. Now, not so much, so hopefully things are better! If not, I suppose a cat replacement is in order!
 
Sidebar on the Flat: I jacked the car up and put the spare on.. and continued working on the planned o2 sensor changes on Sunday. Yesterday I took the car and tire to Americas Tire since I bought the tires (and replacement certs) from them. They ended up replacing the tire for free, so I just had to pay the CA environmental tax, and a new certificate. I also opted to purchase a second new tire to have a "matched" set of tread since the other tires are at about 4-5 32nds of tread left. I hope I'm done spending money on this car for awhile, but it is the wife's car... It is comfortable, safe and is relatively inexpensive to drive - less than a new car payment every month, and safe for her and the kids to run around in.
 
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