P0420 but smog result good

Status
Not open for further replies.
PandaBear

PandaBear

Joined
Aug 5, 2002
Messages
23,166
Location
Silicon Valley
So this is one thing that I have no idea about. A car I'm bringing to smog has passed the sniffer test but either 1) failed because of CEL on: ELM327 with Torque said P0420, or 2) clearing the code and cannot / have not yet finish the OBD2 CAT and EVAP drive cycle. I talked to another smog guy and he said that since about 5 years ago they are starting to chase after the drive cycle and CEL, even if the sniffer test pass it would be a fail now.

The car in question has about 20 years, 150k miles, with original O2 sensor (I assume), as far as I can tell it uses 4 wire so it is a zirconium narrow band O2, instead of the wide band 5 wire O2 that cost $120 or so. A rock auto Denso upstream will cost around $50 shipped (needs 2 for a V6), or a Walker will cost about $30. A Cal Cat would probably be about $300 and the car isn't worthy of a new cat (it will go to Mexico or Africa instead).

Let's say the old O2 is lazy by now, and let's say both upstream and downstream are narrow band O2, does the upstream get worn out earlier than downstream? and therefore I can assume that the downstream is fresher than the upstream, and I can swap them and make them work better?

Or do both up and down stream get worn out the same way? and therefore I should invest in some new upstream O2s?
 
Originally Posted by PandaBear
does the upstream get worn out earlier than downstream?


YES, always.

I have NEVER heard of the upstream one lasting longer than a downstream one.

Originally Posted by PandaBear
and therefore I can assume that the downstream is fresher than the upstream, and I can swap them and make them work better?


It depends - - sometimes you can. Sometimes the plugs are different

You can't lose anything more than a little bit of time at this point.
 
Originally Posted by PandaBear
So this is one thing that I have no idea about. A car I'm bringing to smog has passed the sniffer test but either 1) failed because of CEL on: ELM327 with Torque said P0420, or 2) clearing the code and cannot / have not yet finish the OBD2 CAT and EVAP drive cycle. I talked to another smog guy and he said that since about 5 years ago they are starting to chase after the drive cycle and CEL, even if the sniffer test pass it would be a fail now.

The car in question has about 20 years, 150k miles, with original O2 sensor (I assume), as far as I can tell it uses 4 wire so it is a zirconium narrow band O2, instead of the wide band 5 wire O2 that cost $120 or so. A rock auto Denso upstream will cost around $50 shipped (needs 2 for a V6), or a Walker will cost about $30. A Cal Cat would probably be about $300 and the car isn't worthy of a new cat (it will go to Mexico or Africa instead).

Let's say the old O2 is lazy by now, and let's say both upstream and downstream are narrow band O2, does the upstream get worn out earlier than downstream? and therefore I can assume that the downstream is fresher than the upstream, and I can swap them and make them work better?

Or do both up and down stream get worn out the same way? and therefore I should invest in some new upstream O2s?


Swapping them would just move the problem to the other side of the cat, wouldn't it? You would likely still get a DTC, but it would just point at the new location of the previously bad sensor, I believe.
 
Originally Posted by PandaBear
So this is one thing that I have no idea about. A car I'm bringing to smog has passed the sniffer test but either 1) failed because of CEL on: ELM327 with Torque said P0420, or 2) clearing the code and cannot / have not yet finish the OBD2 CAT and EVAP drive cycle. I talked to another smog guy and he said that since about 5 years ago they are starting to chase after the drive cycle and CEL, even if the sniffer test pass it would be a fail now.


Maybe I don't know Cali smog tests but don't all OBD2 cars just get the codes scanned? Why does it get a sniff test?
 
Originally Posted by atikovi
Maybe I don't know Cali smog tests but don't all OBD2 cars just get the codes scanned? Why does it get a sniff test?

Because without a sniff test, my catless 911 passes visual inspection and an OBD2 scan.
 
Were the sniff test numbers really good, or were they up close to failing?
 
changing the front O2 helped in my case - had the issue at age of 17-18years and 250k miles on 4 cylinder nissan. It was burning oil a bit, and the O2 was "poisoned". Of course the (pre-)cat is also weaker by now, but not as much as the old front O2 makes it look. The P0420 shows up occasionally - 1-2 times a year now.
 
I'm guessing the P0420 is based on the pre-cat's efficiency declining, but the main cat is still doing a good job of keeping the exhaust clean, at least when the car is warmed up.

I've never really fixed a P0420 with replacing oxygen sensors, good luck.

There is some kind of cat-clean snake oil type product that you might try. Again, good luck.

The anti-foulers will work to make the code go away, but I would be surprised if CA isn't wise to this "trick". I haven't heard of anyone facing penalties for getting caught, but I wouldn't be surprised if they are pretty nasty.
 
Originally Posted by rooflessVW
Originally Posted by atikovi
Maybe I don't know Cali smog tests but don't all OBD2 cars just get the codes scanned? Why does it get a sniff test?

Because without a sniff test, my catless 911 passes visual inspection and an OBD2 scan.


Is this a Cali only thing? Around here, Maryland and Virginia, anything with OBD2 (1996 and up) just get plugged in and checked for codes and incomplete monitors. No sniff. Quick and easy. In VA, 20 years old and no emissions testing at all. Plus depending on the year, car can have up to two incomplete monitors. Have a car with a large evap leak that sets the CEL every 50-100 miles. Cleared the code, drove it around 10-15 miles until all but the evap monitor set, went straight to the station and got it passed.
 
Is this a secret car? Can we know the make/model/year?

You know each car has its own quirk with the same DTC.
 
Originally Posted by atikovi
Originally Posted by rooflessVW
Originally Posted by atikovi
Maybe I don't know Cali smog tests but don't all OBD2 cars just get the codes scanned? Why does it get a sniff test?

Because without a sniff test, my catless 911 passes visual inspection and an OBD2 scan.

Is this a Cali only thing? Around here, Maryland and Virginia, anything with OBD2 (1996 and up) just get plugged in and checked for codes and incomplete monitors. No sniff. Quick and easy. In VA, 20 years old and no emissions testing at all. Plus depending on the year, car can have up to two incomplete monitors. Have a car with a large evap leak that sets the CEL every 50-100 miles. Cleared the code, drove it around 10-15 miles until all but the evap monitor set, went straight to the station and got it passed.

I don't think it's a California-only thing, but they definitely do it.
 
The reason it may have passed the sniff test is as cars get older the requirements they have to meet are softened. So the P0420 is looking for OE results while the sniff test is only looking for a water down requirement.

Could be a weak O2 sensor, but that is more rare than a weak/bad catalytic convertor.
 
Originally Posted by fozzdesy2001
Try the spark plug non- fouler o2 sensor to fix this code. It should get you by until you can get it properly fixed. The guy that showed me this used it for 2 years then sold the car. I did it to pass inspection then bought a new cat and new sensors. Hate p0420 code! The most you have to lose is a few bucks and some time, good luck.


They do a visual under the car to avoid people doing funny business like this.

Originally Posted by mk378
Were the sniff test numbers really good, or were they up close to failing?


Somewhere between average and low, not close to failing at all.

Originally Posted by atikovi
Is this a Cali only thing? Around here, Maryland and Virginia, anything with OBD2 (1996 and up) just get plugged in and checked for codes and incomplete monitors. No sniff. Quick and easy. In VA, 20 years old and no emissions testing at all. Plus depending on the year, car can have up to two incomplete monitors. Have a car with a large evap leak that sets the CEL every 50-100 miles. Cleared the code, drove it around 10-15 miles until all but the evap monitor set, went straight to the station and got it passed.


Between 97 and 00 they do both sniffer and OBD2 scan, after 00 (or whatever year before 08) they do only OBD scan. Still has visual inspection to check for non-fouler and non CARB cat.
 
Originally Posted by JMJNet
Is this a secret car? Can we know the make/model/year?

You know each car has its own quirk with the same DTC.


97 Camry V6. FIL sold it to my expat coworker wanting a cheap car that last 2 years, so yeah I'm sort of on the hook to get this thing running. While diagnosing this car to smog I notice a few things:

It has a stuck open / lazy open thermostat, so the temperature on highway is always around 1/4 to 1/8 of the scale (slightly below 1/2 being at perfect warm up temp). The battery is 2 1/2 years old, and both alternator and battery checked out fine by AAA road side assist during a jump start, and the starter is recently installed Denso Reman. I've checked the front bank spark plug (only 1 of them), and it is Autolite Platinum +4 / +2 style electrode plug and relatively new. I have some Champion double platinum of the right model that I can swap in there and see if it works better. It had 1/2 a tank of 87 and 91 gas in there.

After the transaction we found out that my FIL is either ignorant or dishonest (I'd say about 80% ignorant and 20% dishonest). He took the battery out to trickle charge while parking the car, so the ECM has no drive record. The car has 2/8 drive cycle record incomplete: EVAP and CAT. It threw a P0420 when I was trying to get the OBD connection working when i was trying to smog and the smog guy wants to check the drive record before starting a retest (1st test fail because there's no drive record).

It also had some leak from the sun roof, the front 2 drain tubes will leak into the car and start shorting door locks and lights (likely also drained the battery on the 1st day my coworker got it), and even got the OBD / DLC connection to malfunction, and a puddle of water in the middle of front passenger floor. I sealed the sunroof up from the outside with a tube of DAP clearer than silicone sealant to solve the problem. This is likely the reason why the interior looks more aged than it should have been.

I told my coworker I can refund him and we both just walk away, but he also want it to work so he can have a relatively cheap car for 2 years, or longer. This is the last car for sure I'll help my FIL with, and he learn his lesson on not keeping a car in non operation status, and should sell it as soon as he is done with it. I don't think he'll learn how to preserve things in general, but he's too old to care about that anymore (73).
 
Last edited:
Spark plug non fouler: isn't a worn out former upstream functioning similar to a non-fouler installed O2? and isn't a less worn downstream functioning similar to a younger / less worn upstream? Technically swapping old parts are not considered cheating on smog, if I understand correctly.

Also why would there be california o2 sensor and non california for some brands (API, Ultra Power, Delphi, Bosch, etc) but not the others (Densoj, NTK)? They are all 4 wire narrow band, not wideband 5 wire.
 
Sell it to someone in a non-emissions state/county. If you know anyone in Michigan that wants it, for example, where they don't have inspection, and they'd be glad to have a rust-free Camry
smile.gif


Or even Arizona or Nevada, where they're less strict and will let you buy a cheap $100 non-CARB converter
 
I just replaced the cats on my Mustang to the tune of $600
frown.gif
. I'd occasionally get a P0420 and the exhaust smelled bad so it was time. No more code or smell.

CA WILL do a visual inspection so if you are going to do the defouler trick, you need to remove them and drive straight to the smog place before the CEL comes on. My FIL did this for years with his old Camry.
 
Last edited:
Originally Posted by atikovi
Originally Posted by rooflessVW
Originally Posted by atikovi
Maybe I don't know Cali smog tests but don't all OBD2 cars just get the codes scanned? Why does it get a sniff test?

Because without a sniff test, my catless 911 passes visual inspection and an OBD2 scan.


Is this a Cali only thing? Around here, Maryland and Virginia, anything with OBD2 (1996 and up) just get plugged in and checked for codes and incomplete monitors. No sniff. Quick and easy. In VA, 20 years old and no emissions testing at all. Plus depending on the year, car can have up to two incomplete monitors. Have a car with a large evap leak that sets the CEL every 50-100 miles. Cleared the code, drove it around 10-15 miles until all but the evap monitor set, went straight to the station and got it passed.
I got my car emissions tested late last year, my car was not ready even though I had not disconnected the battery recently so I had to go back. I was looking at the failed test paperwork and apparently in Ontario if you have a car that can't complete an OBD scan they will tailpipe test it. I'm not sure if that is a loophole for engine swapped cars or just old cars with malfunctioning electronics.
 
Status
Not open for further replies.

Similar threads

blaze2051
97 4x4 5.9L dodge ram O2 sensor B1S2
Replies
7
Views
430
clinebarger
V
  • Question
'97 Plymouth Voyager O2 Code PO140
Replies
11
Views
1K
Voyager97
M
Most important Cat. sensor?
Replies
14
Views
1K
MichaelRS
I
Need emissions help with '14 Pathfinder
Replies
13
Views
926
i6pwr
K
09 Flex with P0420 Code since 4 years.
Replies
13
Views
1K
SatinSilver
Back
Top