I have had a check engine light on with a P0420 catalyst code. I already changed the downstream O2 sensor. It will run for a day or so before the engine sneezes or something and the light comes back on. Seems the cat is right on the verge of not working or it would trigger it right away (I think) but doesn't seem to be plugged at all because the car runs great. There are no emission tests in FL and am now asking thoughts on the spark plug non fouler trick between the O2 sensor and the cat.. Thanks for advice.
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Probably the cat conv is toast, as the code says.

 

I fought this on a different car ('98 Explorer V-8) turned out to be the upstream sensors. I cheated smog tests for years by resetting the computer. Then it finally grossly failed an emissions test about the same time I realized my MPG had gone to hell and power was a bit off. The computer showed no O2 fault codes and live data showed they were working perfectly, but a Ford specialist adamantly said it was the upstream O2s. I put in a set of used ones I had laying around and perfect. Passed emissions with great numbers, economy is better than ever, no more P0420.

Those cheaters or the electronic ones may get the light off, but if you have another problem you're masking then you may end up actually damaging the cats that may still be good. Modern cats last seemingly forever if the engine is doing what it's supposed to.

 

Not so. I've had plenty of customers with 0420 and don't recall a single one that actually needed a cat except for one where the cat was rattling, core came loose or broke. Most just needed O2s and a few got neglected tune-ups done.

 

Thank you all for the input and advice.. I have been doing some reading up on this before and after changing the downstream O2 bank one.. I read somewhere that suggested trying Techron so I added a bottle and filled the tank w/18gal. Drove across FL and back on the express 70-80mph for 358mi. and the light is still off. Amazing. I just got back home and I'll see if the around town stop and go brings the light back. I'm pretty sure there is no restriction because it revs up very fast.

 

Any luck yet? Has the light stayed off? From what I understand, you want to change the upstream sensor, not the downstream one. Do you still have the old sensor, or did it get tossed?

Catalyst efficiency is determined by comparing the switching rates of the upstream and downstream sensors. The upstream sensor sees the "raw" exhaust. The PCM constantly keeps adjusting the air/fuel ratio at a very rapid rate, and the upstream O2 sensor values should reflect this rapid switching. Meanwhile, the downstream sensor sees the "clean" exhaust after the catalytic converter. If the converter is doing its job, there shouldn't be much switching downstream, just a fairly steady value. If the converter has failed, both sensors will rapidly switch up and down together, because no cleaning action has occurred passing through the converter.

As O2 sensors age, they typically don't respond as quickly. Since a slow switching rate downstream is actually good, you're better off with an old sensor there. By the same logic, a new sensor upstream is also good, to increase the difference in switching rates that tells the PCM the converter is working. By installing a new sensor downstream, you have inadvertently created a situation opposite of what you want.

If you still have the old sensor, I'd suggest reinstalling it downstream and then installing a new sensor upstream. I believe the sensors are the same except for the length of the wire pigtail. You may be able to swap the old upstream and new downstream sensors if the connectors will reach, but am not sure. I'm always leery to suggest just throwing parts at a problem, but upstream sensors are normal wear and tear items and should be replaced periodically anyway, so I won't feel bad if it doesn't fix the problem.

Also, keep in mind the P0420 code typically does not come on right away. I believe it has to be seen on at least two consecutive drive cycles to prevent nuisance messages. A scan tool will show the code stored as pending, but won't turn on the light until it sees the fault on the second consecutive cycle.

 

Just be careful because many cars use different O2 sensors upstream and downstream.
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Thanks for all that.. The short history after the downstream O2 change was a trip to Tampa and back and while there a few drives around town while there for 3 days.. The light did come back on second day home after almost 400mi.. Since the engine runs so well I presumed the upstream O2 were OK and have no codes to indicate otherwise. My limited understanding was that the upstream helped control the fuel mix along with the MAF, the MAP, intake air temp and the downstream were only to keep tabs on the Cat.. Have you ever heard of these O2 extenders for downstream only..
Oxygen sensor extender spacer | eBay

Quote extender claim."On ODB-II vehicles (96+), the ECU has two O2 sensors for diagnostic purposes. The first O2 sensor is located before the Catalytic Converter and is responsible for all the Air/Fuel tuning and is imperative to the operation of the vehicle. The second O2 sensor is there to make sure the catalytic converter is doing it's job properly. By Utilizing the O2 Sensor Extender to move the second O2 out of the exhaust stream on modified vehicles it will reduce / prevent the risk of throwing a CEL."

 

His upstreams don't work like that. They are linear aka wideband.

The downstreams do 2 main things:
1. fine tune fuel trim
2. check cat efficiency

Using extenders would ruin #1 so put your cats at risk (as well as reducing mpg).

 

O2 Simulator, mini catalytic Converter cel fix
YOULL NEED THE 90* ONES, DO BOTH SIDES REGARDLESS IF ON OR NOT, THEY GO ON THE DOWNSTREAM 02 WHICH ARE THE MONITORS

 

I strongly recommend replacing the upstreams. They're a maintenance item anyway, and may fix your 0420 as well. They can be bad and not trigger an O2 fault code if the computer thinks they're working right, in the meantime they can make your mixture rich overloading the cats triggering 0420.

 

Well, personally, I'd be hesitant to purchase anything from a company that doesn't hire a competent proofreader.

Should read: "its job", not "it's job".

Forgive me, I was a technical writer for 5 years. NOTHING got past our proofreaders...

 

It's is wrong here, but I've seen way worse grammar in parts descriptions and wouldn't consider that a reflection on the quality of the supplier. Its and it's are so commonly screwed up. I use the apostrophe for the possessive on accident too, being a drop out and having poor memory are my excuses.

Good thing they're not selling them in pairs, if they advertised O2 sensor's I'd cringe, but I see that misuse even on banners, ads, billboards...

 

Sometimes known as the grocer's (or greengrocer's) apostrophe here (though chip's for plural is probably the commonest).

It's just ignorance/poor teaching or sometimes hurried typing. Not helped by the inconsistent usage in English (a language with 5 rules and 5000 exceptions - or 5000 rules and 5 exceptions if you prefer).

 

"commonest"?!?!? You're just lookin for trouble aint ya. Your luckie the gramer police dont peruz the interwebz looking for victims.

Maybe we should rerail this back to O2's and cat's. I'm a noob so I don't wanna rock the Jag-boat to hard.

 

Walking along our high streets is a lesson in how not to use the apostrophe.

I thought the O2 details were covered already. What else?

 

Forget about the extender on the downstream sensor.

Here's what i would do.

Swap your sensors over left-right. Upstream and downstream.

If it stays as P0420 your cat is toast, and sticking an extension on the downstream sensor won't fix that.

If the P0420 becomes a P0430, then you have a bad sensor. In this case it would be the upstream one since you already changed out the downstream.

Simples...

 

I really didn't need a lesson on grammar but thanks.. Brutal is the only one who answered my question about the extenders fooling the sensor. After paying my taxes for all my life the US govt has allotted me $880 a month retirement because they spent it all and more on wars.. I'm trying to not pay $600-800 for cats to limit pollution when the Koch Bros. bribe the govt so they can dump millions on tons of pollution every yr.. I don't feel guilty..

 

Jag.. I appreciate your help..What else? OK... Please show me a thread where they discuss these extenders and if they work or not.. This post wasn't about the sensors but the cheap tube that fools them. At first I noticed the spark plug anti foul extenders that need to be drilled out and now I see them all ready to go so some must have been used with success on some cars. I was asking if any were used on a Jag.. Thanks again

 

Sure have a look here https://www.jaguarforums.com/forum/x...-remap-140980/ Here's a thread where we REMOVED the extenders / minicats from a car and got improved fuel economy and fixed incorrect fuelling, as noted by the air-fuel-ratio's measured with the car on the dyno.

Sure they've been used on Jags. They may prevent a check-engine-light if you have high-flow cats fitted, or even no cats. BUT they are not going to fix a bad O2 sensor or miraculously unplug a choked cat...

Your problem is a bad sensor or a failed cat.

If you have a bad upstream sensor then putting an extension on a downstream sensor won't fix anything.

If you have a bad downstream sensor then it might put the light out, but then it introduces other problems.

If you have a failed cat, then it might put the light out, but eventually you will have a heap of other problems from a failed cat.

Read the fine print here O2 Simulator Mini Cat Cel Fix best oxygen sensor simulator made.