I know, I know; Another Damn P0420 Post

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Aflegeal
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Joined: Sun Nov 15, 2020 5:06 pm

I know, I know; Another Damn P0420 Post

Post by Aflegeal »

Hey everybody, I've got a question for the vibe community.

Background: I bought a 2005 AWD vibe 2.5 years ago with 75,000 miles on it. The guy I bought it from had replaced the catalytic converter with a new Walker ( not great, I know) one at 70,000 miles. A few months after I bought it, the P0420 light came on. I replaced the downstream oxygen sensor with a Bosch and the light went away. I had a few months of bliss then it returned. Other potential symptoms include high idle in park (~1200 RPM) and transmission is hesitating to shift from 2nd to 3rd and 4th when engine is cold. So now I'm wondering next steps.

Possible Causes I've found in research:
1. Upstream Oxygen Sensor replacement
2. Test for vacuum leak
3. Replace Intake Manifold Gasket with new orange one
4. Replace PCV valve
5. Replace IAC valve

Questions I have:
1. What do you think the first step I should take? PCV valve seems easy to replace if it is clogged up, but I don't know how likely that is to solve it.
2. I have a scan tool and can watch live data so if the oxygen sensors are mirroring each other, then the upstream sensor should be replaced, correct?
3. Any other suggestions for what could be causing this dreaded P0420 on a newer catalytic converter?
Thanks everybody!!
zbyers
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Location: Sheffield, Pennsylvania

Re: I know, I know; Another Damn P0420 Post

Post by zbyers »

99% of the time P0420 is caused by a bad catalytic converter. The code itself says the o2 sensors are working, by determining the cat is below efficiency thresholds. The downstream o2 sensors only job is to tell you if the converter is cleaning the exhaust as it should.

If P0420 is paired with other o2 codes related to the front sensor, it's possible that sensor is bad. Outside of that, if you're burning oil, misfiring, etc. those could cause a cat to go bad. This has some good info about P0420.

https://www.carparts.com/blog/p0420-cod ... _LS5wUguTU

Do you have an infrared temp gun? You could use that on the converter to see if it is drastically hotter than the rest of the exhaust. If it's plugged, it would be.
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Aflegeal
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Re: I know, I know; Another Damn P0420 Post

Post by Aflegeal »

Thanks for the tip on the temperature of the cat. I'll look into that.

Follow up question on the catalytic converter; I read that the AWD has two cats, one just below the upstream O2 sensor and then the second one under the car. Does the first, upper cat ever go bad and could that be a possible cause of a P0420 code?

The guy I bought it from gave me the receipt from when he had the cat replaced and it says, "AP Resonator/ Converter Assembly, AP Rear Muffler Assembly, AP Exhaust Clamp, AP Exhaust Gasket, Bosal Exhaust Gasket" for the parts and "Replace Exhaust-Complete System" for labor. Does this sound like they replaced both the upper and lower cats? If they didn't replace the upper cat, might that be a logical step to take (if the lower cat is fine and not overheating (indicating clogged condition))?

Thanks for the help! I've learned so much from this community.
zbyers
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Re: I know, I know; Another Damn P0420 Post

Post by zbyers »

Upper cat is in the manifold. It is not likely they replaced that...and it is probably the source of you P0420. Pretty sure that is the cause on mom's AWD as we replaced the rest of the exhaust system.
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Aflegeal
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Re: I know, I know; Another Damn P0420 Post

Post by Aflegeal »

Update: I watched the O2 sensors while driving and they seem to be behaving properly. Upstream sensor is jumping around a lot while downstream is staying around 0.5, oscillating slowly up and down a little, and reacting to throttle changes. I cleaned the MAF sensor and PCV valve. Also decided to change transmission fluid and filter to help with sluggish shifting in the mornings.

I bought an infrared temperature gun and checked the temperature of the 2nd catalytic converter at the inlet and outlet. I can't really get to the 1st catalytic converter to check it's temperature so I'm
not sure how to check on that one.

According to the video by Eric the Car Guy, a cat should be about 100-150 degrees hotter at the outlet than the inlet and if not, then the cat is bad.
Mine was COOLER at the outlet, implying it is plugged up! This cat has a little over 20,000 miles on it and is already bad? I have read that you need to fix whatever caused the cat to go bad if you want it to be solved for real. So I'm wondering what all should be done to try and find / fix any issues that could cause a cat to go bad that quick.

I have plans to replace the intake manifold gasket, throttle body gasket, IAC valve gasket and clean throttle body and IAC. Should I change out spark plugs while I'm at it? Anything else I should address myself before taking it in in December for inspection and a new catalytic converter I guess?
zbyers
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Re: I know, I know; Another Damn P0420 Post

Post by zbyers »

What state do you live in? You could just gut that downstream cat, and then use an o2 sensor spacer on the o2 to trick the system. OR, since you technically have a cat as it is, you could just cut that lower one out and weld in a new one. I find it extremely unlikely that the cat you just replaced is already bad; it is more likely it is still the manifold cat.
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Aflegeal
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Re: I know, I know; Another Damn P0420 Post

Post by Aflegeal »

I am in PA. Is welding in a new cat a job that a regular mechanic does or are there specialized shops that deal with all things exhaust / muffler related?
Caretaker

Re: I know, I know; Another Damn P0420 Post

Post by Caretaker »

Aflegeal wrote: Mon Nov 23, 2020 9:09 am Is welding in a new cat a job that a regular mechanic does
absolutely. repairpal.com has it as an $1100 repair job, but I'm assuming that is including the brand new converter; Yowza!
jolt
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Re: I know, I know; Another Damn P0420 Post

Post by jolt »

Does the car have under 100,000 miles on it? If it does then the real question should be what is causing two cats to go bad in such a short time. The bad cat is a result of a problem and is not the cause of the problem. Until you fix the problem, you will continue to have cats go bad.

Shift problems; when was the last time the trans fluid was changed with the filter?

High idle speed when engine is hot; clean throttle body and idle circuit in body.

Cats will go bad from to much fuel entering cat. Use your scanner and watch the fuel trim numbers. How easy does the car start up when the engine is cold?
zbyers
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Re: I know, I know; Another Damn P0420 Post

Post by zbyers »

Aflegeal wrote: Mon Nov 23, 2020 9:09 am I am in PA. Is welding in a new cat a job that a regular mechanic does or are there specialized shops that deal with all things exhaust / muffler related?
If you have a local exhaust ship, swing by their place and they can weld in a new converter for you. I am also in PA, and don't have emissions here, so that's why many gut their cats or go catless. Obviously that's not the case for most of the state though.
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joatmon
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Re: I know, I know; Another Damn P0420 Post

Post by joatmon »

There was a member here early on, username pmh013. She had an 03 AWD, and it ate catalytic converters. Hers would clog, resulting in performance issues, dramatic loss of power, odd shifting behavior like downshifting while driving easy on a flat highway, horrible mpgs (or l/kn, if you prefer) etc. I don't think they ever figured out what was causing it, and she didn't keep it long, especially compared to some here.
Aflegeal wrote: Sun Nov 22, 2020 4:57 pm Update: I watched the O2 sensors while driving and they seem to be behaving properly. Upstream sensor is jumping around a lot while downstream is staying around 0.5, oscillating slowly up and down a little, and reacting to throttle changes.
That sounds like it is supposed to. Usually the test for a 420 is if the front and rear O2 sensor readings are too similar, then the car assumes the cat isn't converting. I tend to blame all 420s on a bad cat, but yours seems to have failed way too early with uncharacteristic symptoms, making me wonder if it is really the culprit. If it is, then something else is likely a core cause, which, left uncorrected, could get expensive
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Aflegeal
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Re: I know, I know; Another Damn P0420 Post

Post by Aflegeal »

zbyers wrote: Wed Nov 18, 2020 6:41 am Upper cat is in the manifold. It is not likely they replaced that...and it is probably the source of you P0420. Pretty sure that is the cause on mom's AWD as we replaced the rest of the exhaust system.
My mechanic says both converters are dead on my 2005 AWD.

( https://www.ebay.com/itm/Manifold-conve ... SwZ4dZMwNt)

(https://www.ebay.com/itm/Fits-Toyota-Ma ... SwVtZaPS1r )

I showed him these ebay links and he says he is uncertain if the manifold one will work since the description only says it fits an AWD Matrix.

Has anyone actually purchased this and put it on their Vibe?
Or is anyone 100% confident that it will fit an AWD Vibe if it describes it as fitting an AWD Matrix?

And last question; does anyone have a link for the gaskets that would be needed for replacing both converters? Between the manifold and first converter and between the first converter and pipe to the second converter?

Thanks for your help!
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