Check Engine Light Issue

[Duckhook1]

My daughter has an '03 Vibe GT. It now has 155K on it and has generally been very reliable. We live where an emission check is mandatory every 2 years in order to renew your registration. So... a little more than a month ago, her check engine light came on. We took the car to an independent repair shop that we have used before and has a good reputation. They read the fault codes and found a bad oxygen sensor and catalytic converter. They replaced the oxygen sensor and then sent us to a muffler shop for a new catalytic converter. Perhaps 100-200 miles later, the check engine light came on again. I took the car to an AutoZone and they read the fault codes. There were 3: P0130, P0133, and P0420. I took the car back to the first independent and they looked the car over and recommended that I take it back to the muffler shop. I did so and they replaced the converter on warranty. About 100 miles later the check engine light came on again. I had the codes read and this time the only code that came up was P0420. So again I took it back to the muffler shop and I watched as they welded in a new converter. We gave the car back to our daughter last night and the check engine light came on again as she was driving home.

Now after an oxygen sensor replacement and 3 converter replacements we still have the check engine light on. Has anyone had a similar experience and if so how did you resolve it? I'm open to any and all suggestions.

Thanks

[Salsa Guy]

Which O2 Sensor they replace? There is 2, one in the Front (in the exhaust Manifold area) and 1 in the Rear (after the CAT). If you replaced the CAT and still have the P0420 then you may need to replace the rear O2. The P0130 and P0133 can be fixed by replacing the front O2. If you replaced both O2 sensors and the CAT buy a $10 Defouler then put it on the rear O2 and call it good. The P0420 is when both O2 signals mimic each other and the ECU sees it as a problem with the CAT.

[triz]

Also you might want to check what brand 02 sensor they used. These cars are picky and some like only factory 02 sensors.

[Salsa Guy]

I buy Denso products for my car because they make them for Toyota. Bosch also makes quality stuff also.

[Duckhook1]

Thanks for the replies. They replaced the front sensor. I will have to check on what brand they used. The P0130 and the P0133 codes have gone away. We are only getting the P0420.

I've not heard of a $10 defouler. Can you explain?

Thanks in advance.

[kumquat]

Sounds an awful lot like a bad downstream O2 sensor.

[Salsa Guy]

A defouler is like an extension for the O2 sensor. It basically deadens the activity of the back O2 so it doesn't mimic the front o2.

[JohnO]

+1 on the rear Oxygen sensor. The whole problem all along could have been 2 bad Oxygen sensors. What are the odds? You could have got a hold of some bad gas that did them both in.

[kumquat]

+1 on the rear Oxygen sensor. The whole problem all along could have been 2 bad Oxygen sensors. What are the odds? You could have got a hold of some bad gas that did them both in.

I was kinda thinking along those lines. Something could have fouled up both O2 sensors. And the cat, too, actually.

[Salsa Guy]

If you are blowing oil or antifreeze out the exhaust then it could foul the cat. But then you would have a much larger issue.

[Duckhook1]

Engine doesn't burn oil and is not blowing antifreeze out the exhaust system.
I found info on spark plug non-foulers. Will pick up a pair and install. I'll let you know what happens.

[kumquat]

Engine doesn't burn oil and is not blowing antifreeze out the exhaust system.
I found info on spark plug non-foulers. Will pick up a pair and install. I'll let you know what happens.

What? No. Don't do that. Why would you do that?

The most obvious culprit here is a bad/fouled post-cat oxygen sensor. Don't go installing unnecessary products on your spark plugs.

[triz]

If the the post 02 sensor was changed you might want to check for any exhaust leaks that can also trigger that code.

[Salsa Guy]

You only need one defouler on the 2nd O2, leave the 1st O2 alone. An exhaust leak around the manifold could be a issue.

Also dumping raw gas into the CAT could cause a problem which could be caused by a bad 1st O2.

How has the MPGs doing? Getting High 20's low 30's?

[Duckhook1]

I think that the problem is solved. I purchased defoulers and drilled one out to 1/2". When I took out the rear O2 sensor, I found that its diameter was too large to fit into the 1/2" hole in the defouler. I went ahead and bought a Denso direct fit sensor and installed that with the defouler. My wife has been driving the car for a couple of days and so far the CEL is staying off.

Interestingly, I yesterday I took my 911 Porsche to an independent shop to prep it for winter storage. I was discussing my Vibe problem with the owner and he told me of related issues with Porsches. He found that often after changing to an aftermarket exhaust system, the CEL comes on. They then do the same thing as was suggested to me for the Vibe, and that is, use a defouler to move the rear O2 sensor out of the exhaust stream. Seems to work for Porsches too.

Thanks to all for the help.

[Duckhook1]

Forgot to comment on other suggestions.

Yes, there was a bit of an exhaust leak that I noted earlier. Replaced the donut and the leak went away. This was after having the cat replaced for the first time. Didn't change the CEL.

Mileage has always been in the mid-20's to low 30's. So we haven't seen any change in mileage even while having the CEL problems.

[mntn-biker]

What is the o2 sensor diameter after the CAT? Is it 18mm? I have a 03 base if it matters.

[joatmon]

The one time I took out the O2 sensor behind the cat on my 03 base, I used a 7/8" wrench, so that puts it at more like 22mm. That is if you were asking about which tool to use. I don't know what the diameter of the actual sensor is, but I think that when I drilled out a spark plug antifouler to make a O2 sensor desensitizer, I used a 1/2" drill bit , that puts it more at around 12mm.

in viewtopic.php?p=402485, frankenvibe says that the threads on the O2 sensor are likely M18x1.5mm and in viewtopic.php?t=47790 nato says the threads are in fact 18mm