Quote:
Originally Posted by me and my metro
P0420 is almost always a dead cat. The description of your test conditions when the code sets are part of the drive cycle. That is when the cat efficiency test runs. What happens is the lean rich swings match on both sensors and this tells the pcm that the cat is not working. If the cat was working the two sensors would not have the same readings at the same time. I would try cleaning the cat that is between the two sensors.
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Thanks for the reference to the testing cycle. It never occurred to me that the testing might be intermittent and not constant. I have been thinking it is constant and that it sets a CEL when a dip below say 80 or 85% efficiency is detected. But
this website says the threshold is 50%. So according to the website, my car sometimes detects below 50% efficiency across two drive cycles and other times does not for weeks. What could cause intermittent efficiency drops like that? Maybe the gasoline of spark plug #4 is a hint?
Quote:
Originally Posted by oil pan 4
What I might try is get it tested, if it passes by a lot it probably is the O2 sensor.
If not the code is correct and catalyst is below efficiency threshold, try to clean it.
Converters have been using a lot of palladium over the years, palladium is near a 15 year high, so you don't want to buy one if you can help it.
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I would rather identify the problem in advance, not least because it appears there are other problems besides the CAT. What do you guys make of the gasoline on spark plug #4? Seems the spark is not firing completely sometimes, which might mean the gasoline/air mix is being sent straight into the CAT. If that happens when the ECU is running a test of the CAT and boosting the amount of fuel in the mix, then a gasoline/air mix burning in the CAT could possibly send O2 across the downstream sensor sometimes, no? That might trick the ECU into thinking the CAT has failed when actually spark is weak. No? Look at my picture of the CAT surface in my car. That's pretty clean: no melting, no cracking, no black spots, no flaky powder. Just some off-coloration.
Quote:
Originally Posted by Baltothewolf
Buy a spark plug anti fouler and drill it out to 1/2 inch and install it on the downstream sensor and just be done with it. Worry about it next time you have to smog it.
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As I mentioned in the OP, I have a SMOG test soon. Gotta get it done in July.