How could 50 to 100 clearings of the OBD codes (using a dumb OBD reader)cause the catalytic I/M readiness monitor to set after months of notsetting?Can the complicated electronics modules be "saving" scores of prior memorysessions perhaps?The storey is a bit confusing because the pieces only fell in together wellafter the fact for each event, but here's the short summary of whathappened as I loosely recall the major happenstances of this purelyelectronic ordeal.[1] The check engine light has been on, on the dash, almost constantly[2] Mostly when I looked, it would be P0420 bad cat pending & set codes[3] I've been going through this regimen now, for about five or six years[4] I didn't need smog for more than a year so I didn't worry about codes[5] When it came within months of smog time, I cleared the OBD codes[6] Mostly either the code comes back or the readiness monitor won't set[7] But once in a while, the readiness monitor does set so I rush to smog[8] I did that - it passed smog - but failed for a hose in bad condition[9] I painted the hose black so that it would look like it's brand new[10] But then for another month I couldn't get the readiness monitor to set[11] At one point, I accidentally added gasoline with water (long story)[12] The car ran like hell for an entire gas tank until I refilled itAfter that, it passed smog and for months now, no codes.What happened?I have no clue.A miracle?A coincidence?I do not know.Maybe what "might" have happened is that during the time that I was drivingon the tank of watery gas, I had to keep the OBD code clearer on my lap.Within a mile, the engine would stumble and I'd clear the codes and theengine would run fine for another mile, and then it would stumble, and thenI'd clear the code and it would run fine for another mile, and so on.This I did for at least a hundred, maybe two hundred maybe three hundredtimes during the watery gas stage - but - miracles to happen I guessbecause after that, no codes and, get this, the...

It cannot. But the fact that you've got 50 to 100 clearings of the OBD codesmakes your general maintenance process very suspect.What this means is that the O2 sensor downstream of your converter is reading an incorrect value. This could mean your converter is bad, ormaybe that the O2 sensor is bad, or maybe that the connector is bad.If other codes were set too, it could have been all kinds of other things.If you're seeing incorrect values on both pre and post converter sensors, you'll see other codes, and that could be the result of all kindsof misfiring issues or mixture control issues.Have you considered actually finding and fixing the problem instead of constantly resetting the error? You're not doing your engine or yourgasoline bill any good this way.Wow, with maintenance like that it's a wonder your car runs at all.Maybe the converter was dirty and all the steam cleaned it out. Maybe youhad a fouled plug which was causing a misfire and the steam cleaned it up.Maybe you had a...

How could hundreds of clearings of the OBD codes cause the catalytic I/M readiness monitor to set?

Apr 23, 2023 Last reply: 3 years ago 28 Replies

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Peter W. 3 years ago

Why does this entire exchange remind me of Jimmy Neutron and its BMW? Fundamental lack of understanding, and a closed mind.

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Frank 3 years ago

I was also wondering how the fuel could be shut off to any cylinder since very few normal passenger car engines inject into the cylinder itself.

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Scott Dorsey 3 years ago

Your Sienna is injecting into the intake of each cylinder, so the computer has fairly independent control over cylinders. But there is still a very tiny amount of mixing in the manifold.

Cars that have direct injection (which include a lot of newer BMWs) inject directly into the cylinder rather than the intake. This requires much more rugged injectors and much more expensive ones.

--scott

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Xeno 3 years ago

More accurate fuel distribution between cylinders.

____ Xeno

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Hiram T Schwantz 3 years ago

On Sun, 23 Apr 2023 23:00:56 +0530, mike posted for all of us to digest...

Sni9pped for your pleasure!

Is that you Arlen?

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