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Thoughts?
Thoughts?
My question is - when you get this code, how definite is it that the catalytic convertor is bad? How long can I wait to replace it? Fortunately, I went immediately to get an emission test done and the van passed. So I can get my tags with no problems next week. It is suspicious that the light went off on its own. I don't want to spend money on this if it is not necessary. But, I don't want to get stranded with kids in the van. The only thing I can think of that was different, is that I was overdue for an oil change. But, not enough overdue that the "maintence required" light came on.
I would welcome any words of wisdom. Thank You!
So, on to your code... The code you logged was from a reading by the rear oxygen sensor, located behind the catalytic converter. While the front O2 sensor plays a real feedback role in regulating mixture, the rear sensor is just a tattletale device ratting you out to the EPA as a person of low moral character (just kidding...). It is suggesting that there is a real problem, but in no way impacts driveability, emissions, etc. If it wasn't that many states will not grant inspection stickers if this is a hard code, you could drive on forever with perhaps minimal impact, other than a sooty exhaust.
Now in reality, continuing to drive this way could eventually result in a clogged cat, which could degrade performance. So you do want to know why, and get it fixed.
Why did the light go out? Your system has several 'tiers' of code notation, ranging from "something happened, but it might just be an aberration", all the way up to "DEFCON 5" Armegeddon.
"Something happened" codes can go away in as little as 3 'drive cycles' (basically cold starts with some driving). More severe but fixed items go away after 40 cycles.
Sounds like your rear sensor might have sniffed out a one time burst of rich mixture, and it went away. Time will tell if it will return. Summer/Winter crossovers are common times for this to happen, as gasoline is 'reformulated'. Long drives with one pedal position & constant speed followed by a sudden off ramp (a big change in system status) have been known to trigger it on marginal systems.
Proper diagnosis can be difficult but it is essential. It could be a degrading cat, a dirty or compromised O2 sensor, bad wires or connections, or a computer issue. If you don't know what is broken, fixing it can be very costly!
And that concludes tonight's lesson!
good luck
Based on past experience I first check the internet for fellow sufferers to see if there isn’t a simple fix and an avoidance of the dealer. Sure enough this is yet another common issue. A loose gas or defective gas cap seems to be a common problem. Checked, but not my problem.
Next seems to be a faulty oxygen sensor, e.g. dealer and money. After only 21k I didn’t think it was likely (or maybe it was hope it wasn’t likely).
Third most common is a recent tire change affecting the ABS and thus the Check Engine and VSC Trac lights which activate evidently to protect the systems. I did have to replace the front tires already, but that was some time and miles ago, so I doubted that was my issue.
Fourth, and way too common with Sienna’s, a faulty sensor reading. A solution to this possibility I found on fixya.com – disconnect the negative terminal on the battery for a few minutes. The lights are now off.
My Sienna is painted red; it should have been painted yellow for lemon.
You could also force a clear by disconnecting the negative for a minute or so and if it doesn't return all's good. Mine is still off after many on and off cycles and a couple hundred miles.
I highly advise you to buy a code reader with a clear/reset function, and use that instead of disconnecting the battery. Some of your problems may be directly related to this practice, and Toyota has advised against doing this in multiple publications. TT-0086-11 is one of the more recent ones that list recovery procedures from poor driveability after a battery disconnect. These vehicles rely on 'learning' and stored values to compensate for age and wear. When you wipe the memory, you reset to original factory specs, and the vehicle can really be at odds with these values. Doing this wipes out idle settings, short and long term fuel trim, ignition timing, etc. This can result in false oxygen sensor (front A/F and rear O2) codes, or even converter degradation.
VSC & Trac *may* come on, depending on what the logged code is. It usually accompanies issues that impact driveability, and not necessarily just simple emissions issues.
Some codes set on a single incident, some after failing several tests in a sequence. Codes can go away in as little as 3 passing drive cycles, some remain up to 40.
I've not seen a code set just because of a tire change, although I suppose that earlier indirect TPMS could - especially if you have severely mismatched tires that result in a substantial rotational difference? I'd be interested to know more on this one.
Sienna 2004...Just found out , the cel, vsc and trac off may come on if you change the air filter and disconnect the wire harness from the top of the filter housing. In this case it did throw air intake / mass airflow sensor codes.
My conclusion:
Any time you get a cel after disconnecting any wire harness while working on the engine,
it is a good idea to reset the cel first, and see if it is bogus, related to the disconnect before taking it to the dealer.
If there is a real problem, the cel will come back on.