My 2011 Prius "check engine" light came on...

What's the miles, is it burning any oil, and how much?

 

The catalyst elements in the converter can get very slowly 'poisoned' over time by various substances in the exhaust going through.

The car monitors for this by running a test every so often for the converter's "oxygen storage capacity". It's a fairly sophisticated test that does need both the upstream and downstream oxygen sensors to be working, but isn't so likely to give a false result if they're not; more likely you'd then get one of the other codes specific to an oxygen sensor problem, and the OSC test just won't be run until that's fixed.

When the needed sensors are all working right, the test works like this: sometime when the driving conditions are right and the engine's warmed up, the ECM will reduce the fuel injection a little to make the mixture lean. That means there will be extra oxygen in the exhaust, some of which will be 'stored' in the converter. After doing that for a while, the ECM will switch to injecting extra fuel, making the mixture rich, and watch the downstream sensor to see how long it takes to read the reduced oxygen level. How long it takes reflects the converter's oxygen storage capacity, so longer is better. Over the years it slowly declines.

A scan tool that can do "mode 6 intermittent monitor queries" can show what the last tested OSC value was. A higher number is better. I think you get the code when it falls below 0.240 or so. I'm not sure what the units are.

There are products that claim you can pour them in your fuel tank and drive around and they'll unpoison your cat, and maybe they don't. There might be more hope in a study I saw that taking the thing off and pumping a heated oxalic/citric acid solution through it for some hours might do the trick, but I've never tried it, and it would be quite the operation on a Prius where the two catalytic converters are part of a whole welded exhaust pipe assembly that also includes a heat-recovery exchanger and a resonator. I guess you'd have to pump the acids through the whole shebang. I'd guess the heat exchanger's stainless inside so it might be ok.

I would be interested if anyone around here ever tried it, and posted the car's OSC test readings from before and after.

 

Hmmm... Would it be this one?



Would it mean, mine is _very_ close to failing?

Mat

 

Mine is also very close to the minimum ... and has been for years. It doesn't seem to decline very fast.

 

I made a diagram of the data I have from my past diagnostic tests:



The highest values seem to be taken after longer and faster trips (but not all of them).

Mat

 

In case we're comparing, at a little past 150k miles, I got 0.252235 vs. >0.249795 expected, so also very close. I wonder why that minimum doesn't match Lares_Mat's.

 

The catalyst test varies day to day and week to week. No rhyme or reason.

Each of these followed the last by three to seven days:

 

It is really very interesting.
My minimum is 0,2196 and yours and rjparker's are 0,249795 (what software gives you the six digits after comma?).
At the moment, I can only think of my Prius being a european version and yours are probably US-versions.

It would be interesting to read what is the minimum by ChapmanF. As I remember, he has done the latest (optional) update to the ECU - my ECU is updated as well.

Mat

 

My 2012 v has the latest ecu software and the updated egr valve. Original cats and sensors.

 

So, it is probably the EU vs US version - it would be nice to know

Mat

 

I'm not sure that my 'min' value is always the same. It puzzles me. Perhaps the car computes the min passing value itself depending on some circumstances at the time of the test? I do not see it explained in the manual at that level of detail.

Seeing a PID value to six decimal places is probably just a matter of using software that blindly carries out the indicated scaling arithmetic without bothering to round off at the expected precision of the data. My 9th-grade science teacher used to harp on us for using our pocket calculators that way.

 

I can assure you, all my tests had exactly the same min value of 0,2196.

All results I've seen here had until now the min value of 0,249795.
Could you check yours?
Could someone from Europe, reading here, possibly check his values?

You are probably rihgt.

Mat

 

I posted mine a few years ago. Looks like Techstream displayed my min as 0.249.

Maybe it's the 'min' of the EGR flow test that I remember seeing move around.

 

And the test value as 0,251 - it's 0,002 difference...

Yes, the EGR flow minimum is fluctuating a bit.


And here you see my diagram with the differences to minimum (the red one with the right y axis).
You can see how ridiculously small they are. Maybe this is the reason some software takes so many places after comma.

Mat

 

I watch them for years and min value is like yours.
Wrote few words here Best ways to test the catalytic converter? | PriusChat

 

I suspect the US standard is different than the rest of the world.