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2006 Subaru Impreza Catalytic Converter

We have a 2006 impreza, that we’ve been told the Catalytic converter is going out. We cannot seem to determine if there are one or two converters on this car, and want to know if this is something that we could do ourselves once we find out where everything is at?

How many miles? You have an 8yr/80k mile warranty (more in some states). Who’s telling you this? How do they know? Have you had the oxygen sensor(s) replaced?

Agree with texases. The only indicator of catalytic converter efficiency is the oxygen sensors, and the sensors usually go bad before the catalytic converter does.

we are at 134K the dealer checked it out and said it was going out, but did not tell us if it was only one on the car or two. We have not had the sensor replaced. We would like to do this ourselves to save on the cost, but wonder if it is worth it.

it has been flashing the cruise control while the engine light comes on, it happens every 2nd or 3rd time i get gas and then go 60-70 miles. Had it checked by the dealer twice, and lights/sensor reset.

Have the oxygen sensors been replace? LOTS cheaper than cats.

no we have not had it replaced, to my knowledge

I would replace them first. What were the codes?

P0420 - had this checked in March 2013 and just a few weeks ago, same code both times.

Bad oxygen sensors will give a P0420 code. You can replace the sensors yourself. Don’t cheap out though, get good quality replacements. I think Bosch sensors are good. Denso may be the original sensor mfr, and those are good too.

Did someone just read a fault code or did they actually do the diagnostic procedure called for in the service manual when testing for a P0420? There’s a difference.

If a competent mechanic with the proper tooling diagnosed the catalyst as being bad then it needs to be replaced. If someone just spent 3 minutes reading a code you may or may not need to replace it, as a deteriorated oxygen sensor may be the cause. But this is easily discerned by a trained eye.

Also, it may under certain circumstances be necessary to replace the oxygen sensors anyway. I believe on your car they will need to be removed from the old catalyst and installed in the new. Sometimes they are seized in the pipe and need to be heated with a torch to be removed, or the threads may strip out on removal.

If the sensors are original I’d replace them either way.

How old are the sensors?

Just so that you are clear, all the P0420 actually indicates is that the readings between the upstream (before the cat) and downstream (after the cat) are too similar to one another. The downstream sensor is there to monitor the cat - the cat cleans up extra pollutants out of the exhaust so if everything is working well then the downstream O2 sensor will read much differently - it will be much less active.

However, the car’s computer knows nothing more than that the readings of the two sensors are too similar. It doesn’t know why. ONE reason why is a bad cat. And then there are lots of other reasons. This is a pretty good write-up:

The code is what is on my ticket from the dealership where i get all my stuff done on my car. I believe they are pretty competent people there, have suggested getting some things done elsewhere if it is too expensive, etc.I’m going to call my guy at the dealership service counter tomorrow. I’ll ask him these questions you all have brought up. Thanks for all the info and comments!

the sensors have never been replaced, original on the car. checked all my receipts tonight.

Your posts have implied though not specified - but correct me if I’m wrong on any assumptions - that the check engine light and code has been intermittent. It will come on apparently every few times you get gas? Then you have it checked and cleared and it stays off for a while. Then a while later, soon after you have gotten gas maybe 2-3 tanks later, it will come back on. Is that correct?


Then here’s a “theory” - take it with a grain of salt and for what you will. You’ll note on the URL I posted that things like a bad coolant temp sensor, engine misfires, or leaky fuel injectors can trigger a P0420. Those are all things that can send unburned fuel out the exhaust and through the cat. It’s possible to overwhelm it - send more through than it can handle. If this is a consistent problem that happens all of the time eventually at least a couple of other things will happen - 1) other codes might get set; 2) the cat will continually overheat, melt down, and then be finished for good.

But if it happens once in a while it might just pop that code once in a while and go away. One thing thing that can only occasionally and temporarily do this is a problem with the evaporative emissions system. These are the bits that capture and store your gas tank fumes and then send them to the engine to burn. Problems with the evap system can cause it to get liquid fuel into it - specifically when one fuels up. Then when the system “purges” its fumes, it ends up purging liquid rather than fumes and floods the engine. If you search these boards you’ll find multiple posts from people whose cars have trouble starting right after getting gas. The cause is often that sort of thing.

If you had such a problem, it could explain the intermittent nature of the error code and the coincidence that it follows fill-ups. Note that this kind of evap system issue could and perhaps should set other codes (e.g. evap system codes, rich condition codes) - but the computers are just not that “smart” and the interactions between things can be complex. There is a lot of tolerance for error in the programming.

I’m just bringing up up because it’s odd that it’s intermittent and that you connect it fueling up, and because - as asemaster noted and the URL I posted explains - nothing is as simple as reading the codes.

Thanks cigroller - I’m passing this info on to the garage and see what they have to say.