Code P0420-Catalyst Efficiency Below Threshhold Bank 1

The saga continues. NEw 02 sensors eliminated the CEL for a few hundred miles and a second set of catalytic converters for 1200 miles but now it is back, same code as ever. The cat cons are not Subaru OEM, but do have an 8 yr/50,000 mile warranty and were $600 less than Subaru ones.

Any other more offbeat ideas of what's going on here?

TIA Jim

There are diagnostic tests. A scope will indicate to a competent technician if the sensors are switching fast enough with the proper out put voltage. tailpipe gas sniffers should tell a tech what's up with the converters. A coupla other ideas - bad ground or other electrical connection. bad/intermittent ECU.

Carl

I propose that perhaps your car is just messing with you. When my car does this, I just smack it hard. It never helps though...

But seriously. I have the same code, and am hoping it is the O2 sensor. I have a 95, and the rear O2 sensor is on the rear cat. I tried to get it out for about 45 minutes this weekend with no luck. It's hard to get enough torque on it to bust it loose. It seems that one of two things always happens, I have the wrench lines up correctly so that it holds, but then the damn sensor won't rotate, or I have it off a little and it just slips, slowly rounding the hex part of the sensor. I tried a plumbers wrench, but couldn't get it in there. I also tried some PB'laster, which usually loosens rusted on crap pretty well. I also tried running the car to heat up the cat. None of this worked. Any ideas? I've considered a torch on the cat close to the bung for the sensor, but dont[ know how smart that is. I don't know how much heat it can take. Any better ideas?

I could just take it to a shop, but I feel silly takign my car to a shop to have them unscrew something, and screw another right in.

Bill

This is getting pretty frustrating. I'm sure it would be at least as much so if I were actually a DIY person.

I know they scoped the O2 sensors both prior to replacing the front one (just checked the service record and only the front one has been replaced) and after replacement when the CEL came on again (and they were responding properly), I assume they did a sniff test (this is a state recommended emission repair facility) and I have repeatedly since the initial cat replacement) mentioned my concern about electrical and computer issues.

I suppose now they could tell me it's the rear O2 sensor. But I have no plans to replace anything further until after the car fails the state emission test in a couple months (they just read the codes, no actual tailpipe test) because I want any further expenditures credited toward a waiver if one is required. I'm environmentally concerned, but not convinced there's a real emissions issue (see last sentence of Carl's post above)

The next step is going to be Subaru cats, but given that the shop says they have had no problem with the supplier/mfr of the ones they used first and still on my car, I have a sneaking feeling this will not put an end to this continuing saga. I hope I am wrong.

Check engine light has gone out for a week or so. Burned out, or problem solved itself, or more likely, car messing with me...

If it makes you feel any better, I haven't done anything to mine, and it's coming and going with that code. I know I have a small hole in that cat though, according to the mechanic. Which of course is irritating because I'd paid a mechanice (who's since fled to Mexico) for a new cat about a year ago.

Seems maybe that brand of gasoline makes some sort of difference, but I can't say exactly how.

The rubber will meet the road here soon though--emissions testing flyer came in the mail last week. LOL.

-- Todd H.

I think my emissions test invite is due any day now too. Last done in June of 2007.

Car continues to mess with me.

CEL light was on, then off for 750 miles or so, and is now back on. Proposal is to return the aftermarket cats and replace with Subaru ones. But I do wonder about one thing. When the CEL came on again after being off,, I took the car in to have the ECU scanned. While code P0420 remains in memory, according to the shop, the car was listed as currently passing all tests (my paraphrase of what he said). So although the shop insists the ECU itself cannot be an issue, I wonder if the CEL light on but "currently passing all tests" make sense. I know it can go off by itself after coming on from the P0420 code.

Jim

My 2 cents.

Subaru implemented a program last year to help the Subaru tech ACCURATELY diagnose the p0420 code. It seems as tho Subaru Warranty was replacing too many of them that were not defective. Unfortunately, the test requires a scan tool that can graph live data and are watching for specific reactions between the ft AF ratio sensor (or o2 sensor in older vehicles) and the rear sensor. It requires driving at specific speeds and letting off on the throttle to trigger a response.

Having worked in the aftermarket world, I do not support the use of aftermarket o2 sensors and cats. On my dad's own truck, the aftermarket o2 sensor didn't work correctly and required a ford OEM sensor to cure the issue. Aftermarket cats often do not fit correctly (Mom's car caught fire right after she traded it in - I had nothing to do with that!) or don't quite work correctly. The data is in a pdf format on the shops laptop/scantool, and I cannot seem to be able to transfere it to show you. I will try to transfere some of the important parts of it soon.

I fixed this issue on a late 90s Legacy by swapping out the entire Y-pipe/CAT/O2 sensor assembly with one from a wrecked car.

Technically, I don't think the salvage yards are supposed to resell emission control hardware, but if you ask nicely, and ask for a "Y-pipe" or "Front exhaust pipe" rather than a "CAT and O2 sensor", you'll probably be able to land one.

It's been awhile, but I seem to remember spending $150 for the assembly.

Hope this helps.

ByeBye! S.

Steve Jernigan KG0MB Laboratory Manager Microelectronics Research University of Colorado (719) 262-3101

Well, I gave in an had a Subaru branded cat put on in July and the CEL has never reappeared. I guess the problem really was in the prior replacements.

thanx for updating the group on this. It may help someone doing a search for info in the future!

There's always the anti-fouler trick...

Dave

snip

There's always the anti-fouler trick...

Dave

Hey Dave,

What is the anti-fouler trick?

Thanks,

Dave K