P0420 - Catalytic Converter Efficiency Below Threshold - Page 3 - Subaru Forester Owners Forum
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post #31 of 767 (permalink) Old 07-19-2007, 09:17 PM Thread Starter
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Quote:
Originally Posted by Peaty View Post
It's really best to put it through the throttle body so you can get it as evenly as possible in each cylinder. I found that at least on my XT there wasn't one located in a perfect position. If you slog through this thread:

Subaru upper engine cleaner

Vac lines are discussed, I think there are some photos and stuff there too.
I'd prefer to use a vac line, unless it is possible to pour (not spray) sea foam right into the throttle body?

Found 2 vacuum lines that look like good candidates. Can't say I know what their names are, but I attached pictures.
  • First line goes from the "Air Assist Injector Solenoid" to either the throttle body or just after the throttle body (by what looks like some sort of sensor.
  • Second candidate runs from the purge control valve to the main chamber of the manifold. For some reason, I didn't get a picture of where it connects to the PCV.
Is one of these a better option than the other? Thoughts? Suggestions?

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post #32 of 767 (permalink) Old 07-19-2007, 09:28 PM
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I just pour it in a very little bit at a time into the TB.


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post #33 of 767 (permalink) Old 07-23-2007, 08:41 PM Thread Starter
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Status update:
Was way too distracted by the beautiful weather this weekend to do any work on the car. Oh well.

Did the Sea-foam this afternoon. Used between a third and a half of the bottle. I was surprised at how long the smoke lasted. Luckily it's always windy up here in the copper country. Went on a spirited ride up the Keweenaw to clear the last bits of smoke out . The rest of the bottle will probably go in the gas tank.

Heading downstate this weekend, hopefully the CEL stays off, but I'll get an emissions check while I'm down there and see if there are any real problems.

Edit: Used the vacuum hose in pics 1-3, as it was the most centrally located, and easiest to access the other end of the line.
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post #34 of 767 (permalink) Old 08-29-2007, 09:21 AM
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I've had a couple very experienced techs tell me that doing mostly short trips is what is causes cats to die early...along with the engines.
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post #35 of 767 (permalink) Old 08-29-2007, 09:59 AM
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I'll try the $5 fix (mechanical fix) first.

Could you explain the $5 mechanical fix you referred to?
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post #36 of 767 (permalink) Old 08-29-2007, 05:23 PM
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Originally Posted by silenthorn View Post
Thanks Peaty, excellent instructions!

Went through the process described here. Didn't use SeaFoam (couldn't spray), but a similar carb cleaner product. Didn't notice any white smoke in the exhaust. Did I not use enough of the product, or does that just mean there was no problem? Maybe the white smoke was gone before there was a chance to cut the engine?

The can of sea foam says to feed 1/3 can through the vacuum line. Should I go ahead and try this? If so, which vacuum line?
I will be interested to hear your results. I'm skeptical that SeaFoam can clean a catalytic converter, since the hydrocarbon is combusted mostly before entering the converter. However, it's worth a try as someone said.

My Eastern catalytic converters seems to be working OK so far, w/ no return of P0420. I have not run my scanner to check for 2nd O2 sensor response pattern.

good luck

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post #37 of 767 (permalink) Old 04-09-2008, 03:53 AM
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UK '01 Manual All Weather Forester.

The annoying P0420 reappears between 70 and 200 miles. Two independent exhaust gas tests showed near-perfect lack of pollutants so I ended up looking at the oxygen sensors. There isn't much obvious information on these but I appear to have a wideband air:fuel sensor in the front, it has 5 wires and some device on the plug, another oxygen sensor? Is this correct?

The rear one seems conventional with 4 wires, (it's removal just brings up the "sensor heater missing" code).

I'd like to reflash the ECU to prevent P0420 appearing but, apart from anything else, I haven't found the ECU yet. On the RHS (driver's) there are the 2 green connectors but no sign of the unit with it's 3 connectors and mass of wiring. On the LHS there's mostly mouldings associated with the heating/air con. My wiring harness diagram is the US version.
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post #38 of 767 (permalink) Old 04-09-2008, 08:23 AM
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The front O2 sensor, also called the A/F (air/fuel) sensor is used by the ECU during closed loop operation. This sensor is critical for engine operation. As far as I know, it's not a wideband sensor, that would be expensive & not needed. The rear O2 sensor is used to monitor the efficiency of the CAT. The rear sensor on the '05+ is also used for fuel trim. If you're getting a CEL code P0420 & you're sure there is nothing wrong with your emissions (normal engine operation, exhaust pipe tip is not sooty), it could be as simple as a faulty sensor. Unlike the front sensor, these are not critical, so you could get a cheap one on the internet.

I don't think an ECU reset will clear the CEL code P0420, so you'll have to use a scan tool to reset it.

Bobby...

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Last edited by 2.5x_sleeper; 03-16-2015 at 06:44 PM.
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post #39 of 767 (permalink) Old 04-09-2008, 08:37 AM
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Quote:
Originally Posted by David C View Post
I'd like to reflash the ECU to prevent P0420 appearing but, apart from anything else, I haven't found the ECU yet. On the RHS (driver's) there are the 2 green connectors but no sign of the unit with it's 3 connectors and mass of wiring. On the LHS there's mostly mouldings associated with the heating/air con. My wiring harness diagram is the US version.
You mean reset the ECU? It won't clear the code... you'll need an OBDII reader like the ScanGauge II to read and clear codes. For future reference, if the SF is anything like the SG, the ECU should be under the passenger side footwell.

~ Silke ~
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post #40 of 767 (permalink) Old 04-09-2008, 05:52 PM
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I WAS getting the PO420 code practically all winter. It'd come, then go away, then come back, then go away... From what I've read on previous threads, running with this code won't hurt the engine since the code is from the cat, so I just let it go.

Funny thing is...it started once the snow started falling (I swear it happened the first time we had an accumulation). And since the last snowfall, I haven't seen the code at all, especially since it's been warming up.

It's made me wonder for a while now if environmental conditions may assist in kicking the code in.


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post #41 of 767 (permalink) Old 04-10-2008, 01:48 AM
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By reflash, Gentlemen, I did mean an ECU reprogram rather than a reset and I know it's possible to remove P0420 that way. I reset the CEL's P0420 regularly now with an ELM323 adaptor and Digimoto Lite with a long serial lead to the nearest desktop PC.

The front O2 sensor still remains a mystery with it's 5 wires. I managed to break into the rear one's wiring in a permanent, waterproof manner, so as to run an oscilloscope but I don't really want to do that on the front one so it must go into the ECU somewhere.
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post #42 of 767 (permalink) Old 06-15-2008, 07:37 AM
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Originally Posted by David C View Post
By reflash, Gentlemen, I did mean an ECU reprogram rather than a reset and I know it's possible to remove P0420 that way. I reset the CEL's P0420 regularly now with an ELM323 adaptor and Digimoto Lite with a long serial lead to the nearest desktop PC.

The front O2 sensor still remains a mystery with it's 5 wires. I managed to break into the rear one's wiring in a permanent, waterproof manner, so as to run an oscilloscope but I don't really want to do that on the front one so it must go into the ECU somewhere.
I have a Acura 2.5TL w/ a defective torque converter lock-up (P0740). Trans is fine otherwise, and I will live w/ no torque converter lockup rather than have trans overhauled. I would like to turn off the CEL, but this would require re-programming the ECU to "overlook" the torque converter slippage that sets the code. Your post suggests you have changed your flash memory to turn of P0420. Is it possible to selectively turn off codes? What tools or service would I need to do this?

thanks

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post #43 of 767 (permalink) Old 09-26-2008, 10:19 AM
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P0420

Well, it's time for Slynki's (98 S) bi-annual smog inspection, and she's failed twice now with a recurring P0420. First time we suspected she wasn't properly warmed up. Second time she got a good romp on the freeway before the test and still failed the sniffer due to running too rich at idle. What's the consensus on replacement parts in this case? She's got about 200k miles, so we suspect that her cat might be at the end of its intended lifespan. Should we just shotgun the problem and address the O2 sensors as well?

~ Silke ~
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post #44 of 767 (permalink) Old 09-26-2008, 10:35 AM
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Quote:
Originally Posted by silenthorn View Post
P0420 - Catalytic Converter Efficiency Below Threshold. The forester has been throwing this code for a few months now, typically shows up on long highway runs
I have the exact same problem. What did yours turn out to be?

-T
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post #45 of 767 (permalink) Old 09-27-2008, 06:12 AM
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It's been 1.5 yrs since I replaced my catalytic converter w/ an Eastern converter. This fixed the P0420 and it has not returned. The fit was not great (find my post on the subject for details), but it has worked well.

I monitored my rear O2 sensor performance for several months w/ my Obdscan interface and portable PC monitor to confirm the performance was consistent w/ failed converter.

good luck

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