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Car Forum / Subaru Cars / May 2009Catalytic Converters
My ’01 Forester with 78k miles is getting an intermittent CEL. Had it in the shop for routine oil change and the code is pointing to the catalytic converter. The dealer shop quoted $700 for the parts, $150 for labor. Checking on line I’m finding catalytic converters for under $300 (for both front and rear). Some of the brands I am finding are Bosal, Magnaflow, Catco, DEC, and Eastern. Anyone have any experience, good or bad, with non OEM replacements? > My 01 Forester with 78k miles is getting an intermittent CEL. Had it > in the shop for routine oil change and the code is pointing to the > catalytic converter. P0420? > The dealer shop quoted $700 for the parts, $150 > for labor. [quoted text clipped - 3 lines] > Magnaflow, Catco, DEC, and Eastern. Anyone have any experience, good > or bad, with non OEM replacements? Search this forum for p0420. Some suggestions in that that would have one think twice about aftermarket cat and o2 sensors. I'm trying to solve this very issue on my vehicle as well. -- Todd H. 2001 Legacy Outback Wagon, 2.5L H-4 Chicago, Illinois USA >My 01 Forester with 78k miles is getting an intermittent CEL. Had it >in the shop for routine oil change and the code is pointing to the [quoted text clipped - 5 lines] >Magnaflow, Catco, DEC, and Eastern. Anyone have any experience, good >or bad, with non OEM replacements? I've had two pair on non-OEM replacement CATS put on (for about $1100) with better warranty (2 yr) than OEM (1 yr). Unfortunately the CEL/code P0420 keeps coming back. All other angles have been checked including replacing an 02 sensors. So as soon as the return details are worked out on the non-OEM, I'll be getting Subaru replacements front and back (for an additional $500+) Get your gaskets checked first. I blew through several O2 sensors and had all sorts of indication my cat was going bad before getting the final (bad) news that my head gasket was leaking coolant into the exhaust. Which will also screw up the sensors and throw errors. ESPECIALLY on the 01 motors. So, look in the coolant tank while it's running for bubbles, check coolant level, and get the coolant checked for hydro carbons before throwing another 1k at a problem that might not be that. >>My '01 Forester with 78k miles is getting an intermittent CEL. Had it >>in the shop for routine oil change and the code is pointing to the [quoted text clipped - 12 lines] > are worked out on the non-OEM, I'll be getting Subaru replacements > front and back (for an additional $500+) > Get your gaskets checked first. > [quoted text clipped - 30 lines] > > - Show quoted text - The head gaskets were checked at the last major service, and I don't see any other indications that they are bad. The gas mileage hasn't change (I'm getting 26 mpg in mixed driving) and it runs OK. I say OK only because there is some rough running in low RPM in hot weather, but otherwise it runs like when I bought it. Like I mentioned, the light comes on intermittently. I've notice if I drive from a big change in altitude, or if I fill up with a different brand of gas, I'll get the light to come on. I also noticed that after an air filter replacement the light stayed off for quite awhile. Based on some of the comments made on the O2 sensors, I think I'll replace those first and see what happens. On May 8, 4:48 pm, mrput...@gmail.com wrote: > > Get your gaskets checked first. > [quoted text clipped - 43 lines] > awhile. Based on some of the comments made on the O2 sensors, I think > I'll replace those first and see what happens. I'll relate my experience with a 2002 Forester, but I am not sure it will shed any light on this phenomena. At about 120000 miles or so, it started throwing 420 CEL codes. I purchased a reader (BR-3: http://obddiagnostics.com/), and, because it was wintertime here in Wisconsin, I simply re-set the code. My reader also allowed me to look at the raw sensor voltage from the sensors, and at times, it seemed the rear sensor had an intermittent connection. I checked the rear sensor connector, but all looked good, but I kept getting CELs (which I would clear) Then, early this year, I purchased a new rear sensor, and replaced the old one with it. Feeling good about myself, I was sad to see the CEL return about 200 miles later, and started to think what my next fix would be. I re-set teh CEL, and kept driving. The car threw maybe 3 or 4 more more, sometime within 50 miles, sometimes after 250 or so, and then it stopped. So far, it has been 5000 miles or so since my last CEL. I do not know if there is any 'burn-in' period for new O2 sensors placed into service, but something happened to make the code go away (for now). I'm not sure there is a definite 'take-away' from my experience, but there it is. Thanks for your time, Duane >On May 8, 4:48 pm, mrput...@gmail.com wrote: >> [quoted text clipped - 78 lines] >Thanks for your time, >Duane Did you change gas brands? Possibly just the change from winter formula gas to summer formula stopped the codes. Some cars are fussy about their fuel quality - I know 2 hondas that throw 420 codes whenever the vehicle is fueled with ESSO (Exxon) gas - and NEVER with Shell. Might have something to do with Ethanol concentration? If so, changing the FRONT O2 sensor may be the fix. A rear sensor problem would be much less likely to cause the 420 code. On May 10, 10:15 pm, cl...@snyder.on.ca wrote: > On Sat, 9 May 2009 05:44:10 -0700 (PDT), DuaneKaufman > [quoted text clipped - 85 lines] > Possibly just the change from winter formula gas to summer formula > stopped the codes. Could be, I suppose. I am not sure how much the gasoline mixes change here in southern Wisconsin for the winter (I do know the diesel sold does). BTW, here we run 10% ethanol pretty much year-round. Then again, one can never proclaim complete victory on a repair, until one gets rid of the car.... > Some cars are fussy about their fuel quality - I know 2 hondas that > throw 420 codes whenever the vehicle is fueled with ESSO (Exxon) gas - > and NEVER with Shell. This 2002 Forester hasn't shown any preference in fuels. > Might have something to do with Ethanol concentration? > If so, changing the FRONT O2 sensor may be the fix. A rear sensor > problem would be much less likely to cause the 420 code. Perhaps. I based my diagnosis (replacing the rear sensor, not the front), on the sporadically erratic rear sensor reading, and the fact that driveability and fuel economy had not changed (thus making me think the front O2 sensor couldn't be too bad) Duane > On May 10, 10:15 pm, cl...@snyder.on.ca wrote: > [quoted text clipped - 116 lines] > > - Show quoted text - I've been dealing with intermittent CEL with code p0420 for about five years on my '00 outback. Between the dealer and my other shop, I think I've been through 5 O2 sensors. I have heard of other people with similar issues resolving it by replacing a leaky y-pipe or y-pipe gaskets. Is there a definitive test of the catalytic converter? > > On May 10, 10:15 pm, cl...@snyder.on.ca wrote: > [quoted text clipped - 125 lines] > > Is there a definitive test of the catalytic converter? A couple of weeks ago, my daughter's forester threw the P0420 code after I had replaced the front O2 sensor. It had thrown a code related to that sensor a couple of weeks before. Since it complained about "efficiency ratio", first replaced the rear O2 sensor, figuring that maybe the rear O2 sensor was reading something it shouldn't, but the 0420 code came back. Since she had to pass emissions before the 17th to re-register, we bit the bullet and changed the CAT two days ago. The light stayed off and it was ready for emission testing yesterday. It passed the test today. > > > On May 10, 10:15 pm, cl...@snyder.on.ca wrote: > [quoted text clipped - 136 lines] > The light stayed off and it was ready for emission testing yesterday. > It passed the test today. Just to add this: The front O2 sensor was definitely bad. It ran very rich causing it to idle badly. After I replaced the front O2 sensor, the mileage was again what it should be. Her car clearly had two problems, with the cat being bad as well. It may have had a leak or something, causing the P0420 code. It is hard to see with all the heat shields in place. >>>> On May 10, 10:15 pm, cl...@snyder.on.ca wrote: >>>>>> On May 8, 4:48 pm, mrput...@gmail.com wrote: [quoted text clipped - 111 lines] > It may have had a leak or something, causing the P0420 code. It is > hard to see with all the heat shields in place. If it had been running rich for a 'significant' amount of time, that is very bad for converters. Add general age/condition issues and I would not be surprised if 2 or all 3 components were bad/compromised. Carl > >>>> On May 10, 10:15 pm, cl...@snyder.on.ca wrote: > >>>>>> On May 8, 4:48 pm, mrput...@gmail.com wrote: [quoted text clipped - 117 lines] > > Carl That's what I figured as well. The O2 sensors were the easiest to replace so did them first. > > >>>> On May 10, 10:15 pm, cl...@snyder.on.ca wrote: > > >>>>>> On May 8, 4:48 pm, mrput...@gmail.com wrote: [quoted text clipped - 120 lines] > That's what I figured as well. The O2 sensors were the easiest to > replace so did them first. Well, here it is two weeks later and the P0420 code is back. At least it passed emissions. Both O2 sensors and the CAT have been replaced. >Well, here it is two weeks later and the P0420 code is back. At least >it passed emissions. >Both O2 sensors and the CAT have been replaced. Factory or aftermarket parts????? If aftermarket all bets are off - period. The replacement parts market is so full of CRAP today that you can easily cause more problems than you fix by installing new parts. On May 25, 10:39 pm, cl...@snyder.on.ca wrote: > >Well, here it is two weeks later and the P0420 code is back. At least > >it passed emissions. [quoted text clipped - 4 lines] > The replacement parts market is so full of CRAP today that you can > easily cause more problems than you fix by installing new parts. Yeah, I heard about those issues so replaced them with genuine Subaru parts.. Maybe I should have gone with aftermarket.. >>>>>>> On May 10, 10:15 pm, cl...@snyder.on.ca wrote: >>>>>>>>> On May 8, 4:48 pm, mrput...@gmail.com wrote: [quoted text clipped - 119 lines] > it passed emissions. > Both O2 sensors and the CAT have been replaced. I know there are cheap aftermarket cats. And some folks have reported problems with using Bosch sensors. But I can't help wondering if there could be another issue. I suppose the wiring is good? Are there any other codes stored? carl > >>>>>>> On May 10, 10:15 pm, cl...@snyder.on.ca wrote: > >>>>>>>>> On May 8, 4:48 pm, mrput...@gmail.com wrote: [quoted text clipped - 126 lines] > > carl I checked the wiring. It looks good. I also checked the snug-ness of the sensors, thinking I didn't tighten it enough. It is good. For that thing to throw a efficiency code, one would imagine that it measures both O2 sensors and, by way of the ratio of one measurement over the other, it decides that the ratio is good/not good. Googling around, it appears some people have put resistors in place of the sensors to get rid of the condition. I wonder if you can pass emissions with them things in place. Don't they measure the O2 sensor's output when they test your emissions? >>>>>>>>> On May 10, 10:15 pm, cl...@snyder.on.ca wrote: >>>>>>>>>>> On May 8, 4:48 pm, mrput...@gmail.com wrote: [quoted text clipped - 134 lines] > emissions with them things in place. Don't they measure the O2 > sensor's output when they test your emissions? If you dig around at www.nasioc.com , you can find out about the resistors and, IIRC, a 'spacer' that also helps with the code. I would prefer to fix it 'correctly' myself - unless i was building a track car or something.... Sigh....it's a bummer not knowing why you still get this code. maybe the ECU is bad? good luck Carl > >>>>>>>>> On May 10, 10:15 pm, cl...@snyder.on.ca wrote: > >>>>>>>>>>> On May 8, 4:48 pm, mrput...@gmail.com wrote: [quoted text clipped - 146 lines] > > Carl I'm with you: I prefer to fix things right. Two years from now, should she need to pass emissions again, I'll have to temporarily hack it to get by. >> >>>>>>> On May 10, 10:15 pm, cl...@snyder.on.ca wrote: >> >>>>>>>>> On May 8, 4:48 pm, mrput...@gmail.com wrote: [quoted text clipped - 136 lines] >emissions with them things in place. Don't they measure the O2 >sensor's output when they test your emissions? A resistor will not do it. The front sensor acts like a battery, with higher oxygen content giving a higher voltage. It has to swing high and low from the .45 volt center. If it doesn't, the system cannot correct mixture and it throws a code. To make the cat work properly it NEEDS to transition from rich to lean. If it never goes rich the one part of the cat will not work. If it never goes lean the other part will not work. The rear sensor monitors the converter. Ideally it will NOT follow the front sensor at all because the converter in an ideal world would even out the O2 level of the exhaust. If the converter is not working properly the rear sensor transitions more - and if it is not working at all it will follow the front sensor exactly. Up hear in Ontario if the CEL is on it doesn't pass - and with a resistor the CEL would come on. Other than that the PCM is not queried - but if the cat is not working up to snuff it won't pass anyway, so it is a moot point. On May 27, 10:00 pm, cl...@snyder.on.ca wrote: > >> >>>>>>> On May 10, 10:15 pm, cl...@snyder.on.ca wrote: > >> >>>>>>>>> On May 8, 4:48 pm, mrput...@gmail.com wrote: [quoted text clipped - 149 lines] > > read more » I only mentioned that people have gotten by hacking it up with some sort of resistor circuitry. Note I'm not suggesting it as a fix. It is disconcerting that it spews a vague error like that. It implies that it has to do with the efficiency of the cat so either it is due to the way the cat's efficiency is monitored or the cat itself. In my case, I've replaced all those components, yet the error comes back like a boomerang. Clearly something else can cause this error to be thrown. Of course, the front O2 sensor was indeed bad. It didn't change when the car was driven. >On May 27, 10:00 pm, cl...@snyder.on.ca wrote: >> [quoted text clipped - 165 lines] >Of course, the front O2 sensor was indeed bad. It didn't change when >the car was driven. The sensor being bad isn't the only thing that will make it not "switch". If the engine is too rich, or too lean, or has an exhaust leak ahead of the sensor, it will read as bad. Other possible causes as well. Also, the converter does not need to be BAD to not work. If it never gets lean enough or rich enough to function properly it will fail it's efficiency test.The nasty exhaust leak before the converter can and will do this. On May 28, 4:23 pm, cl...@snyder.on.ca wrote: . > The sensor being bad isn't the only thing that will make it not > "switch". If the engine is too rich, or too lean, or has an exhaust [quoted text clipped - 5 lines] > efficiency test.The nasty exhaust leak before the converter can and > will do this. I'll crawl under the car again and check that out. I didn't see any before but maybe I missed it. Thanks. >> I only mentioned that people have gotten by hacking it up with some >> sort of resistor circuitry. [quoted text clipped - 19 lines] > efficiency test.The nasty exhaust leak before the converter can and > will do this. I don't know if it would throw a code (it usually doesn't), but possibly the engine temp sensor (not the gage/light sender) could be defective. If the sensor reads as "always cold", the mixture would be rich, hot >> lean. Scientific Wild-Assed Guess... > cl...@snyder.on.ca wrote: > >> I only mentioned that people have gotten by hacking it up with some [quoted text clipped - 27 lines] > > Scientific Wild-Assed Guess... I've had that happen to another subie years ago: Not sure if that still holds true with the newer models but certainly the 93 Impreza became very hard to start, when that sensor went bad. >> cl...@snyder.on.ca wrote: >>>> I only mentioned that people have gotten by hacking it up with some [quoted text clipped - 26 lines] > Not sure if that still holds true with the newer models but certainly > the 93 Impreza became very hard to start, when that sensor went bad. Another WAG, are you losing coolant? I think it can quickly destroy the front O2 sensor. Carl > >> cl...@snyder.on.ca wrote: > >>>> I only mentioned that people have gotten by hacking it up with some [quoted text clipped - 31 lines] > > Carl Good thought, Carl, but nope, no problems other than the p0420 code. >> >> cl...@snyder.on.ca wrote: >> >>>> I only mentioned that people have gotten by hacking it up with some [quoted text clipped - 33 lines] > >Good thought, Carl, but nope, no problems other than the p0420 code. Load up the tank with known 0% etanol fuel, and 99.9% sure the p0420 will go away. It is a calibration issue. On Hondas it is a problem and there is a TSB that addresses it - a reflash of the PCM to accept E10 without triggering the CEL. >Just to add this: >The front O2 sensor was definitely bad. It ran very rich causing it to [quoted text clipped - 5 lines] >It may have had a leak or something, causing the P0420 code. It is >hard to see with all the heat shields in place. A bad O2 semsor causing the engine to run rich will often overheat and kill a cat. When the CEL comes on, find the problem and fix it. Usually a lot cheaper that way. I had the 420 code, put in a new rear O2 sensor, and the CEL went away. My mileage also increased from about 26 mpg to about 28 mpg. I passed emissions a week later. Then about another week later the CEL came back. It's been on for two or three weeks now, but I am still getting improved mileage. I guess I need to go get the codes read again. Hopefully the fact that my mileage is still improved means I'm fine and the CEL is for another reason than a 420 code. Hopefully. >I had the 420 code, put in a new rear O2 sensor, and the CEL went >away. My mileage also increased from about 26 mpg to about 28 mpg. I [quoted text clipped - 3 lines] >again. Hopefully the fact that my mileage is still improved means I'm >fine and the CEL is for another reason than a 420 code. Hopefully. Sorry to burst your bubble, but a rear O2 sensor is a monitor only and can not affect your gas mileage - period. ANd as stated before, a 420 code will not be solved by replacing a rear sensor alone. The front sensor is more likely to be the culprit - or an actual bad cat. (which would generally not pass e-test) > Sorry to burst your bubble, but a rear O2 sensor is a monitor only and > can not affect your gas mileage - period. went through a incredible class a few years ago concerning rear 02 sensors and fuel trim. Even tho the manufactured say it won't, or in some cases will say "minorly" it can major effect fuel trim/gas mileage. its the difference in what the tell you, and "us" the manufacture tech's and what really happens. Steve >> Sorry to burst your bubble, but a rear O2 sensor is a monitor only and >> can not affect your gas mileage - period. [quoted text clipped - 5 lines] >what really happens. >Steve Explain how the catalyst monitor affects fuel mileage. I'm all ears. >>> Sorry to burst your bubble, but a rear O2 sensor is a monitor only and >>> can not affect your gas mileage - period. [quoted text clipped - 9 lines] >> > Explain how the catalyst monitor affects fuel mileage. I'm all ears. LOL, I'll see if I can find the original post. Here it is, I cut some of the non applicable stuff. CTI Book Page 104 (CarQuest technical Institute) ... What is the purpose of the post cat Oxygen sensor? --Catalyst efficiency monitor? That's only a portion of its function REAR FUEL TRIM a.. The Post-cat O2S has been used since 1988 to control fuel trim (to some extent) a.. Toyota and Saab b.. Used to fine-tune the A/F ratio to maximize catalyst efficiency c.. Will also compensate for a degraded Catalyst d.. Every manufacture today uses the rear O2S to trim fuel today The post cat O2S is a fuel control input. Toyota and Saab have used the post-cat O2 to control the fuel trim since 1988; Before OBD-II. This sensor is used to fine-tune the air-fuel ratio to maximize catalyst efficiency. It can also adjust the air fuel ratio to compensate for a degraded Catalyst. If you were to measure the actual amount of time the post-cat O2 is used during the running of the catalyst monitor (maybe once per trip) and compare that to the amount of time the post-cat O2 is used fine tune the air-fuel ratio (almost always in closed loop), you will see that this sensors major function is fuel control. Every vehicle manufacture today uses the rear O2S for fuel correction; even if it is undocumented. a.. How much control over fuel trim does the rear O2S have? a.. GM material says less than 1.0% b.. Ford says 0.5% c.. Toyota says 2.0% d.. Under normal conditions b.. We have seen up to 30% correction in fuel trim from the rear O2S in abnormal conditions (SNIP) According to these manufactures, the post-cat oxygen sensor has minimal control over fuel trim under normal operating conditions. GM material states the rear O2S has +/-1.0% authority over fuel control. The Ford OBD-II manual leads us to believe this sensor is of little consequences in regard to drivability as it only has +/-0.5 fuel control authority. Toyota allows for a whopping 2.0% +/- correction. However these claims are under normal driving circumstances. What happens if there is a problem? We have documented up to 30% correction in fuel trim from the rear O2S in abnormal conditions. (SNIP) Rear fuel trim Experiment The Guinea pig; 1999 Dodge Grand Caravan Sport. 3.3 Vin G. 168000 miles We wanted to determine what, if any, input the rear O2 sensor has on fuel trim. Many vehicles have rear fuel trim PIDs available. Some OEMs have even documented the range in which the rear O2 can affect total fuel trim. On this vehicle however, Chrysler specifically states that the sole function of the rear O2 is for the catalyst monitor. Period! The rear O2 sensor has zero input on fuel control. The idea behind this experiment is to control the rear O2 sensor voltage to the minimum and maximum extreme of normal values for an extended period of time and monitor short term and long term PIDs on the scan tool. The rear O2 voltage will be controlled with a sensor simulator. (Snip) Steve abbreviates: a.. Drive 1 Normal conditions a.. B1S1 Switching 100MV and 900MV b.. B1S2 steady at 600MV c.. Fuel trim a.. Shot term FT +4%-4% b.. Long term +3% Drive 2 The sensor is set to 120 MV, low end of the range B1S1 O2s is stuck full rich; except for the few times the engine experienced slight misfires due to the over-rich condition. Short-term fuel trim has apparently reached its limit at +25%. Long term stopped at +22% Since STFT is fairly fixed its easy (to calculate the total fuel trim) +47%! NO CONFERMED DTC' WERE SET! We do have the following pending DTCs: P0172 Fuel system rich B1S1; P0170 Fuel trim fault B1S1. Notice the PCM is ignoring the B1S1 O2S because it is attempting to optimize the catalyst. This is the PCMs priority (Note MPG went from 20 MPG to 15) Drive 3 Thee sensor is set to 850 MV, the high end of the range B1S1 O2s is stuck dead lean; Ran fine (but couldn't climb a hill) Short-term fuel trim has apparently reached its limit at -20%. Long term stopped at -25% Since STFT is fairly fixed its easy (to calculate the total fuel trim) +47%! Once again NO CONFERMED DTC' SET! We do have the following pending DTCs: P0171 Fuel system lean B1S1; P0170 Fuel trim fault B1S1; P0131, B1S1 Shorted to ground. Note the codes do not tell your anything about the rear o2 sensor? (Note MPG went from 20 MPG to 25) Anyway, that sums up the first case; I had to abbreviate some stuff (pictures and graphs and stuff) but it gives you something to think on. There is another case about a Ford escape; perhaps someday I'll type it up. >>>> Sorry to burst your bubble, but a rear O2 sensor is a monitor only and >>>> can not affect your gas mileage - period. [quoted text clipped - 17 lines] > > REAR FUEL TRIM ... > Every vehicle manufacture today uses the rear O2S for fuel > correction; even if it is undocumented. Ohhhh snap. -- Todd H. 2001 Legacy Outback Wagon, 2.5L H-4 Chicago, Illinois USA >>>> Sorry to burst your bubble, but a rear O2 sensor is a monitor only and >>>> can not affect your gas mileage - period. [quoted text clipped - 41 lines] >function is fuel control. Every vehicle manufacture today uses the rear O2S >for fuel correction; even if it is undocumented. I'd question the "every vehicle" Also, the "abnormal conditions" may have included some other malfunction??? 2% is 1/4 mpg at 25 mpg mean. and I'd grant you that might be normal (and also virtually undetectable to the average driver/owner, and even mechanic.) > I'd question the "every vehicle" > [quoted text clipped - 4 lines] > (and also virtually undetectable to the average driver/owner, and even > mechanic.) This is what the class was about. using fuel trim to analyze the car. This class was in late 2005. At this time Ford's scantool was the only one that was offering a pid for "rear fuel trim" and using that info the class did a case study on a car that had excessive fuel consumption. the Ford shop looked at it twice, and using standard diag techniques it read OK (Short term+long term= indication of fuel consumption) said it was OK. But, by adding in the rear fuel trim numbers suddenly the car was not OK. Ended up having excessive alcohol in the fuel. I honestly think all card use this, but don't document it even now. >> I'd question the "every vehicle" >> [quoted text clipped - 14 lines] >having excessive alcohol in the fuel. >I honestly think all card use this, but don't document it even now. It was the excess alcohol that made the rear sensor come into play, i'd venture to bet. Running E85 in a non-flex-fuel engine can cause all kinds of anomolies. Under normal operating conditions a rear O2 sensor has very minimal mixture authority - and I believe that is dictated by the OBD2 standard. >>> Sorry to burst your bubble, but a rear O2 sensor is a monitor only and >>> can not affect your gas mileage - period. [quoted text clipped - 7 lines] >> > Explain how the catalyst monitor affects fuel mileage. I'm all ears. Maybe the monitoring actually is used as an input to the ECU that does something with fuel trim on his particular model and year? Theory or not, we have one person on the thread write "I had the 420 code, put in a new rear O2 sensor, and the CEL went away. My mileage also increased from about 26 mpg to about 28 mpg." and another indicating having learned that there's anecodotal evidence that suggests this can actually happen. On the other hand, you're swearing up and down that changing a rear O2 can't possibly be causally linked to a change in fuel economy. I'm not sure the burden of proof is on the others. Now, maybe you are omniscient on the topic and know for a fact that every design of his model, year and engine has a rear O2 that does NOTHING to adjust any parameters that'd affect fuel economy, and the other two data points are invalid. But my reading on the subject suggests that the rear O2 does affect air fuel mixture, just not nearly as directly as the front does. -- Todd H. 2001 Legacy Outback Wagon, 2.5L H-4 Chicago, Illinois USA >>>> Sorry to burst your bubble, but a rear O2 sensor is a monitor only and >>>> can not affect your gas mileage - period. [quoted text clipped - 29 lines] >But my reading on the subject suggests that the rear O2 does affect >air fuel mixture, just not nearly as directly as the front does. From what I had read previously, those pre-obd2 vehicles that used secondary O2 sensors could use them for fuel trim to optimize the cat, but it was my understanding the OBD2 standard did not "allow" this. However, it is becoming obvious nobody adheres to "standards" You'd think we were talking about the computer industry - - - > From what I had read previously, those pre-obd2 vehicles that used > secondary O2 sensors could use them for fuel trim to optimize the cat, > but it was my understanding the OBD2 standard did not "allow" this. > However, it is becoming obvious nobody adheres to "standards" > > You'd think we were talking about the computer industry - - - Think the other way when it comes to OBD standards. The Manufactures can do whatever they want in there cars as long as certain conditions are met. Emissions to a certain level. Usually modeling after California's standards that are higher than the rest of the world. Certain Info available to the general shop; The EPA and all the biggie-wigs in Washington decide what Pids are available to the aftermarket world, OBD Generic. IE, several years ago Misfire Data wasn't available except on OEM scanners, now it is more common on the generic lines. IF a manufacture decided to give more info to the aftermarket world, they could. A prime example was Chrysler. They had ton's more info available on a aftermarket scanners years before other car manufactures. Even though OBD is a rule, interpretation of the rules vary by manufacture. The 1996 rules for the obd data plug said something along the line of "Must be located 12" from the centerline of the dash, visible by the technician from the drivers door area". How can hidden under a ashtray be classified as "Visible" (Honda) Some were on the passenger side of the dash. The rules are up for grabs. >I have heard of other people with similar issues resolving it by >replacing a leaky y-pipe or y-pipe gaskets. > >Is there a definitive test of the catalytic converter? If you have a leak ahead of the converter you WILL have troubles. Fix all leaks first. A good indication of whether a cat is working is to check temperature at the front of the converter and at the back. The back should be hotter. > My ’01 Forester with 78k miles is getting an intermittent CEL. Had it > in the shop for routine oil change and the code is pointing to the [quoted text clipped - 5 lines] > Magnaflow, Catco, DEC, and Eastern. Anyone have any experience, good > or bad, with non OEM replacements? Clear the code. If only one comes back, definitely try changing the front O2 sensor. 78K would be early for a cat to go bad on a 'typical' car. But not too early for an O2 sensor. order of magnitude difference in price. Still, a GOOD shop should be able to scope the sensor and , if good, flow test or tailpipe test for a bad cat. I suspect your dealer would change both but 'say' the cat was bad. I 'might' be tempted to get a second opinion anyway. Many people have had (is it 420?) cat efficiency codes/w'ever and changed the sensor and been OK for another 80,000 miles. Do get the Subaru sensor though. Some folks have had problems with aftermarket units. Carl >> My ’01 Forester with 78k miles is getting an intermittent CEL. Had it >> in the shop for routine oil change and the code is pointing to the [quoted text clipped - 18 lines] > > Carl I agree. When my car was upgraded to a Stage 2, a high flow cat was part of the package (aftermarket). It required a software upgrade to recalibrate the cat efficiency and defeat the P0420 code. Many aftermarket cats and sensors will cause it to be thrown. |
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