Toyota Tacoma P0420 cat or o2 sensor
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From: jcaru on 14 Apr 2007 14:32 I have a 2000 Toyota Tacoma TRD 3.4 liter with california emissions and 114,500 mile.P0420 catalyst efficiency below threshold (bank1) came up on OBDII scanner. My gas mileage seemed to have dropped about 3-4 miles per gallon since check engine light came on. I replaced the o2 sensor after the two cats a couple years back. From the reading I have done and people I've talked to it seems my cat maybe clogged. If I replace the cat with a High Flow cat (MagnaFlow) will it cause problems with my sensors. And also can I do anything about getting rid of one of the cats since I live in Pa and have no intentions of going to Cal. What is the best thing to do to fix this problem. Dealer price for front and rear cat are $940 and $1045 (not an option). Thanks in advance for all replies. -Jason
From: Jeff Strickland on 14 Apr 2007 15:20 My inclination is to focus on the sensor before the CAT itself. In my world, the CAT is very reliable, and if it were to phsically clog, there would be driveability issue that you would notice before the computer told you there was a problem. Surely I'll face argument here, but I have solid reasoning. If the CAT were to clog, then the flow would diminish, causing a loss of intake. You would feel the loss of intake. The sensor that decides efficiency is not looking at the flow, it's looking at the residual fuel content. The exhaust stream ahead of the CAT contains stuff that the sensor after the CAT does not want to see. If the CAT is properly converting the exhaust stream gasses, then the sensor is happy. If the sensor is not happy, the computer does not know if the sensor itself is toast or if the CAT is toast, but the display is the same. It is certainly possible for the CAT to be toast, but I place my pile of poker ships on the sensor first. RayO, here, will be able to give a test -- one that I ought to know how to perform, but my guess at the sensor has always been correct so I haven't ever done the test that Ray knows. There are O2 Sensors ahead of the CAT too, but there are codes that will tell you if they (or it, if there is only one) is not functioning properly. Having said that, Ray's testing procedure will help you isolate the offending sensor so you replace the proper part. "jcaru" <Jason.Caruso(a)gmail.com> wrote in message news:1176575524.813977.243550(a)y80g2000hsf.googlegroups.com... >I have a 2000 Toyota Tacoma TRD 3.4 liter with california emissions > and 114,500 mile.P0420 catalyst efficiency below threshold (bank1) > came up on OBDII scanner. My gas mileage seemed to have dropped about > 3-4 miles per gallon since check engine light came on. I replaced the > o2 sensor after the two cats a couple years back. From the reading I > have done and people I've talked to it seems my cat maybe clogged. If > I replace the cat with a High Flow cat (MagnaFlow) will it cause > problems with my sensors. And also can I do anything about getting rid > of one of the cats since I live in Pa and have no intentions of going > to Cal. What is the best thing to do to fix this problem. Dealer price > for front and rear cat are $940 and $1045 (not an option). > > Thanks in advance for all replies. > -Jason >
From: al on 14 Apr 2007 21:08 On Apr 14, 2:32 pm, "jcaru" <Jason.Car...(a)gmail.com> wrote: > I have a 2000 Toyota Tacoma TRD 3.4 liter with california emissions > and 114,500 mile.P0420 catalyst efficiency below threshold (bank1) > came up on OBDII scanner. My gas mileage seemed to have dropped about > 3-4 miles per gallon since check engine light came on. I replaced the > o2 sensor after the two cats a couple years back. From the reading I > have done and people I've talked to it seems my cat maybe clogged. If > I replace the cat with a High Flow cat (MagnaFlow) will it cause > problems with my sensors. And also can I do anything about getting rid > of one of the cats since I live in Pa and have no intentions of going > to Cal. What is the best thing to do to fix this problem. Dealer price > for front and rear cat are $940 and $1045 (not an option). > > Thanks in advance for all replies. > -Jason I'd definitely suspect the front O2 sensor before condemning the cat. The drop in gas mileage is another strong indicator of a lazy O2 sensor. The front O2 sensor monitors the oxygen content of the exhaust gas in the manifold and should normally be switching rapidly between about 200 millivolts and 800 mv as the computer rapidly adjusts the fuel/air ratio to optimize the fuel mixture. If the cat is working properly, the rear O2 sensor should output a fairly constant voltage of about 450mv. The computer compares the switching rate of the front O2 sensor to that of the rear O2 sensor. If the switching rates are similiar, it sets the P0420 code under the theory that the exhaust gas coming out of the cat looks very similiar to exhaust gas going into the cat and so the catalyst efficienct is below normal. But if the front O2 sensor gets lazy and starts switching too slowly, then the P0420 code is set and the problem is the sensor and not the cat. It is also possible that the front O2 sensor heater circuit is malfunctioning which would cause the O2 sensor to not get hot enough, especially at idle, to work properly. However, if that were true, there is usually a separate code for that. Before spending a ton of money on a cat, it would be very worthwhile to put the vehicle on a scan tool and watch the operation of the O2 sensors and observe that the O2 heaters are on. If you can't do that, investing in a $50-75 OEM front O2 sensor first before opting for the $1000 fix would seem to make good economic sense. Good luck. Al
From: Paul. on 16 Apr 2007 21:04 Or, if you still have the old O2 sensor, take the new one and put it in front of the cat and put the old one back in the rear position. It's cheap if you still have the old part. Paul. "al" <abuonag(a)msn.com> wrote in message news:1176599284.186758.241300(a)n76g2000hsh.googlegroups.com... > On Apr 14, 2:32 pm, "jcaru" <Jason.Car...(a)gmail.com> wrote: >> I have a 2000 Toyota Tacoma TRD 3.4 liter with california emissions >> and 114,500 mile.P0420 catalyst efficiency below threshold (bank1) >> came up on OBDII scanner. My gas mileage seemed to have dropped about >> 3-4 miles per gallon since check engine light came on. I replaced the >> o2 sensor after the two cats a couple years back. From the reading I >> have done and people I've talked to it seems my cat maybe clogged. If >> I replace the cat with a High Flow cat (MagnaFlow) will it cause >> problems with my sensors. And also can I do anything about getting rid >> of one of the cats since I live in Pa and have no intentions of going >> to Cal. What is the best thing to do to fix this problem. Dealer price >> for front and rear cat are $940 and $1045 (not an option). >> >> Thanks in advance for all replies. >> -Jason > > I'd definitely suspect the front O2 sensor before condemning the cat. > The drop in gas mileage is another strong indicator of a lazy O2 > sensor. The front O2 sensor monitors the oxygen content of the > exhaust gas in the manifold and should normally be switching rapidly > between about 200 millivolts and 800 mv as the computer rapidly > adjusts the fuel/air ratio to optimize the fuel mixture. If the cat > is working properly, the rear O2 sensor should output a fairly > constant voltage of about 450mv. The computer compares the switching > rate of the front O2 sensor to that of the rear O2 sensor. If the > switching rates are similiar, it sets the P0420 code under the theory > that the exhaust gas coming out of the cat looks very similiar to > exhaust gas going into the cat and so the catalyst efficienct is below > normal. But if the front O2 sensor gets lazy and starts switching too > slowly, then the P0420 code is set and the problem is the sensor and > not the cat. It is also possible that the front O2 sensor heater > circuit is malfunctioning which would cause the O2 sensor to not get > hot enough, especially at idle, to work properly. However, if that > were true, there is usually a separate code for that. Before spending > a ton of money on a cat, it would be very worthwhile to put the > vehicle on a scan tool and watch the operation of the O2 sensors and > observe that the O2 heaters are on. If you can't do that, investing > in a $50-75 OEM front O2 sensor first before opting for the $1000 fix > would seem to make good economic sense. Good luck. Al >
From: jcaru on 16 Apr 2007 22:26
On Apr 16, 9:04 pm, "Paul." <paul.blomb...(a)cox.net> wrote: > Or, if you still have the old O2 sensor, take the new one and put it in > front of the cat and put the old one back in the rear position. > > It's cheap if you still have the old part. > > Paul."al" <abuo...(a)msn.com> wrote in message > > news:1176599284.186758.241300(a)n76g2000hsh.googlegroups.com... > > > On Apr 14, 2:32 pm, "jcaru" <Jason.Car...(a)gmail.com> wrote: > >> I have a 2000ToyotaTacomaTRD 3.4 liter with california emissions > >> and 114,500 mile.P0420 catalyst efficiency below threshold (bank1) > >> came up on OBDII scanner. My gas mileage seemed to have dropped about > >> 3-4 miles per gallon since check engine light came on. I replaced the > >> o2 sensor after the two cats a couple years back. From the reading I > >> have done and people I've talked to it seems my cat maybe clogged. If > >> I replace the cat with a High Flow cat (MagnaFlow) will it cause > >> problems with my sensors. And also can I do anything about getting rid > >> of one of the cats since I live in Pa and have no intentions of going > >> to Cal. What is the best thing to do to fix this problem. Dealer price > >> for front and rear cat are $940 and $1045 (not an option). > > >> Thanks in advance for all replies. > >> -Jason > > > I'd definitely suspect the front O2 sensor before condemning the cat. > > The drop in gas mileage is another strong indicator of a lazy O2 > > sensor. The front O2 sensor monitors the oxygen content of the > > exhaust gas in the manifold and should normally be switching rapidly > > between about 200 millivolts and 800 mv as the computer rapidly > > adjusts the fuel/air ratio to optimize the fuel mixture. If the cat > > is working properly, the rear O2 sensor should output a fairly > > constant voltage of about 450mv. The computer compares the switching > > rate of the front O2 sensor to that of the rear O2 sensor. If the > > switching rates are similiar, it sets theP0420code under the theory > > that the exhaust gas coming out of the cat looks very similiar to > > exhaust gas going into the cat and so the catalyst efficienct is below > > normal. But if the front O2 sensor gets lazy and starts switching too > > slowly, then theP0420code is set and the problem is the sensor and > > not the cat. It is also possible that the front O2 sensor heater > > circuit is malfunctioning which would cause the O2 sensor to not get > > hot enough, especially at idle, to work properly. However, if that > > were true, there is usually a separate code for that. Before spending > > a ton of money on a cat, it would be very worthwhile to put the > > vehicle on a scan tool and watch the operation of the O2 sensors and > > observe that the O2 heaters are on. If you can't do that, investing > > in a $50-75 OEM front O2 sensor first before opting for the $1000 fix > > would seem to make good economic sense. Good luck. Al Thanks for all the input. I have a good mechanic that will help the truck pass emissions if you know what I mean. Say it is the front 02 sensor. Will and after market Cat mess with my sensors at all. And also how do I place the voltmeter on the sensor to test them?? |