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  • avatar zaken1 06/06/10 3:29 pm PST

    There are two different types of problems which will cause a catalytic converter code to set. One could happen if the converter was plugged up. That is easy to check yourself; with no experience or tools required. Just walk over to the end of the exhaust pipe and have someone sit in the car and press hard on the accelerator. When the accelerator is pressed hard; there should be a blast of exhaust coming out of the pipe, along with a corresponding increase in exhaust noise. If that happens; the converter is not plugged up. If the converter is plugged; there will be little or no change in the amount of exhaust or sound level coming from the pipe when the pedal is pressed. If the converter passes this test; it probably does not need to be replaced.

    The second cause for a converter code to set is if there is little difference between the readings from the O2 sensor before the cat and the one after the cat. That is called a catalytic converter efficiency measurement. A converter that is in good condition will burn up a lot of the pollutants that come out of the motor. When that takes place; there will be a big difference between the chemical composition of the exhaust before and after the converter; and that difference will be shown in a corresponding difference between the two O2 sensor readings. If there is little or no difference between the O2 sensor readings; it is either caused by a catalitic converter that is not doing anything; or by a bad O2 sensor. At the current mileage on this car, it is far more likely that an O2 sensor is bad than a converter being bad. Since you've already replaced the front O2 sensor; you're already halfway there. The one you already replaced is certainly not going to be bad now. So all you need to do is to have the rear O2 sensor replaced. Yes, it will cost some bucks; but you can also raise the selling price of the car to cover a portion of that cost; as new O2 sensors are value added to the car.

    And this is the proper way to deal with this situation.


    It is possible to test an O2 sensor before replacing it. The test must be done on the car, and involves measuring the sensor output voltage with the engine running on different levels of richness in the fuel mixture. The mixture can be externally richened by pouring some gasoline or spraying propane into the air intake while the motor is running. There is a major fire risk when doing this; so it is not recommended for unskilled people, or for people who smoke when they work on cars or do not have a fire extinguisher handy. The sensor voltage should increase significantly when the mixture is enriched. If it doesn't change much or at all; the sensor is bad. It will be up to you to decide whether the cost of labor for testing the rear sensor is worth paying; compared to the cost and time and hassle saved by just buying and installing a new one.

Answers

  • morin2 06/06/10 1:11 pm PST

    Not only is a temporary fix just long enough to dump this on an unsuspecting buyer higher unethical, it may also come back to haunt you, regardless of how you attempt to couch the sale with "as is" receipt. What you propose is a good reason why used car buyers should always have a pre-purchase inspection performed by a mechanic.

    Always follow the golden rule and disclose everything. This car is a candidate for trading in to a dealer (with disclosure there too) because the dealer will not be emotionally involved in the purchase - its just a business decision.

    Put yourself in the buyer's shoes. Would you appreciate someone doing this to you?

  • MrShift@Edmunds 06/06/10 1:14 pm PST

    What code # are you getting. I think "do onto others" applies here, not sticking the next buyer with your problem two days after he buys your car. You may have 2 sensors if you have the 2.0L engine. Chances of your cat being wiped out at 90K aren't that likely.

    This problem needs more diagnostics and thought then you are giving it.

    But to answer the question, no, there is no way to fix a plugged cat---but if your cat was plugged up, your car would run very badly.


  • avaisnor624 06/06/10 1:29 pm PST

    I'm not trying to put this onto someone else. I'm not asking for a two day fix, more like a one year fix. Someone buying a 2003 Jetta should know that there are going to be problems and I would be disclosing all information. I just can't afford to buy a brand new Catalytic Converter so even if I was keeping the car I would look for other solutions. I've also read that sometimes a diagnostic reading can say it's the cat when in fact it's just the other sensor. So if someone can give me a helpful solution instead an accusation, that would be appreciated. I know there is more than one way to fix this problem. How about something to clean out the cat so it produces cleaner emissions and doesn't need to be replaced?
    Per the second answer, I'm not sure about the code since a mechanic did it for me, but i do have the 2.0 version and i did readthat having a crapped out cat this ealry on is unlikely...I heard that the dealership must replace it if it's under warrenty...is that accurate? If someone could please help me with some other options besides calling me unethical, that would be nice. I am an honest college student and I'm not going to sell someone a car that i "sneakily" temporarliy fixed right before they buy it..I'm just looking for how I can fix the problems without shelling out thousands more because I've already done that. My question before may have been misleading, so I apologize for that.
    So I guess my new question is, if it's not the cat even though the diagnotic test said it was, what could it be? I'veseriously spent a lot of time on this. I've been to 3 mechanics, replaced the vaccum hose, the bank 1 o2 sensor, my boyfriend has looked at it several times and discussed this with several mechanic buddies, and I spend an hour at auto zone with an employee trying to get hlp. I'm a 22yr old girl so I've doneas much as someone with littlecar experience can do. Help!!!

  • isellhondas 06/06/10 1:54 pm PST

    It almost sounds like you are in denial over the catalytic convertor being bad?

    It is what it is unfortunatly.

    Maybe you can find a used one off a low mileage wreck in a wrecking yeard somewhere?

  • MrShift@Edmunds 06/06/10 1:59 pm PST

    No you are unfortunately over the limit for the Federal Emissions Warranty which is 80,000 miles or 8 years, whichever comes first.

    I don't think there's much we can do for you without the trouble code #. Autozone should be able to retrieve this for you for free. I also don't understand how 3 mechanics can't get you through a smog check. But you know, some problems do take some hard detective work, so the mechanic has to be smart AND motivated; otherwise, they'll just tell you to throw parts at it until the light goes off. On your end, you have to be willing to pay for the diagnostic time. Sometimes, owners figure "I'll just replace parts rather than pay for diagnostic labor--it might be cheaper", and sometimes that strategy works---but if it doesn't you've throw a lot of money away.

    Anyway, an oxygen sensor can be tested. If they replaced one and it didn't solve the problem then they didn't test it. Lazy? Dunno.

    A car's computer doesn't tell you which part is defective. No computer can do that. All it does it tell you which circuit or system is reporting trouble. Reading the code is just Step 1. Step 2 is diagnosis, not parts replacement. Parts replacement is Step 3.

    Hope all this helps you plan a better strategy for this frustrating problem.




  • avaisnor624 06/06/10 1:59 pm PST

    I just think my car is too new to have the catalytic converter go bad. when I did some research, I read that a diagnostic reading can say it's thecat when it's actually thesensor so that's what I'm wondering. I replaced the sensor before the cat but not the post-cat sensor. I just want to explore my options before shelling out $360 for a new cat or even $150 for a second sensor. Also, the previous answer said the car should be making a lot of noise if the cat went bad, but it's not making any weird noises so I'm just not entirely sure, if that makes any sense.

  • avaisnor624 06/06/10 2:15 pm PST

    I'm not sure what you mean by "diagnostic labor"...do you mean looking at all the possible porblems before replacing the parts? Also, can they test the oxygen tester before it's replaced? For example, testing the second one to make sure it's that and not the cat before I replace it? I live in California and AutoZone's here don't check code numbers anymore; they stopped 2 years ago. You have to buy the code scanner yourself now or go to a mechanic. Lastly, my boyfriend replaced the sensor and I went to a mechanic to have the computer reset so the light would turn off because I thought the sensor was the only problem. it turned off for about 5 dayd and then turned back on, this time saying it's either thesenor or the cat but it coudnt tell me which sensor - I guess that was my first mistake. So it's either the one i replaced or the one I didn't.

  • zaken1 06/06/10 3:29 pm PST

    There are two different types of problems which will cause a catalytic converter code to set. One could happen if the converter was plugged up. That is easy to check yourself; with no experience or tools required. Just walk over to the end of the exhaust pipe and have someone sit in the car and press hard on the accelerator. When the accelerator is pressed hard; there should be a blast of exhaust coming out of the pipe, along with a corresponding increase in exhaust noise. If that happens; the converter is not plugged up. If the converter is plugged; there will be little or no change in the amount of exhaust or sound level coming from the pipe when the pedal is pressed. If the converter passes this test; it probably does not need to be replaced.

    The second cause for a converter code to set is if there is little difference between the readings from the O2 sensor before the cat and the one after the cat. That is called a catalytic converter efficiency measurement. A converter that is in good condition will burn up a lot of the pollutants that come out of the motor. When that takes place; there will be a big difference between the chemical composition of the exhaust before and after the converter; and that difference will be shown in a corresponding difference between the two O2 sensor readings. If there is little or no difference between the O2 sensor readings; it is either caused by a catalitic converter that is not doing anything; or by a bad O2 sensor. At the current mileage on this car, it is far more likely that an O2 sensor is bad than a converter being bad. Since you've already replaced the front O2 sensor; you're already halfway there. The one you already replaced is certainly not going to be bad now. So all you need to do is to have the rear O2 sensor replaced. Yes, it will cost some bucks; but you can also raise the selling price of the car to cover a portion of that cost; as new O2 sensors are value added to the car.

    And this is the proper way to deal with this situation.


    It is possible to test an O2 sensor before replacing it. The test must be done on the car, and involves measuring the sensor output voltage with the engine running on different levels of richness in the fuel mixture. The mixture can be externally richened by pouring some gasoline or spraying propane into the air intake while the motor is running. There is a major fire risk when doing this; so it is not recommended for unskilled people, or for people who smoke when they work on cars or do not have a fire extinguisher handy. The sensor voltage should increase significantly when the mixture is enriched. If it doesn't change much or at all; the sensor is bad. It will be up to you to decide whether the cost of labor for testing the rear sensor is worth paying; compared to the cost and time and hassle saved by just buying and installing a new one.

  • avaisnor624 06/06/10 3:34 pm PST

    How do I read an O2 sensor? and thank you, this was extremely helpful :)

  • zaken1 06/06/10 3:40 pm PST

    Please re-read my previous answer. I revised it to include information on testing sensors while you were posting your response (so they crossed in the mail).

  • MrShift@Edmunds 06/06/10 5:15 pm PST

    A mechanic who knows what he/she is doing, should be the one doing the testing of the 02 sensor. "Diagnostic labor" is the time you pay for while the mechanic is testing your car to see what is wrong--it's not the "fixing" of the car, it's the detective work beforehand.

  • dlugitch 06/08/12 2:34 pm PST

    I have a 1998 Hyundai Tiburon-220K miles. The car ran and continues to run well. I had to smog the vehicle this year and thanks to the NO enchanced test the vehicle failed to pass smog for the first time. I was very skeptical to use lacquer thinner but I didn't want to invest $500-$1000 on a new catalytic convertor. Living IN CA these cost $500+. I changed the oil, new spark plugs (didn't need it) and new plug wire (didn't need it) and then purchased a gallon of lacquer thinner. I drove the car for about 3 hours and put roughly 150 miles on the car and drove it into a smog test-only facility and it passed. The reading was about 250 on the NO2 rather than the 767 that failed it.

    Use Scotty's advise before you spend a dime

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