hi
I have a toyota corolla 2001, with about 140,000 miles on it.
I had replaces O2 sensor (before) and and MAF sensor last year because i was getting P0171 error.
Now i am getting P0420 error, i dont know why. how do i check and make sure which part i need to replace, i am not a expert mechanic, and i tried to talk with a few and they are giving me budget of about 800 to 900 $ to fix it.
Any advice, i live near allentown in PA, does anyone know a good mechanic there who could fix it with reasonable price.
P0420 means inefficient catalyst system, which could mean bad catalytic converter, but this code can also be triggered by bad O2 sensors. On your car, there is 2 oxygen sensors: bank 1 in the front of the catalytic converter and bank 2 at the end of the cat. What bank # does your P0420 code give you? Some scanners tell that, some dont. You can take the car to a Autozone or Pepboys and they'll check it for free.
If the catalytic converter is going bad, you will experience performance problems, for example, sluggish acceleration, trouble going uphill, rotten egg smell through exhaust and rattling sound coming from within cat (sound may not be obvious from inside car, it will have to be checked manually).
First thing I would do is check the voltage on both oxygen sensors to make sure they're working correctly. If they're not, replace them first, but keep your original part. If the code comes back after replacing the sensors, you could put old parts back in and go for the cat.
If it turns out the cat is bad, you can get a aftermarket direct bolt on installed for around $300. They do come with 5 year / 50000 mile warranty, so there is really no point in going for OEM converter which can cost you at least $800 plus installation.
P0420 usually means there is a problem with the 02 (A/F) sensors, their circuits (wiring) or the CAT. The 02 (A/F) sensor signals before and after the CAT are compared by the ECU. This allows determining the efficiency of the CAT. If the signals are the same amplitude, the ECU thinks either the sensors are bad, the circuit or the CAT is operating below efficiency. It does not know specifically which part is bad.
Hi
So how do we figure which part to change, is there a sequence we can follow like for example to say change O2 sensor first and then CAT or vice versa,
What is the cost involved in changing them, and where do i get the required parts
Hi Vikram
I dont get any sluggish performance, i get about 35 miles per gallon on highway and pick up is great,
so how do i check the voltage on oxygen sensor, i have already changed the before O2 sensor,
I have gone to AutoZone and the machine there does not tell which of the O2 sensor is giving this error message.
Do i have to check if my car is using lot more oil (engine oil) how do i measure it acurately
Since you do not have performance problems, more than likely you have bad o2 sensor. You will have to take the car to a pro mechanic to get the o2 sensors checked out. They run about 100 a piece I believe. You could buy a AC DELCO sensor from Napa / Oreilly's instead of from the dealership.
Mechanics love to throw parts at the car because it means money for them, but tell them specifically that you want the voltage checked on the sensors to figure out if they're really bad. Let them know, you already know the codes, so they don't slap $85 for merely telling you its a P0420.
What I have found in the United States is you cant take mechanic's honesty for granted. You gotta push aggresively your views and opinions and make it clear to them that you're not willing to simply throw parts at the car just because they *think* parts may be bad. Make them prove it first. In any case, keep old parts so you can return the new ones if it turns out they were not bad.
Since you do not have performance issues, this problem is not related to oil burning. Do you know if your car is burning oil? Keep checking the dipstick and any smoke from tailpipe (bluish smoke usually means oil burning).
The dealer is able to tell what the problem is because they have a scanner that can dispaly the signals from the sensors. An oscilloscope would do the same thing.
If the car runs well and passes smog, would think it was the sensor (or wiring to them). Best guess is the first sensor which takes the brunt of the oil, gas and whatever else is going by. I have read they might be able to be cleaned but never got into the details (if possible).
Hi
I got it checked by another mechanic and the code is P0420 and it says by Blank 1 #
does this mean any thing?
Ashish
means its the first 02 sensor,
"
Use a high impedance DC voltmeter as above. Clamp the sensor in a vice, or use a plier or vice-grip to hold it. Clamp your negative voltmeter lead to the case, and the positive to the output wire. Use a propane torch set to high and the inner blue flame tip to heat the fluted or perforated area of the sensor. You should see a DC voltage of at least 0.6 within 20 seconds. If not, most likely cause is open circuit internally or lead fouling. If OK so far, remove from flame. You should see a drop to under 0.1 volt within 4 seconds. If not likely silicone fouled. If still OK, heat for two full minutes and watch for drops in voltage. Sometimes, the internal connections will open up under heat. This is the same a loose wire and is a failure. If the sensor is OK at this point, and will switch from high to low quickly as you move the flame, the sensor is good. Bear in mind that good or bad is relative, with port fuel injection needing faster information than carbureted systems.
ANY O2 sensor that will generate 0.9 volts or more when heated, show 0.1 volts or less within one second of flame removal, AND pass the two minute heat test is good regardless of age. When replacing a sensor, don't miss the opportunity to use the test above on the replacement. This will calibrate your evaluation skills and save you money in the future. There is almost always *no* benefit in replacing an oxygen sensor that will pass the test in the first line of this paragraph. " http://www.gnttype.org/techarea/ecms...O2sensors.html
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