Toyota corolla 2001 with code P0420

any codes for the evap system? if it never hits ready staut and the drive cycle is completed then it still has a problem!

So the CEL came on again, is it P0420 again or others? With these high miles its possile your CAT is going out. With a scantool check what your HO2 bank 1 sensor 2 is reporting in respect to bank 1 sensor 1. If both signal are samilar then its your CAT. Any exhaust leaks?

Hi I just got it checked by the dealer, and the post O2 sensor bank 1 sensor 2, does not show any reading, The pre sensor is showing 0.06, What does this mean

Is "pre sensor" bank 1 sensor 1? O2 bank 1 sensor 1 should fluctuate voltage from 0.1 to 0.9 volts. It goes up, down, up, down every second or so. It shouldn't stay at any one voltage. You'd need to watch it for 1-3 minutes. It is better graphed out. O2 bank 1 sensor 2 should give a voltage reading ( I'm not sure if the voltage stays steady or goes up, down on Sensor 2 ). You should try to get this sensor working - get a reading.

Hi Pre O2 sensor is bank 1 sensor 1, which is before cat, it shouws 0.06 milli volts and the post sensor, the one after cat, does not show any. According to dealer this means CAT is bad Ashish

Hi, I have a 2002 Toyota Corolla, I was driving and the Check Engine Light (CEL) came on at 135K. First I replaced the O2 sensors, as I figured at this mileage they were on their way out and I noticed a drop in the gas mileage. Looking back I should have held off as the CEL went on and off, and I decided to change. Well it came back on again. I had the CAT replaced after bringing to Toyota to have it diagnosed and Toyota wanted $1,500; I had it done for a tenth of that at a muffler shop. The light subsequently came back on again. I had been noticing well before the CEL came on, a rough and erratic idle, accompanied by a lack of power. I decided to replace the spark plugs and PCV valve as it was due after 84K miles since last replacing and notably the plugs were in decent condition for the mileage. Well the car still ran with a miss, so I decided to change out the ignition coil on plugs and this took away the miss. I also changed the MAF sensor which greatly reduced the annoying pinging I was getting. Alas, the CEL was still on, so I brought it back to the muffler shop and had them replace the CAT and everything after the exhaust, including the resonator pipe and the muffler. The CEL was cleared and hasn't come back! Basically, I had noticed I would step on the gas and there would be no power. I believe there was blockage in the muffler, which created back pressure in the exhaust and caused the CAT to have higher temperatures than allowed. This most likely caused the CEL to come on and at 140K at the time I finally changed the muffler and the rest of the exhaust; it was probably overdue anyway. So now I have a car that runs like brand new. I am sharing my story to hopefully help someone else here; perhaps it could be a bad muffler causing all of the trouble.

it's common but so are low quality aftermarket converters!

if you are conserned that the cat is defect it is simple for a shop to chect the output of the AF sensors for bank 1 , thats s1b1 s2b1 fi the cat is defect the s2b1 will folow the patern of the s1b1. If the cat is ok the s2b1 will be a flat line around 0.5 v. Thats if the person that is checking it has a clue what he is doing. ( sounds like the cat to me) you may want to ask the dealer if there was a reprogramming to correct this problem if i remember correct. or was it a new ECU. good luck

THat is, of course, if you're dealing with an o2 sensor. If it's an air-fuel sensor(which some are) then that test ^ is ineffective at testing for a bad cat.

Being that he postted it fixed in April I doubt he's concerned that the conveter is defective!

Whoops forgot to look at the date.

Hi all, I bought from a car dealer three days ago a secondhand Corolla 1.6 Linea Sol (year 2003), with 71000 km-s on it . After 300 kms the CEL came on. I took the car to Toyota service, where they found out that the error code is P0420. They told me that the ECU and CAT should be replaced, for a price about $2000 + $200 labour. Reading the previous comments in this topic, I have the feeling that Toyota wants to play me false. The CEL was cleared out by them. What do you propose me to do next time if I'll get the same error? Do I really have to change the ECU or check up first the exhausting system and CAT? Chaabee. According to the Toyota's expertise, the sensors are ok. (P.S. Sorry for eventual mistakes, I'm Hungarian)

Your English is actually quite good. First, the Toyota dealer is full of crap. DO NOT REPLACE THE ECM. P0420 indicates a catalyst has failed. Before the condemning the catalyst be sure there are no exhaust leaks in front of the catalytic converter. An air leak in front of cat could cause a false P0420. IF there are no leaks, then it's likely a catalytic converter. There's nothing in your post to suggest that the Computer needs replaced. They're crazy!

Darkrooms, thank you for your quick answer!

I live in NC and failed the inspections due to the P0420 code. I knew it would because the check engine light was on. The shop said it was the catalytic converter (even though on the printout it said the cat and the o2 sensor passed ) and I had the cat replaced and I have driven it around for almost 200 miles with various highway/city driving. I have taken it for 5 times after have the cat replaced and the darn thing won't pass STILL! It keeps having only 1 sensor say not ready. The guys at the shop say they have seen it a few times where the car has to be driven for a long time before it actually gets fully reset (which I have questions about). Should I take it and get a full blown engine diagnostic test? My car has 112,300 miles on it....but I don't think that has anything to do with it...last oil change I was advised to get a new battery sooner than later.......HELP! I am so confused!

What kind of codes do you have right now? Did the oil change place actually test your battery and charging system? If you have an electrical problem, you need to get that taken care of before anything else. Not only could it leave you on the side of the road, but low voltage can make the ECM throw false codes. By the way, if a shop replaced your catalyst and the vehicle is still not passing emissions, I would take it back and tell them its still not fixed!!