Plz~Need Help~

[kelvin314]

DEAR GUYS,

I have a 2001 Corolla T-SPRITE with ONLY 37,000 miles, and I've been driving around with a check engine light for quite some time.

The error was diagnosed as P0420, "Catalyst system efficiency below threshold - bank 1", and my mechanic replaced the O2 sensor and clean MAF for me,but the check engine light came back on after 50 miles, and I brought the car back to my mechanic,he thought problem come with CAT, before he replace that He did test on the emission, AND result which it is passed! 0_o!

the local garage suggested me to go to toyota dealer to check~then i took my car to there~and toyota car dealer said i need replace ECU AND CAT, cost me about 1800 pounds.i dont believe that..my car only 37000 miles, how does ecu and car both broke? but i dont know what else i can do?

so plz help~

Thanks guys~

[nrgizerbunny]

Here's the basics of how emissions on a car works.

On the intake two measurements are taken. Temperature of air and mass of air.

The ECU then calculates how much fuel it needs to spray into the inlet chambers to maintain stoichiometric combustion ratio (air to fuel of 14.7).

Once the exhaust gas pass out, it measures the amount of oxygen left in the exhaust gas.

The chances of a purely electronic component (ECU) failing is extremely small. Sensors fail all the time and I have been through 3 MAF sensor, the original and one that went faulty within a few months. Cleaning it is a waste of time. Buy a new one and I can pretty much guarantee your problem will go away.

[kelvin314]

Here's the basics of how emissions on a car works.

On the intake two measurements are taken. Temperature of air and mass of air.

The ECU then calculates how much fuel it needs to spray into the inlet chambers to maintain stoichiometric combustion ratio (air to fuel of 14.7).

Once the exhaust gas pass out, it measures the amount of oxygen left in the exhaust gas.

The chances of a purely electronic component (ECU) failing is extremely small. Sensors fail all the time and I have been through 3 MAF sensor, the original and one that went faulty within a few months. Cleaning it is a waste of time. Buy a new one and I can pretty much guarantee your problem will go away.

thank you very much for your replying~

from the internet i know thatlots of people changed o2 sensor and MAF sensor and CAT,then light still come back :eek:

anyway,i am going to ask my machenic to check MAF sensor for me..hope the problem come from MAF sensor.

the dealer said 1800 pounds its a huge money for me :crybaby:

thanks anyway guys

[jayt13]

You have very low miles for the age of the car.

[kelvin314]

plz anybody could help :crybaby:

[BRIDGES]

Have you changed your Cat for a sports cat or has less cells? This will more often that not bring the error up as it has done with me. Or do you have a funny smell in the car after a couple of miles of driving, this could be that your CAT is shocked IE needs replacing.

Have you reset your ecu via the fuses? If you did the error come back on straight or after/during driving?

I ask as i reset mine sometimes and the error pops up when im cruising at low speeds IE in a car jam!!

[kelvin314]

Have you changed your Cat for a sports cat or has less cells? This will more often that not bring the error up as it has done with me. Or do you have a funny smell in the car after a couple of miles of driving, this could be that your CAT is shocked IE needs replacing.

Have you reset your ecu via the fuses? If you did the error come back on straight or after/during driving?

I ask as i reset mine sometimes and the error pops up when im cruising at low speeds IE in a car jam!!

the first,thanks for replying..

i havent changed my cat to sport...and there is no smell from cat when dring..also, my machenic tested the emrission,it is passed 0_o~~

however,mechanic changed o2 sensor for me and cleaned MAF..i am afriad they did not reset ECU for me..

anyway, i am going to disconnect the Battery later..

hope its working..

thanks very much~~

[kelvin314]

update~~~

i did disconnect the Battery yesterday~

the CEL went off~

and i have been drive about 3 miles now :) still off now:)

god bless me la~hope off forever~

thanks everyone~

[kelvin314]

update again~~

drove about 23.4 miles~~~the CEL back on again :ffs: :ffs:

checked MAF sensor, its fine~checked CAT,its fine~

WTF IS IT :ffs:

HELP GUYS~PLZ~

[leepulsar]

p0420 you need a new cat

[kelvin314]

p0420 you need a new cat

but my cat is working very good

[BRIDGES]

Thats the error i get with my sports cat. You may not need a new cat, you can tell when you need a new cat as it stinks the whole vehicle out its a horrible smell.

What i got told is because theres two sensors they measure the flow of gases if its out a little then it will trigger the management light because its not set to what the ecu is set as.

I know you got your exhaust tested but mine past also with 200cell with the management light on, the difference in emmissions is minimal but its huge for the ECU. Maybe your pre-cat and downpipe is knackered. Try pricing one up, if not get a custom downpipe made with no pre-cat.

[leepulsar]

tell you need a new cat it aint working only tryin to help but what do i know ive only worked for toyota 10 years and a master tech lol and there around 650 new

[rota2010]

Hi there i had the same problem with my old corolla tsport, toyoya told me it was an o2 sensor on the cat, they replaced it, then had the same problem again and they suggested to change the other o2 sensor. 500 pound later and still had the problem. In the end i had the AA plug in their machine which is an older OBD2 machine from the toyota one which reads the error codes, it turned out to be the MAF Sensor which plugs into your air filter. hope this Helps