2001 Corolla, P0420, need advice

[bigpawn]

I purchased a 2001 corolla for my daughter. 150K
When the car was purchased it had p0420 light on, it needed a new converter.
The converter was replaced (aftermarket). The car runs great, it doesnt burn oil.
After 5 months the P0420 light came on again. I took it to the dealership and they
said it needed a converter. Cost $50.
I took the car back to the exhaust place that and re reaplaced the converter. He inspected the converter and it was clean. We both inspected it together.
He replaced it anyway, wasn't happy about it, but it was under warranty.
A month later the engine light came on again. it was a po420 code.
I took it back to the dealership and ask them if the rear o2 sensor was bad. They said it
wasn't. They said if the sensor was bad, it would give a different code.
They me told since it was an aftermarket converter that it wasnt up to toyota specs.
I was thinking about replacing the 02 sesnor anyway, but didn't want to spend the money on a sensor that wasnt bad.
Just need some simple advice. The dealership didn't seem to help at all. They want to replace the cat converter and they didn't even have one in stock.
Sincerely
cj

[bonnie*]

Hi There...

Code P0420 means Catalyst System Efficiency Below Threshold. Troubleshoot target area order is as under:

1) TWC : Threeway Catalytic Covertor, as you said you have replaced and recently inspected -OK.

IF ANYBODY KNOWS HOW TO CHECK CATALYTIC CONVERTOR, PLEASE SUGGEST.

2) Sub-heated oxygen sensor is located after catalytic convertor on an exhaust pipe.
This sub-oxygen sensor is slower in response than main one and does not contribute to air-to-fuel ratio. However, ECU uses this feedback for proper functioning of catalytic converter to maintain NOx contents in exhaust gases. This sub-oxygen sensor should hold fairly steady around 500mV~700mV.

If you can locate the electrical connector under the passenger seat besides the driver seat, Disconnect the connector precisely, try to check open or short on sensor side connector as well as ECU side connector. If there is no open or short found, re-connect it.

Start the car, run it idle for 2 to 3 minutes until it warms up properly. Try to measure the voltage by pining pointed probes of multi-meter, as stated it should read fairly steady around 500mV~700mV. If so, Sub-Heated Oxygen Sensor is OK.

You may follow above procedure to check main oxygen sensor as well.

3)The main oxygen sensor located after exhaust manifold and before catalytic converter. You can open the hood and try to locate exhaust manifold, if you can locate main oxygen sensor mounted either directly on exhaust manifold or on a small tail pipe attached to exahust manifold before catalytic convertor. The ECU uses this feedback from main oxygen sensor to maintain proper air-to-fuel ratio. The main O2 sensor voltage should vary fairly rapidly fast between about 200mV and 800mV.

But, as your problem is repeatitive, there wont be only P0420 one code. Try to know other codes, if available. Because sometimes ECU throws out funny codes and real cause is somewhere else.

Also try to check Engine Cooling System, EGR :Exhaust Gas Recycle System and EVAP system, this is you can check by yourself coz it's very easy. Or seek the openion from professionals. But, simply do not keep throwing new parts for the parts which are OK.

TRY TO READ THE THREAD, JUST FOR INFORMATION
http://www.toyotanation.com/forum/t171748.html

[bigpawn]

Thank you for your response.
I will try to check the sensor tommorrow.

There has only been the one code PO420. No other codes have come up.

I will also try to check the sensor before the converter.


You say
But, as your problem is repeatitive, there wont be only P0420 one code. Try to know other codes, if available. Because sometimes ECU throws out funny codes and real cause is somewhere else.

I can always run a check, the local Advance Auto Store will do it for free, no questions asked.
They even gave me the printout to take to the exhaust place. They were real friendly.
There has been only the one code all this time. I hope that info helps.
Thanks for your time
cj

[bonnie*]

Please provide us your complete feed-back, If you figured out the cause / faulty component for P0420 and already fixed this problem.

Tks
Bonnie*

[Flashmn]

IF ANYBODY KNOWS HOW TO CHECK CATALYTIC CONVERTOR, PLEASE SUGGEST.

Theres no way to test it.