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Check engine light comes on. failure 0420 i changed the

Customer Question
Check engine light comes...

Check engine light comes on. failure 0420 i changed the catalytic converter and the code 0420 stil apears

Mechanic's Assistant: Does the light stay on, or does it blink?

On

Mechanic's Assistant: What is the model/year of your Toyota?

2003 corolla

Mechanic's Assistant: Are you fixing your Corolla yourself? What have you tried so far?

I changed the catalytic converted not by my self

Submitted: 8 months ago.Category: Toyota
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Answered in 1 minute by:
12/23/2017
Toyota Mechanic: carguy1, auto technician replied 8 months ago
carguy1
carguy1, auto technician
Category: Toyota
Satisfied Customers: 27,794
Experience: 25 Years experience all makes and models.Nissan factory trained,Certified Subaru Tech
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Toyota Mechanic: carguy1, auto technician replied 8 months ago

There can be other causes for the code, a bad rear O2 sensor, poorly running engine, exhaust leaks can all lead to this code. You really need a scan tool that can read the sensor data to be sure the O2 sensors are working properly. Sometimes if you use an aftermarket converter it won't clean the exhaust enough and the code will return. I would also suggest filling at a different gas station. Sometimes the stations use additives that can cause the code as well.

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Customer reply replied 8 months ago
i have an obdII and can read errors and data from the ECM how can i tell that the O2 not good . what is the output values?
Toyota Mechanic: carguy1, auto technician replied 8 months ago

The rear O2 sensor should go from .3 volts to almost 1.0 volts, slowly like a nice rolling wave. If it doesn't get up to 1. or close and doesn't do it slowly that will mean the converter is not cleaning the exhaust. If it's going rapidly, that would indicate a bad sensor OR if it's sticking at one voltage. Make sure you aren't looking at the sensor heater when you are looking at this, but the input voltage from the sensor.

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Toyota Mechanic: carguy1, auto technician replied 7 months ago

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carguy1
carguy1
carguy1, auto technician
Category: Toyota
Satisfied Customers: 27,794
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Experience: 25 Years experience all makes and models.Nissan factory trained,Certified Subaru Tech

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