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Discussion Starter · #1 ·
hello guys,
i have a 2015, 1.0 engine with 66 hp Hyundai i10 with 70,463 miles. (the G3LA engine)
the check engine bulb is on for 4 years (since i bought the car)

the car doesn't have any weird noises or bad fuel consumption so i decided not to face with the problem all those 4 years.

now, as i want to sell the car, i have to face with the problem so my first step was to change the Upper O2 Sensor (the brand i changed for is EPS, its Italian company and Hyundai refers it as OE item)
with the O2 sensor replacement i also changed sparkplugs to original champion ones + Fuel cleaner BG K44 + oils and filters Replacement.

the bulb went off for about 3 months, and now it returns back.

today, i went to a shop which perform "4 gas emission test" and the owner of the shop told me that the results are absolutely fine and to not buy a new catalytic converter.

now, i really dont know what to do from here. please your help
 

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2008 Accent 3 dr 5 sp manual; 2010 Genesis Coupe 2LT track 6 sp manual
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It's the post cat sensor that trips the P0420. If you can monitor the post cat O2 sensor voltage when warmed up and at a steady speed. It should be held steady above .550v or so, usually near .700v. the volts will drop when you let up on the throttle for any length of time.

If it is rapidly cycling ( like the pre cat O2 does) the cat is bad or if at steady .450v or lower, the sensor is bad.
 

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Discussion Starter · #3 ·
It's the post cat sensor that trips the P0420. If you can monitor the post cat O2 sensor voltage when warmed up and at a steady speed. It should be held steady above .550v or so, usually near .700v. the volts will drop when you let up on the throttle for any length of time.

If it is rapidly cycling ( like the pre cat O2 does) the cat is bad or if at steady .450v or lower, the sensor is bad.
how do i monitor the post cat sensor? what tools should i need to have?
I have got OBD2 scanner if its helping
 

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2008 Accent 3 dr 5 sp manual; 2010 Genesis Coupe 2LT track 6 sp manual
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The O2 sensor voltages are a standard OBDII protocol so any OBD data reader should be able to see them.
 

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2016 Elantra GT and 2011 Elantra Touring
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today, i went to a shop which perform "4 gas emission test" and the owner of the shop told me that the results are absolutely fine and to not buy a new catalytic converter.
Why not ask what they thought the problem was?
 

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Discussion Starter · #6 · (Edited)
It's the post cat sensor that trips the P0420. If you can monitor the post cat O2 sensor voltage when warmed up and at a steady speed. It should be held steady above .550v or so, usually near .700v. the volts will drop when you let up on the throttle for any length of time.

If it is rapidly cycling ( like the pre cat O2 does) the cat is bad or if at steady .450v or lower, the sensor is bad.
by saying "post cat O2 Sensor" you mean the O2 before the cat?
because if yes, i already replaced him by new one which was gave me 3 month without the P0420 code..
 

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2016 Elantra GT and 2011 Elantra Touring
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I had a car that would occasionally throw a P0420 code. The problem was a small leak in the exhaust near the second or post O2 sensor. This leak can even be slightly down stream of the sensor. If your car has a flex joint in the exhaust, it may have a small crack that opens up when the engine twists under load. A good inspection of the exhaust system may be in order.
 

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hello guys,
i have a 2015, 1.0 engine with 66 hp Hyundai i10 with 70,463 miles. (the G3LA engine)
the check engine bulb is on for 4 years (since i bought the car)

the car doesn't have any weird noises or bad fuel consumption so i decided not to face with the problem all those 4 years.

now, as i want to sell the car, i have to face with the problem so my first step was to change the Upper O2 Sensor (the brand i changed for is EPS, its Italian company and Hyundai refers it as OE item)
with the O2 sensor replacement i also changed sparkplugs to original champion ones + Fuel cleaner BG K44 + oils and filters Replacement.

the bulb went off for about 3 months, and now it returns back.

today, i went to a shop which perform "4 gas emission test" and the owner of the shop told me that the results are absolutely fine and to not buy a new catalytic converter.

now, i really dont know what to do from here. please your help
Make sure you have a clean air filter. If you don't, crap can be pushed past the air filter and into the engine and contaminate the CC and sensors.
 

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Discussion Starter · #12 ·
It's the post cat sensor that trips the P0420. If you can monitor the post cat O2 sensor voltage when warmed up and at a steady speed. It should be held steady above .550v or so, usually near .700v. the volts will drop when you let up on the throttle for any length of time.

If it is rapidly cycling ( like the pre cat O2 does) the cat is bad or if at steady .450v or lower, the sensor is bad.
hi, i purchased OBD2 Scanner.
i cant upload the full video but the front O2 sensor are rapidly moving between 0.03 to 0.8 Volts and the rear one are stuck exactly in 0.450 all the time.... does it mean that i have to replace the rear O2 sensor and the problem solved?

* i have to say that i did this test exactly as i turn up the car so i didnt gave a lot of time for the car to warm up. the temperature outside was around 30 celsius.
 

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Faulty diagnosis. Needs to be completely warmed up. Rear should not move much compared to front.
A scan tool is only as good as the person using it. You need to learn what these numbers mean.
 

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Discussion Starter · #14 ·
Faulty diagnosis. Needs to be completely warmed up. Rear should not move much compared to front.
A scan tool is only as good as the person using it. You need to learn what these numbers mean.
so maybe you can help and tell me what those numbers mean so i can do a proper test next time
 

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2008 Accent 3 dr 5 sp manual; 2010 Genesis Coupe 2LT track 6 sp manual
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0.455v and no change is a dead sensor. That is the default ECU value that is used normally until the post cat sensor warms up and starts working, usually in under a couple miles.

Be sure the O2 fuses are good!
 

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2016 Elantra GT and 2011 Elantra Touring
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scannerdanner.com forum is a good place to post the symptoms of your car and the numbers provided by the scanner. There's a good group of guys over there and I hate to see components replaced without being sure they are faulty.
 

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Discussion Starter · #19 ·
0.455v and no change is a dead sensor. That is the default ECU value that is used normally until the post cat sensor warms up and starts working, usually in under a couple miles.

Be sure the O2 fuses are good!
ok i have warmed up the car for 10 minutes of driving.
the values are:
O2S1-1 are going up and down between 0.070 to 0.675 with no throttle. (with throttle is 0.015 to 0.775)
OS21-2 are going up and down between 0.645 to 0.695 with no throttle (with throttle is 0.020 to 0.745)
 

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ok i have warmed up the car for 10 minutes of driving.
the values are:
O2S1-1 are going up and down between 0.070 to 0.675 with no throttle. (with throttle is 0.015 to 0.775)
OS21-2 are going up and down between 0.645 to 0.695 with no throttle (with throttle is 0.020 to 0.745)
That's pretty good. No problem with those numbers as long as the rear is not switching fast like the front.
 
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