Code P0421?

CHOOME

MEMBER
2006 MITSUBISHI ECLIPSE
3.8L
V6
2WD
AUTOMATIC
110,000 MILES

Thank you so much for replying to my question, your site is great. Anyhow, I was told that probably it wasn't my O2 sensor but a faulty catalytic converter or an exhaust leak. Is there any method to tell if it's an exhaust leak? I just don't understand why the same Bank2 Sensor 2 does not show any life in the live graph. It's flat. Thank you again.

7 Replies

JACOBANDNICKOLAS

MECHANIC
108,262 POSTS

Hi,

I'm not sure if you started a new thread, so bear with me. I'm not 100% sure what is happening.

As far as the code is concerned, it is specific to the warm-up catalyst (bank 1) is not working properly. I attached information below related to this code. It explains the code, what could be possible issues, and what to check.

Is this the only code you have? Also, the sensor you mentioned shouldn't stay flat at all times. Have you checked to see if there is a wiring or connection issue?

Take a look through this link, it explains how to test the sensor:

https://www.2carpros.com/articles/how-to-test-an-oxygen-sensor-02-sensor

Also, read through the attachments below and let me know if you are comfortable performing the tests.

As far as checking for an exhaust leak, the leak will need to be before the catalytic converters to affect the sensors. If it is at the exhaust manifold, often times it will sound like a ticking noise.

Here is a link that explains how to check:

https://www.2carpros.com/articles/step-by-step-guide-how-to-check-for-an-automotive-exhaust-leak

Take care,

Joe

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Friday, September 15th, 2023 AT 8:31 PM

CHOOME

MEMBER
7 POSTS

Thank you very much for your response. I Check the connection by putting a probe at the harness and got a 12volt reading, if that's right? All 3 Sensors read good except Bank2 Sensor2
Yes, I only have one code P0421 and I do hear a clicking noise which I've had forever but everyone says that it's the lifters
Below is info I got with Torque app from my wireless OBD11. Mayb it will bring some knowledge as I have no clue. Again thank you much for your time n info.

Freeze frame report generated by Torque for Android

Freeze frame information:

Fuel Status = 0 byte
Engine Load = 44.706 %
Engine Coolant Temperature = 89 °C
Fuel Trim Bank 1 Short Term = -0.781 %
Fuel Trim Bank 1 Long Term = 4.688 %
Fuel Trim Bank 2 Short Term = -1.562 %
Fuel Trim Bank 2 Long Term = 6.25 %
Intake Manifold Pressure = 8.557 psi
Engine RPM = 2,191.25 rpm
Speed (OBD) = 119 km/h
Timing Advance = 31 °
Intake Air Temperature = 32 °C
Mass Air Flow Rate = 28.48 g/s
Throttle Position(Manifold) = 22.353 %
Run time since engine start = 730 s
EGR Commanded = 60.784 %
Fuel Level (From Engine ECU) = 10.98 %
Barometric pressure (from vehicle) = 14.359 psi
Voltage (Control Module) = 14.208 V
Engine Load(Absolute) = 34.118 %
Commanded Equivalence Ratio(lambda) = 1
Relative Throttle Position = 16.471 %
Ambient air temp = 32 °C
Absolute Throttle Position B = 62.353 %
Accelerator PedalPosition D = 34.118 %
Accelerator PedalPosition E = 27.843 %

End of report.

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Saturday, September 16th, 2023 AT 8:41 PM

JACOBANDNICKOLAS

MECHANIC
108,262 POSTS

Hi,

The lifters wouldn't prevent the oxygen sensor from functioning. As far as the bank 2 sensor, there isn't a code, but that doesn't mean there isn't an issue.

If possible, record the noise you hear and upload it for me to hear.

When you check the voltage at an oxygen sensor (engine running), it should be between 0.1v and 1.0v. Where are you getting 12v?

Take a look at this link, it explains how to test one:

https://www.2carpros.com/articles/how-to-test-an-oxygen-sensor-02-sensor

Let me know.

Joe

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Sunday, September 17th, 2023 AT 1:06 PM

CHOOME

MEMBER
7 POSTS

Code PO421 - 2006 Eclipse V6 3.8l.
I guess it was miscommunication. You said the exhaust leak could make a clicking sound and I replied yes. I do have a sound but I've been told it was the lifters, All the 3 sensors seem good except B1 S2. In the live graph Its flat even after replacing 2x.
Could an exhaust leak or a bad C Converter affect the sensor? Cause all of it or 1 could give a Code PO421. Thank you for your response. But let me check before you reply. I don't want to burn you all out. Thank you so much for your help.

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Monday, September 18th, 2023 AT 12:50 AM

JACOBANDNICKOLAS

MECHANIC
108,262 POSTS

Hi,

The sensor shouldn't flatline. There should be a voltage reading even if the converter isn't properly working. It should also change when you hit the throttle.

Let me know.

Joe