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I have an 06 saturn vue and it failed the emissions test. It says MIL Commanded. Is that hard to fix and a B1 Catalyst system efficiency below threshhold. Please help it needs to be inspected.

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  • Malissa Dickerson May 05, 2017

    Is the engine light on? low eff. is O2 sensor after cat. converter. Need codes to help



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B1 Catalyst system efficiency below threshhold , you need a new catalytic coverter . best to take to a qualified repair shop.

Posted on May 05, 2017


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I get OBD codes P0420 and P0430

P0420 and P0430

P0420 means Catalyst System Efficiency Below Threshold, Bank 1

P0430 means Catalyst System Efficiency Below Threshold, Bank 2

It means that the O2 sensors are good, and the O2 sensors are telling you that your catalytic converter, in the exhaust system is not working fine, as its emissions are polluting the air too much.

The catalytic converter is part of the exhaust system. The way to test this part is by doing an emission test. The two OBD codes that you are getting are already a test telling you that the converter must be replaced, unless an emission test done at a garage says the opposite.

This kind of problem will trigger the check engine light, and your car will also waste too much fuel.
You also risk to get in trouble if the car goes through an Air Pollution control, as the car won't pass an emission test in this condition.

To conclude, the Catalyst System must be replaced, the O2 Sensors are fine.

This is a repair that should be done at a garage, however you can find DIY instructions here:How to Replace a Catalytic Converter or you can get more detailed instructions, and step by step illustrated procedure purchasing a repair manual.

on May 27, 2009 | 2003 Chrysler 300M

1 Answer

Failed emissions test

First step is to have the code or codes read.If the "check engine light" is on there will be a reason and should be a code or codes to be read.Once you have the codes,you can determine the correction needed to get that "check engine light" out and a valid emissions test completed.Get back to us with the codes found.

Apr 28, 2017 | Saturn Vue Cars & Trucks

2 Answers

Catalyst system efficiency below threshhold bank 1

If your car is dumping excessive fuel it would set this light but more than likely, your Oxygen Sensor UPSTREAM is starting to fail...

Have you noticed a drop in your fuel efficiency?

Apr 16, 2013 | 2004 Toyota ECHO

1 Answer

2001 Ford Ranger 4 cylinder failed Emissions Test because MIL Commanded-ON failed. What do I do to repair or pass test?

so the mil is commanded on and yet you have no DTCs give an detailed account of the report for best results

Dec 07, 2012 | Dodge Stratus Cars & Trucks

1 Answer

I have a 2002 saturn vue that keeps going reduced power and it wont go over 30 mph why

It most likely is in a fail safe mode to protect it
from any damage

Usually that is exhaust converter damage, which is
govt emissions mandated

You should have a OBD2 MIL Lamp or some dash light lite

You address that problem, as you have all others & all
vehicles, for the last 30 years, since those systems have
been on all vehicles

You check for codes,then using factory trouble charts,
go to the system that the codes point to & then component

A cylinder misfire so severe it could damage the converter
is a common item & sometimes you get transmission
failsafes or overheating failsafes

Nov 20, 2012 | 2002 Saturn VUE

1 Answer

My check engine light came on with P0422 and P0455 codes. Any suggestions as to the cause.

P0422 - Catalyst below threshold.

Catalytic converter is clogged or out of medium.

Replace it.


Fault Code Definition
Code P0422 indicates that the Bank 1 Main Catalytic Converter's emissions efficiency has fallen below the minimum allowable limit. This threshold is tracked by a Catalyst Monitoring Oxygen Sensor located on or near the outlet of the Catalytic Converter.


* Check Engine Light will illuminate
* In many cases, no abnormal symptoms may be noticed

Common Problems That Trigger the P0422 Code

* Defective Catalytic Converter
* Engine misfires have damaged the Catalytic Converter
* Internal engine damage resulting in high oil consumption and/or a leaking Head gasket has damaged the Catalytic Converter

Common Misdiagnoses

* Oxygen Sensors are replaced when the real problem is a damaged Catalyst
* Catalyst is replaced when the real problem is internal engine damage, which is producing elevated emissions levels
* Catalyst is replaced when a misfiring engine is the real problem

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Aug 04, 2010 | 2008 Saturn VUE

3 Answers

Code p0420

Repair information for the OBD-II trouble code P0420 - Catalyst System Efficiency Below Threshold (Bank 1) Probably needs a catalytic converter

Apr 06, 2010 | 1999 Ford Contour

1 Answer

Check eng light with code po431 replased ox/sensors

P0431 is Warm Up Catalyst Efficiency Below Threshold (Bank 2). What is happening is this....the O2 sensor downstream of the Catalytic Converter is detecting the Converter is not working as efficiently as it should be (according to your cars specifications). 3 main causes of this is 1.) Defective O2 Sensor (which in your case elminates this one) 2.) Catalytic Converter is no longer functioning properly. or 3.) There is an exhaust leak. You will not notice any driveablitiy problems, however, you may get a rough/hard idle when its cold out. I would take your car to an exhaust shop and have them do a free exhaust system inspection. Alot of places like Midas/Mieneke Car Center/Monroe Muffler to name a few do these checks for free. Thanks for Using FixYa!



Dec 06, 2008 | 2003 Saturn VUE

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