Question about 2003 Mitsubishi Lancer

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Service engine light is on code 0421

Autozone sais its code 0421 catalyst efficency low bank 1

ive noticed the light comes and goes usually after i fill the tank up it turns off wen the gas gets near a quarter of a tank give or take a little the light appears again . and i make sure the gas cap is tight ????

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  • lancerb113 Jan 13, 2009

    Thanks a bunch. I will try that ASAP!

  • poopycar Jan 27, 2009

    I have the same problem, did replacing the o2 sensor help, please let me know i got midas qouting me at $1200 to replace the catalytic converter

  • lancerb113 Jan 30, 2009

    thanks for your input on my problem. i havent had the time to replace the sensor its also a little pricey. $1200 sounds insane for a catalytic check out the link below its (ROADRACEMOTORSPORTS.COM) they sell a bolt on replacement cat for about $150 and and a weld on cat for $100 and watever a gasket would cost 2 or 3 bucks.dont kno how handy you are but the oem one one our car is a bolt on and with a little wd 40 it shouldnt be so bad to change. as soon as i can get to the sensor issue ill get back to . thanks again man appreciate it

    http://www.roadracemotorsports.com/store...

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Your number 1 O2 sensor is bad replace it. this is the O2 sensor attached to your headers. Could be faulty sensor or the air/fuel ratio is offset. But replace the sensor its not running effeciently.

Posted on Jan 12, 2009

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P0420 fault not going away


covers other aspects as well.

P0420 Chevrolet - Catalyst System Low Efficiency Bank 1 Repair Importance Level: 2/3 Repair Difficulty Level: 2/3 alt="What does this mean?"> alt="PDF"> alt="Share Code"> 3 alt="P0420 Chevrolet Comments"> ' Add Comment alt="Close Selection"> http://engine-codes.com/p0420_chevrolet.html Forum Code Possible causes - Three way catalyst converter Bank 1
- Exhaust tube
- Intake air leaks
- Fuel injectors may be faulty
- Fuel injector leaks
- Spark plugs may be faulty
- Improper ignition timing
- Powertrain Control Module (PCM)
alt="What does this mean?"> What does this mean? Tech notes As the code description implies the P0420 code means that the vehicle's control module has detected that the three-way catalytic converter is not working properly (is not as efficient as the factory is expecting). Replacing the oxygen (O2) sensors may sometimes fix the code, but in most cases the catalytic convert needs to be replaced to fix the problem. If the P0420 code is combined with other codes, try fixing the other codes first.
alt="What does this mean?"> What does this mean? When is the code detected? If a condition exists which causes the Powertrain Control Module (PCM) to detect excessive Bank 1 HO2S #2 activity outside of an acceptable range for an extended period of time, the PCM will set the P0420 code. This indicates that the three-way catalytic converters oxygen storage capacity is below a threshold considered acceptable. Possible symptoms - Engine Light ON (or Service Engine Soon Warning Light) P0420 Chevrolet Description In order to maintain a reasonably low emissions of Hydrocarbons (HC), Carbon Monoxide (CO), and Oxides of Nitrogen (NOx), the engine controls system uses a three-way catalytic converter. The catalyst within the converter promotes a chemical reaction which oxidizes the HC and CO present in the exhaust gas. This reaction converts them into harmless water vapor and Carbon Dioxide. The catalyst also reduces NOx, converting it to Nitrogen. The Powertrain Control Module (PCM) monitors this process using Bank 1 HO2S #2. Bank 1 HO2S #2, located in the exhaust stream past the three-way catalytic converter, produces an output signal which indicates the oxygen storage capacity of the catalyst. This determines the catalysts ability to convert exhaust emissions effectively. If the catalyst is functioning correctly, the Bank 1 HO2S #2 signal will be far less active than that produced by Bank 1 HO2S #1.


Read more: http://engine-codes.com/p0420_chevrolet.html#ixzz3n9JdbrFG

Sep 29, 2015 | 2009 Chevrolet Lumina SS

1 Answer

I have a 2002 yukon xl 1500 slt 5.3 and I took it to auto zone gave me a code of p0420.Do u have any suggestions on this code?And what can I do about it?I don't have any money and I need my vehicle.Can you...


P0420 GMC - Catalyst System Low Efficiency Bank 1 ' Add Comment
Possible causes
- Three way catalyst converter Bank 1
- Exhaust tube
- Intake air leaks
- Fuel injectors may be faulty
- Fuel injector leaks
- Spark plugs may be faulty
- Improper ignition timing
- Powertrain Control Module (PCM)
What does this mean?
Tech notes
As the code description implies the P0420 code means that the vehicle's control module has detected that the three-way catalytic converter is not working properly (is not as efficient as the factory is expecting). Replacing the oxygen (O2) sensors may sometimes fix the code, but in most cases the catalytic convert needs to be replaced to fix the problem. If the P0420 code is combined with other codes, try fixing the other codes first.
What does this mean?
When is the code detected?
If a condition exists which causes the Powertrain Control Module (PCM) to detect excessive Bank 1 HO2S #2 activity outside of an acceptable range for an extended period of time, the PCM will set the P0420 code. This indicates that the three-way catalytic converters oxygen storage capacity is below a threshold considered acceptable.
Possible symptoms
- Engine Light ON (or Service Engine Soon Warning Light)
P0420 GMC Description
In order to maintain a reasonably low emissions of Hydrocarbons (HC), Carbon Monoxide (CO), and Oxides of Nitrogen (NOx), the engine controls system uses a three-way catalytic converter. The catalyst within the converter promotes a chemical reaction which oxidizes the HC and CO present in the exhaust gas. This reaction converts them into harmless water vapor and Carbon Dioxide. The catalyst also reduces NOx, converting it to Nitrogen. The Powertrain Control Module (PCM) monitors this process using Bank 1 HO2S #2. Bank 1 HO2S #2, located in the exhaust stream past the three-way catalytic converter, produces an output signal which indicates the oxygen storage capacity of the catalyst. This determines the catalysts ability to convert exhaust emissions effectively. If the catalyst is functioning correctly, the Bank 1 HO2S #2 signal will be far less active than that produced by Bank 1 HO2S #1.

Mar 31, 2015 | 2002 GMC Yukon XL

1 Answer

2007 chevy impala p420 engine code


that is a low efficency bank 1 catalyst code, basically you need a new catalytic convertor

Jan 17, 2013 | Chevrolet Impala Cars & Trucks

1 Answer

What does a ******** Catalyst(TWC) system, low efficency service code mean? and where is it located


Exhaust Converter on Bank #1 side, is worn out,needs
to be replaced

PO420 &PO430 are Converters Below Efficiency

Should have lasted another year or two

I suspect you don't keep up on what the car
required,air filter,spark plugs,O2 Sensors & the like.

Your fuel trim & ignition issues over the years ruined it

Jun 02, 2012 | 2001 Cadillac Seville

1 Answer

Audi A4 Cabriolet Fault Code 0421


OBD2 Diagnostic Test Code (DTC) P0421 - Warm Up Catalyst Efficiency Below Threshold (Bank 1)


Basically this means that the oxygen sensor downstream of the catalytic converter on bank 1 is detecting that the catalyst is not working as efficiently as it should be. (Too much free oxygen in the exhaust downsream of the converter)

This can be caused by leaks in the exhaust system between the upstream O2 sensor and the downstream O2 sensor, but is usually caused by a converter that is chemically inactive or contaminated.

You didn't mention the year or mileage on your vehicle, but it should be noted that many manufacturers cover the catalyst under warranty for extended periods of time/mileage. If you live in the US, the manufacturer MUST warranty the catalyst for a MINIMUM of 8 years/80,000 miles per EPA mandates.

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2 Answers

Engine light stays on, code is p0420 low thresh bank 1.... where is bank 1 located


I'm not sure you understand the difinition of OBD2 fault code P0420, it means that Catalytic converter in the exhaust that is connected to the engine cylinder bank that contains number one engine cylinder has fallen below the a allowed threshold of cleaning pollunts from the engines exhaust stream. I would be more specific but you have not given model or year of the Mercury you have.
Here is the full difinition of OBD2 fault code P0420 from the factory service information system.


P0420 - Catalyst System Efficiency Below Threshold (Bank 1)


Possible causes - Three way catalyst converter worn out
- Intake air leaks
- Fuel injectors may be faulty
- Fuel injector leaks
- Spark plugs may be faulty
- Improper ignition timing
- Engine Control Module

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2 Answers

Check engine light on, code reads p0420


Hi and welcome to FixYa!

Code p0420 means Catalyst System Efficiency Below Threshold (Bank 1). This will surely needs attention to resolve the problem.

Hope this helps and thank you for using FixYa! Have a good one!

Jan 26, 2011 | 1999 Buick Century

1 Answer

PO420" Catalyst efficiency low Bank 1"


Replace the catalytic converter.

Mar 09, 2009 | 1999 Acura TL

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