Question about 2000 Mitsubishi Montero Sport

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Shooting code #p0420

Exhaust leak

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If you have an exhaust leak the hole allows the mixture that the secondary o2 reads to become high and will cause check engine light to come on. Fix the leak and reset the ecu by removing the negative bat terminal for ten seconds with one door open then reconn

Posted on Feb 14, 2014

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Posted on Jan 02, 2017

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Htd catalyst N/A catalyst efficiency below threshold bank1 01 chevy impala i have put a new cat, upstream& downstream o2 sensor in but im still getting p0420 code


When was the last time the spark plugs were changed?
Any oil or antifreeze useage?
NO exhaust or intake leaks?
NOT the slightest exhaust leak before the convertor?
Fix all above to clear the p0420.

Feb 07, 2018 | Cars & Trucks

2 Answers

What does trouble code p0420


p420 code has to do with your exhaust system,catylic converters,..sensors...could be a simple fix or not...

Sep 19, 2014 | 2003 Chrysler Town & Country

1 Answer

Trouble code p0420


The P0420 code means that the catalytic converter efficiency is below threshold. Since there are two oxygen sensors, above and after the catalytic converter, they together generate signals which are used to monitor the efficiency. However, if the catalytic converter is bad, the sensor after the converter will generate steady results, without any fluctuations.
You can replace the catalytic converter to overcome this problem. However, there are chances of the P0420 code to come up if there is any leak in the exhaust or the downstream o2 sensor (after the converter) is bad. Ideally, before spending on cat, you should try replacing the downstream sensor, which you can buy at low price from online stores like oxygensensorworld.com and also inspect for any small leaks in the exhaust system. Since the converter can cost you more, think of replacing it only if needed.

May 23, 2013 | Cars & Trucks

1 Answer

P0420 code evap system


This is not an evap code. Read on:
P0420 - Catalyst System Efficiency Below Threshold Bank 1

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
- Engine Control Module (ECM)
Tech notes The most common cause it the three way catalyst converter Bank 1. Changing just the O2 sensor usually don't repair the problem. If the P0420 code is combined with other codes, try fixing the other codes first.

Nov 02, 2012 | Cars & Trucks

1 Answer

I have 1999 gmc new Sierra Z71 1500 4wd 4.8 8cil shows code P0420 what can I do to fixed


P0420 - Catalyst System Efficiency Below Threshold (it not cleaning the exhaust up)
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
- Engine Control Module (ECM)

Oct 11, 2012 | Cars & Trucks

1 Answer

P0420 engine code


P0420 is a catalytic converter inefficiency code. The most likely problem is the catalytic converter is no longer able to function. The cat is monitored by the downstream O2 sensor. Unless there was a leak near that sensor than its unlikely (but not impossible) that an exhaust manifold leak is causing the problem.

What is possible is that the leaking exhaust manifold is skewing the readings for the upstream O2 sensors which could effect the life of the cat if the vehicle is running slightly richer than it should be.

Feb 24, 2012 | 2003 Hyundai Santa Fe

1 Answer

Getting P0420 code & P0303 code...why?


A code P0420 may mean that one or more of the following has happened:
  • Leaded fuel was used where unleaded was called for
  • An oxygen sensor is not reading (functioning) properly
  • The engine coolant temperature sensor is not working properly
  • Damaged or leaking exhaust manifold / catalytic converter / exhaust pipe
  • Retarded spark timing
  • The oxygen sensors in front and behind the converter are reporting too similar of readings
Possible SolutionsSome suggested steps for troubleshooting a P0420 error code include:
  • Check for exhaust leaks at the manifold, pipes, catalytic converter. Repair as required.
  • Use a scope to diagnose the oxygen sensor operation (Tip: The oxygen sensor in front of the catalytic converter normally has a fluctuating waveform. The waveform of the sensor behind the converter should be more steady).
  • Inspect the downstream heated oxygen sensor (HO2), replace if necessary
  • Replace the catalytic converter

Code p0303 means one cyliner is misfireing. Check spark plugs and wiring cables. If one cylinder isn't working good that could be the possible couse for the first code P0420 and all other engine problems.

Feb 25, 2011 | 2005 Isuzu Ascender

3 Answers

I had my car inspected and received P0420 code? what does it mean?


P0420 Error Code: Catalyst System Efficiency Below Threshold (Bank 1) Repair information for the OBD-II trouble code P0420 - Catalyst System Efficiency Below Threshold (Bank 1)
www.obd-codes.com/p0420

Feb 18, 2010 | 2000 Toyota Celica

2 Answers

P0401,P 0420, CODE IN HONDA ODYSEY


P0401- Bad EGR valve
P0420- Most likely cause is a bad O2 sensor(s) at the catalytic converter

Sep 08, 2009 | 2001 Honda Accord

1 Answer

CODE P0420


Check for any exhaust leaks, hopefully your not burning oil, or losing coolant, and have exhaust checked for possible plugged catalytic converter.

Apr 06, 2009 | 2003 Chrysler 300M

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