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CODE PO420 CONVERTER OR SENSOR? - Maxima Nissan Cars & Trucks

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This equates to Catalytic convertor bank 1, so I would get lambda sensor checked, more likely to be sensor or wiring rather than cat, going by the code

Posted on Oct 05, 2010

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Usually the converter, but you can check the sensor. interrogate the sensor connector with an ohmmeter and compare readings to another O2 sensor on the car.

Posted on Oct 05, 2010

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Posted on Jan 02, 2017

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SOURCE: PO420 code-service engine light is on

also check the cat by removing the o2 sensor befor the cat and look in the hole. if there is any deformity to the cat ( melted, holes, missing) replace it right away the nature of the 2.5l it sucks the cat matirial back into the motor damaging the rings and bearings. the most comon cause of cat failure on that modle is head gasket failure so before sinking 750$ in a cat have the head gasket checked.

Posted on Mar 29, 2010

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SOURCE: code po420 on scan tool but o2 sensor was replace 2 months ago

Hello and welcome. the code P0420 is for a bad cat. converter. replacing 02 sensors wont repair this code. the code simply's means that thje cat. converter is not working as designed and will need to be replaced.

The PCM determines the oxygen storage capability of the catalytic converter has degraded below a calibrated threshold.

Posted on Jul 03, 2010

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Trk won't pass inspection. It has the code PO420. catalys system below efficieny.


My father's 99 Suburban had a similar code for Bank 2(passenger side).Change the O2 sensors before and after the catalytic converter for the driver's side(cylinders 1-3-5-7).All four sensors are in the front section of the exhaust,just follow the pipe from the driver's side manifold to find the correct sensors.

Dec 08, 2012 | 1999 Chevrolet Silverado 1500

1 Answer

Po304 po307, i think my engine coils keep going out i also have a po420 code


You may have 1 bad coil not both #3 & & #7

You also have a bad exhaust converter from 10
years of on & off misfires

The PO420 is (Bank 1) Passenger side

Fix the misfires

Replace both Converters

Replace all 4 O2 Sensors

Converters should have lasted a few more years

A cop ignition coil is $59.00 & takes about 15 min to put in

No reason to pay someone $500.00

Jun 17, 2011 | 2000 Lincoln LS

1 Answer

My 2000 Cadillac Deville engine light on. Engine code PO420


Catalyst System Efficiency Below Threshold (Bank 1)

A code PO420 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 reading

  • 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

May 11, 2011 | 2000 Cadillac DeVille

2 Answers

Catalyst system efficiency below threshold


is that the code you get from comp is PO420 eng light if so worst news either you have an exh leak between o2 sensor 1 and o2 sensor 2 or the front o2 sensor is lazy or the front catyletic converter is not working

basicaly code is only triggerd when engine is hot and the front o2 sensor and the rear o2 sensor read the same voltage when conv is working the front o2 sensor will fluctuate rapidly from 0v to 1v and rear o2 sensor will remain steady at 0.5v

try to explain best i can plz vote comment or reply if you need more help

Jan 17, 2011 | Chevrolet Astro Cars & Trucks

1 Answer

Code po420 on scan tool but o2 sensor was replace 2 months ago


Hello and welcome. the code P0420 is for a bad cat. converter. replacing 02 sensors wont repair this code. the code simply's means that thje cat. converter is not working as designed and will need to be replaced.

The PCM determines the oxygen storage capability of the catalytic converter has degraded below a calibrated threshold.

Jul 03, 2010 | 2004 Mazda RX-8

3 Answers

Po420 code monte carlo ls 2001


PO420 code is for catalyst system efficiency below threshold (bank 1) Usually it means that it is time for a new catalytic converter on bank number 1. Cylinder bank number 1 is always the bank with the number 1 spark plug in it.

Apr 20, 2010 | 2001 Chevrolet Monte Carlo

2 Answers

Check engine light on PO420 code ? recalls


Huge problems with these cars. The Pre-cat converter is built into the exhaust manifold. Expensive to replace. No Recall on this item. Some say that inferior compounds in the catalyst cause corrosion and early wear of the piston rings. I have seen one of these use 5 qts of oil in 300 miles. Is this car using excess oil?

Jan 16, 2010 | 2005 Nissan Altima

1 Answer

PO420


Not just a faulty catalytic converter will trigger this code. Many other issues can trigger this code.

  • 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
  • Delayed spark timing
  • The oxygen sensors in front and behind the converter are reporting too similar of readings
Possible solutions:
  • Check for exhaust leaks at the manifold, pipes, catalytic converter.
  • Replace Coolant Temperature Sensor
  • 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 the catalytic converter
  • Have timing adjusted


Aug 25, 2009 | 2002 Toyota Camry

2 Answers

Fault code po420 ; is problem sensors or is it the cat conv


The only thing that will set this code is the catalytic converter or the oxygen sensor behind it. Way to tell if it is the sensor is to monitor voltage reading with scan tool and see if it is fluctuating the same as the upstream oxygen sensor. If it is the converter is "free flowing" and will have to be replaced. If the sensor is "flatlined" then it is most likely bad and setting the code.

Apr 30, 2009 | Ford Fusion Cars & Trucks

2 Answers

DTC P0420


first, code b0100 is a fault in the restraint system. front end sensor, restraint sensing diagnostic module or communication between the 2 are suspect problems po420 is an efficiency problem with catalytic converter. most likely would need new converter, but exhaust leaks and oxygen sensor malfuctions can also set code. if this vehicle is under 80,000 miles and does need converter, dealer should repair for free under warranty. that is federally mandated.

Dec 03, 2008 | 2005 Hummer H2

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