Question about 2002 Nissan Altima

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Check engine light is on. Code reads p0420? Is it a sensor or something else?

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HI. This is a sign of a catalytic converter that is not working as efficiently as it should be. It is part of the vehicle emissions system. The catalytic converter has an oxygen sensor in front and behind it. When the vehicle is warm and running in closed loop mode, the upstream O2 sensor waveform readings should fluctuate, but the downstream O2 sensor reading should be fairly steady. If the PCM detects that the two O2 sensors are reading in a similar manner, the DTC code P0420 will be issued. The necessary action are to check for any exhaust leaks at the manifold, pipes and catalytic converter. You will also need to check the spark timing to insure that it is normal and inspect the coolant temp sensor for its integrity. If all the check points test out ok, the remaining actions will be to replace your catalytic converter. A lot of the emission parts are covered under the warranty package if the vehicle is not out of its warranty contract. If you still have full warranty coverage at this time, this repair should be covered. I would check that out before purchasing any parts.

  • NOTE_ This code could also be triggered by using a leaded fuel in the vehicle. Make sure you are using the correct fuel blend. I should also point out that this is not a sensor issue. Your sensor(s) are actually functioning as designed. If they were not, you would not have this code. With that said; it wouldn't hurt to test them, if possible.

Posted on Aug 24, 2010

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Http://www.obd-codes.com/p0420 hope this helps you

Posted on Aug 24, 2010

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Posted on Jan 02, 2017

keithheavili
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SOURCE: want to change the O sensors

I would definitely go with the Bosch brand and there are only two oxygen sensors.  One before and one after the catalytic converter.  As far as how hard they are to change out I don't know on your particular vehicle.  Here in the states you can borrow a tool from your auto parts store to help you take it out but I don't know if that would be available to you.  I just did the sensors in my father's Isuzu Trooper with a 22 mm wrench.  If you can get access to them, they are easy to change.  Just unscrew and screw them back in.  

Posted on May 18, 2009

  • 295 Answers

SOURCE: 1999 Honda Odyssey p0420 Error Code

Cat efficentcy. replace the converter.

Posted on Jul 07, 2009

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SOURCE: vsc and check engine light is on

DTC P0420: Catalyst System Efficiency Below Threashold (Bank 1)

The ECM uses sensors mounted before and after the three-way catalyst (TWC) to monitor its efficiency. The first sensor, and Air Fuel ratio (A/F) sensor, sends pre-catalyst A/F ratio information to the ECM. The second sensor, a heated oxygen sensor (O2S), sends post-catalyst information to the ECM. The ECM compares these two signals to judge the efficiency of the catalyst and the catalyst's ability to store oxygen. During normal operation, the TWC stores and releases oxygen as needed. The capacity to store oxygen results in a low variation in the post-TWC exhaust stream as shown below.
If the catalyst is functioning normally, the waveform of the heated oxygen sensor slowly switches between RICH and LEAN. If the catalyst is deteriorated, the waveform will alternate frequently between RICH and LEAN. As the catalyst efficiency degrades, its ability to store oxygen is reduced and the catalyst output becomes more variable. When running the monitor, the ECM compares sensor 1 signals (A/F sensor) over a specific amount of time to determine catalyst efficiency. The ECM begins by calculating the signal length for both sensors (for the rear oxygen sensor, the ECM uses the output voltage signal length). If the oxygen sensor output voltage signal length is greater than the threshold (threshold is calculated based on the A/F sensor signal length), the ECM concludes that the catalyst is malfunctioning. The ECM will turn on the MIL and a DTC will be set.
Hope this helps :)

Posted on Oct 19, 2009

SOURCE: check engine light on, code reads p0420

P0420- Catalyst System Efficiency Below Threshold Bank 1

Possible Causes:
- Three way catalyst converter Bank 2
- Exhaust tube
- Intake air leaks
- Fuel injectors may be faulty
- Fuel injector leaks
- Spark plugs may be faulty
- Improper ignition timing
- Engine Control Module

Possible Solutions:
The most common cause is the three way catalyst converter Bank 1. Changing just the O2 sensor usually don't repair the problem.

A three way catalyst converter(Manifold) with high oxygen storage capacity will indicate a low switching frequency of heated oxygen sensor 2. As oxygen storage capacity decreases, the heated oxygen sensor 2 switching frequency will increase.

When the frequency ratio of heated oxygen sensors 1 and 2 approaches a specified limit value, the three way catalyst (Manifold) malfunction is diagnosed.

catalytic_converter.gif

Posted on Jan 26, 2011

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SOURCE: Check engine light comes on

p0420 is set when the convertor is unable to store oxygen in the minerals used in the convertor. the lack of oxygen to mix with the exhaust gases causes the O2 sensor to set the code. if the O2 sensor has been replaced the only other thing to do is replace the convertor. you can check with the Subaru dealer and let them run your VIN to see if you had one of the defective convertors.

Posted on Aug 01, 2011

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My 2005 chevy equinox keeps showing problem code P0420 How do I fix this problem?


0 2 sensor near the catalytic converter or

replace the catalytic converter

The downstream O2 sensor reading should be fairly steady. Typically the P0420 code triggers the Check Engine Light if the readings of the two sensors are similar.

Read more at: https://www.obd-codes.com/p0420
Copyright OBD-Codes.com

https://www.obd-codes.com/p0420

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What means catalyst Efficiency below normal


      Got it scanned and it's P0420: Catalyst efficiency below thresholdbank 1. They said it could be a bad catalytic converter or oxygen sensor. I borrowed a scanner and tried to measure the oxygen sensor readings over time.Sep 8, 2011

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Code p0420 acura m'dx


1996-newer (OBD-II) vehicles use oxygen sensors and a catalytic converter to reduce emissions. There is one O2 (oxygen) sensor in front of the catalytic converter (called upstream), and one behind it (downstream). When the engine is warmed up and running normally the upstream oxygen sensor reading fluctuates and the downstream one is fairly steady. In the case where both readings are fairly steady, a P0420 check engine light code is set.
Possible Causes: Oxygen (O2) sensor not working correctly
Damaged or leaking exhuast (pipe, manifold, catalytic converter)
Damaged catalytic converter
Diagnostic Help:
To diagnose a P0420 trouble code we begin by checking for exhaust leaks under the vehicle. Then use an oscilliscope to check the waveforms of both upstream and downstream O2 sensors. The front reading should vary, the rear should be steady. Replace as necessary. Check the rear Heated O2 Sensor. Check the catalytic converter, replace if necessary. If necessary, check for wiring and component concerns. See our article "Automotive Circuit Testing 101", if you need more assistance with this. Remember to refer to an model-specific repair manual for proper instruction.

Jan 20, 2014 | 2005 Acura MDX

1 Answer

Have a p0420 code on 2000 celica should i replace o2 sensors or cat


The catalytic convertermag-glass_10x10.gif has an oxygen sensor in front and behind it. When the vehicle is warm and running in closed loop mode, the upstream oxygen sensor waveform reading should fluctuate. The downstream O2 sensor reading should be fairly steady. Typically the P0420 code triggers the Check Engine Light if the readings of the two sensors are similar. This is indicative of (among other things) a converter that is not working as efficiently as it should be (according to specs). It is part of the vehicle emissions system.

Feb 17, 2011 | 2000 Toyota Celica

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Check engine light on. P0325, P0420 2000 Subaru


CODE PO420 CATALYST SYSTEM EFFICIENCY BELOW THRESHOLD BANK I * CODE PO325 KNOCK SENSOR NO.1 CIRCUIT MALFUNCTION BANK NO.1 OR SINGLE SENSOR

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2 Answers

Code p0420 appears what does it mean engine lite came on


P0420 Catalyst System Efficiency Below Threshold (Bank 1)

What does that mean? The catalytic converter has an oxygen sensor in front and behind it. When the vehicle is warm and running in closed loop mode, the upstream oxygen sensor waveform reading should fluctuate. The downstream O2 sensor reading should be fairly steady. Typically the P0420 code triggers the Check Engine Light if the readings of the two sensors are similar. This is indicative of (among other things) a converter that is not working as efficiently as it should be (according to specs). It is part of the vehicle emissions system.


Symptoms You will likely not notice any drivability problems, although there may be symptoms.
Causes 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 Solutions Need a catalytic converter? Visit our catalytic converter shopping area for the lowest price on your replacement converter!
Some 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
One thing to note is that many vehicle manufacturers offer a longer warranty on emissions-related parts. So if you have a newer car but it's out of it's bumper-to-bumper warranty, there still may be warranty on this type of problem. Many manufacturers give a five year, unlimited mileage warranty on these items. It's worth checking into.

Nov 03, 2009 | 2007 Chrysler Town & Country LX New Cars

1 Answer

Check engine light-on OBD code's P0420 & P0430


The codes are Catalyst System Efficiency Below Threshold (Bank 1)&(Bank 2).

The catalytic converter has an oxygen sensor in front and behind it. When the vehicle is warm and running in closed loop mode, the upstream oxygen sensor waveform reading should fluctuate. The downstream O2 sensor reading should be fairly steady. Typically the P0420 code triggers the Check Engine light if the readings of the two sensors are similar. This is indicative of (among other things) a converter that is not working as efficiently as it should be (according to specs). It is part of the vehicle emissions system.

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
Some suggested steps for troubleshooting a P0420 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
One thing to note is that many vehicle manufacturers offer a longer warranty on emissions-related parts. So if you have a newer car but it's out of it's bumper-to-bumper warranty, there still may be warranty on this type of problem.

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1999 Honda Odyssey p0420 Error Code


Cat efficentcy. replace the converter.

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Code P0420


P0420 Catalyst System Efficiency Below Threshold (Bank 1)

There is one 02 sensor in front of the catalytic converter (called upstream), and one behind it (downstream). When the engine is warmed up and running normally the upstream oxygen sensor reading fluctuates and the downstream one is fairly steady. In the case where both readings are fairly steady, a P0420 check engine light code is set.

Possible Causes:
Oxygen (O2) sensor not working correctly
Damaged or leaking exhuast (pipe, manifold, catalytic converter)
Damaged catalytic converter

Mar 24, 2009 | Chrysler Concorde Cars & Trucks

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