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How to test the O2 sensor on ford 250 5.4L 2008

I have p0420 code on my Ford 250 Super Duty.It says that the catalytic converter is bad. I want to make sure that it is correct testing the O2 sensors before replacing the cat

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Posted on Jan 02, 2017

CMV9
  • 594 Answers

SOURCE: Pulled code p0420 on 99 chevy astro, 2wd, v6

from what i am finding the code means o2 sensors. they recommend replacing them and if this does not work than replacing the cat converter

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.

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 soloutions

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. Many manufacturers give a five year, unlimited mileage warranty on these items. It's worth checking into.


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Posted on Aug 20, 2009

  • 318 Answers

SOURCE: P0420 and P0430

The AF sensors are uupstream and the O2 down stream. The car' s computer tests them and it is saying your cats are bad. If you have a scan tool you could look at the data and see what the sensors are seeing. The Af sensors are the ones that control the fuel ratio in the car while the O2's just watch. AF's would be the one to change but there is no garuatee that the codes won't come back.

Posted on Sep 25, 2009

SOURCE: converters

This started out as being a one code issue. I have no idea as to what you have done so far beyond what I have recommended. If you didn't take the intake off then there is no reason to believe the gasket is bad.

Posted on Jan 20, 2010

Rebgagnon
  • 382 Answers

SOURCE: 2000 Subaru Outback Wagon (100K miles) with P0420 Code

I do not know for sure if this is the problem you are having, But, I have noticed that from 95 up to 2002 I have seen a lot of PO420 codes that have been just the sensor. I do not know if it was a weak sensor or just that program telling it that it is below threshold. I did notice that if the vehicles are run for a long trip at highway speed it goes out. I wish you luck and have a great day.

Posted on Feb 11, 2010

  • 108 Answers

SOURCE: 2000 toyota celica fault code p0420 cat efficiency

Neither it probably is the catalytic converter. It is the sensor after the cat that is throwing codes.

Posted on Apr 09, 2010

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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.
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p0420 and p0430 both indicate a clogged catalytic converter. 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. The p0010 indicates camshaft sensor. The camshaft sensor may be the main problem, as it will affect your timing and fuel/air ratio, which in turn can effect what your Oxygen sensors detect, throwing the p0420 and p0430.

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