P0420 code repair?

Tiny
JOHNNY G
  • MEMBER
  • 2006 FORD EXPEDITION
  • V8
  • 2WD
  • AUTOMATIC
  • 85,208 MILES
How do I repair a code from my OBD-2 /code 420 Catalyst System Efficiency Below Threshold ( Bank 1). Spark plug, sensor, or is it my cat convt.
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Saturday, February 12th, 2011 AT 5:16 PM

3 Replies

Tiny
JACOBANDNICKOLAS
  • EXPERT
You could either have a bad O2 sensor on that bank, or the catalytic converter needs replaced. You need a live scanner that can read the voltage from the O2 sensor to confirm it is working correctly. From that reading, you can determine which to replace. NOTE: The O2 sensor can damage the converter if it is running too rich.
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Thursday, March 10th, 2011 AT 5:19 AM
Tiny
PKJFS
  • MEMBER
  • 1998 FORD EXPEDITION
  • V8
  • 4WD
  • AUTOMATIC
  • 200,000 MILES
I'm starting to get the p0420 trouble code in my expedition. I had it in a shop awhile back and the mechanic put in a "bypass" now the error code has come back. Does this mean that the catalytic is going bad or not?
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Thursday, November 12th, 2020 AT 7:42 AM (Merged)
Tiny
RASMATAZ
  • EXPERT
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 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
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Thursday, November 12th, 2020 AT 7:42 AM (Merged)

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