2001 Chevy Impala Failed Emissions

  • 4 CYL
  • 2WD
  • 14,400 MILES
I recently had my 2001 chevy impala LS inspected to have it registered in DC. I failed and got several of the problems that they found fixed. This included new Coolant temp sensor/thermostat, sparkplugs/wires, air filter, PCV valve, E/GR valve and an oxygen sensor. However the check engine light is still on and the erroe code P0420 Catalyst System Efficiency Below Threshold (Bank 1) is still present. What does this mean that I need to repair and what do I absolutely need to purchase to fix this? I was told that a Catalic converter was needed, but is there another alternative that is less expensive?

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Monday, February 16th, 2009 AT 4:23 PM

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P0420 OBD-II Trouble Code
Technical DescriptionCatalyst 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.

SymptomsYou will likely not notice any drivability problems, although there may be symptoms.

CausesA 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 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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Monday, February 16th, 2009 AT 4:30 PM

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