Question about 1999 Chevrolet Astro

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

Pulled code p0420 on 99 chevy astro, 2wd, 160,500 miles. Says low-bank 1. Is this my cat converter or do you think its the o2 sensors??

Need to have emissions tested and it just failed. How would i fix the problem, or find out if its really the cat or the o2?

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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

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  • Chevrolet Master
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While it is hook up to the scanner, scroll to the o2 output readings

compare bank one senor one to bank one sensor two reading to each other. If they are inversely porportional they are working If one stays pretty mush where it is at, it is bad. Same goes for bank two. One way for you to locate the bad sensor is to go to the one you think it is and unhook it and read the scanner. If you have o volts you unhooked the right one. This is how the armatures can know which of the four sensors is the right one.

There is usually a Cat inefficacy code if the cat is bad. but not always.

hope this helps.

Posted on Aug 20, 2009

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Did they stick the probe up the tailpipe or just plug into the computer? With that many miles, it could be a catalytic converter, but if the o2 sensors have never been changed it could be them. If it is a sensor its probably the one behind the converter.

Posted on Aug 20, 2009

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