Question about 1999 Chevrolet Silverado 1500

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Trk won't pass inspection. It has the code PO420. catalys system below efficieny.

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My father's 99 Suburban had a similar code for Bank 2(passenger side).Change the O2 sensors before and after the catalytic converter for the driver's side(cylinders 1-3-5-7).All four sensors are in the front section of the exhaust,just follow the pipe from the driver's side manifold to find the correct sensors.

Posted on Dec 09, 2012

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Posted on Jan 02, 2017

Molson02536
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SOURCE: PO420 CATALYS INEFFICIENCY BELOW

The PCM copares switch rates between the front O2 sensors and the downstream catalyst moniters. The catylist moniters are often mistaken as O2 sensors, and they are, but that is not their job, or what they are called.
By comparing the switch rates between the front (before cat) and rear (downstream of cat) the PCM knows if the cat is affecting the exaust, and how much it is affecting the exaust.
If it sees little or no effect o the exaust gases that have passed through the cat, then it decides that the cat is not working anymore, and sets a P0420, or a P0430, depending on which bank it is.
To check this yourself, you will need to bring up data stream on your scanner, watch the upstream and downstream O2 parameters and see if they are following each other closely.
If the cat is working right, you should see a fairly rapid switch rate, probably 5 or 6 times a minute on the front O2, but almost a flat line just above .5 volts on the rear. If the rear is switching often you proabably need a catalytic converter.
You can try resetting the ECM by turning your ignition to the on position (engine not running) and pulling the fuse to your ECM for 30 seconds and then placing it back in. Once the fuse has been reinstalled, start the car and let it idle for 1 min and then go for a test drive.
The engine may stall when you restart it, let is stumble and stall. Just restart it, the ECM is relearning the sensors like it was the first start up the engine ever had then go for a test drive.
This should reset everything and turn your check engine light off, if the check engine light came back on, have it scanned again at Auto Zone, Parts source where they scan free of charge and address the issues the DTC codes points out.
The easiest thing to do first is a visual check of things. Visually inspect the exhaust system for leaks, check the catalytic converter for dents, holes, severe discoloration, and check for a rattle inside. If any of those syptoms are there, the converter likely needs replacement.
Then, visually inspect the downstream O2 sensor (behind the converter). Check for broken wires, obvious faults, etc. If all that checks out, you'll want to check the operation of the O2 sensor. To do that, you'll need access to a scan tool or oscilliscope. Check that the waveform is pretty steady. If the reading fluctuates then the sensor is likely bad and will need to be replaced as mentioned earlier.
Thank you for using Fixya and be safe.

Posted on Apr 18, 2010

Molson02536
  • 3854 Answers

SOURCE: I have a 2001 MONTECARLO SS it has a Po420

There are a number of things that could be causing this p0420 catalyst efficiency code. The most common thing is the catalytic converter itself is no longer functioning properly. The other likely thing is the rear O2 (oxygen) sensor is no longer working properly. Other things could include exhaust leaks, damaged exhaust pipes, damaged O2 sensor wiring/connectors, plugged catalytic converter, etc.

The easiest thing to do first is a visual check of things. Visually inspect the exhaust system for leaks, check the catalytic converter for dents, holes, severe discoloration, and check for a rattle inside. If any of those symptoms are there, the converter likely needs replacement. Then, visually inspect the downstream O2 sensor (behind the converter). Check for broken wires, obvious faults, etc. If all that checks out, you'll want to check the operation of the O2 sensor. To do that, you'll need access to a scan tool or oscilloscope. Check that the waveform is pretty steady. If the reading fluctuates then the sensor is likely bad and will need to be replaced.

Chances are the O2 sensor has gone bad and needs to be replaced, you can pick one up at Auto Zone and they will have the step by step instructions to getting the job done. It's like replaceing a spark plug, you just have to get under the car to do it. Good luck and hope this helps.

Posted on Oct 30, 2009

  • 1608 Answers

SOURCE: im trying to get my

For the lean condition I wound look for vacuum leaks.I you don`t find any then replace the o2 sensor for bank 1.As for the po420 if the exhaust system is not bent or damaged you will have to replace the catalytic converter.The catalytic converter has a longer warranty then the regular vehicle warranty itself so call the dealership and find out if the converter is still under warranty.The usual warranty I believe is around 80k.mileage years is 7 or 8 not positive.Hope this helps.Good luck.

Posted on Sep 15, 2010

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For the lean condition I wound look for vacuum leaks.I you don`t find any then replace the o2 sensor for bank 1.As for the po420 if the exhaust system is not bent or damaged you will have to replace the catalytic converter.The catalytic converter has a longer warranty then the regular vehicle warranty itself so call the dealership and find out if the converter is still under warranty.The usual warranty I believe is around 80k.mileage years is 7 or 8 not positive.Hope this helps.Good luck.

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The actual error is

"Catalyst system below Threshold (bank 1)"

As mentioned above, the code's description is Catalyst System Efficiency Below Threshold (Bank 1). OK, now tell me that again in plain English please.... let's break it down: the catalyst system being referred to is your three-way catalytic converter; so the catalytic converter is not working properly (i.e. it's not efficient). Bank 1 refers to the side of the engine which contains cylinder #1. On inline engines such as 4 & 5 cylinder engines, there is only one bank. So, to really simply things let's just say that the efficiency of the catalytic converter and/or exhaust pipe and/or O2 sensor is not so great.

There are a number of things that could be causing this p0420 catalyst efficiency code. The most common thing is the catalytic converter itself is no longer functioning properly. The other likely thing is the rear O2 (oxygen) sensor is no longer working properly. Other things could include exhaust leaks, damaged exhaust pipes, damaged O2 sensor wiring/connectors, plugged catalytic converter, etc.

You can search for the Information on the web. Just type in the actual error above into you fav search engine!

Hope that helps...

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