Question about 2002 Chevrolet Blazer

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My blazer 2002 engine ight stays on. have replaced o2 sensors. have inspected cat converter.scan ttool reports CODE DTC PO420 Engine 4.3 litre

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  • brianckelly Jun 01, 2010

    HOW DO I RUN AN EMISSIONS TEST

  • brianckelly Jun 04, 2010

    how do i size a replcement cat converter for my
    2002 chev blazer?
    will operating it with shot converter cause other problems eg gas mileage

  • brianckelly Jun 05, 2010

    will operating it with shot converter cause other problems eg gas mileage?

    how do i select size for replacing.it ? ( is an import to australia and oem not available)

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3 Answers

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  • Master
  • 678 Answers

The code p0420 as you probably know is a Cat efficiency code. You did the right thing replacing the o2 sensors first. The code sets when the rear o2 sensors switching rate gets within a certain range of the front o2 sensors switching rate. A lazy slow switching sensor could set a false p0420 code. However, since you know you have good o2 sensors installed the catalytic converter is going to need to be replaced to get rid of the code. I suggest only using OEM converters. Nearly every aftermarket converter i've installed came back 6 months later with the same code. When we use OEM converters the code is gone for good.
If you end up spending the money on a new converter make sure your engine is running well and you have no missfire codes as that's a large cause of cat failures.

Posted on Jun 04, 2010

  • Christopher Foulkes Jun 05, 2010

    If the converter substrate isn't broken (you would know if it was, there would be a loud rattle from it when accelerating) there will be absolutely no driveability issues. You won't notice anything is wrong except for the bright light illuminated on the dash. If OEM isn't available any competent exhaust shop should be able to weld in a new catalytic converter. Or you can get an aftermarket part from your local parts supplier or an internet supplier such as rockauto.com. They have direct fit converters from 250-400.

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Code P0420 is a code for Catalyst efficiency. The computer is seeing the post Catalytic converter o2 sensor having too much activity. The Cat. should be cleaning the exaust of Hc, co, and Nox. The post cat o2 will read the o2 content in the exhaust and if it moves up and down too much or to high and low, the computer interperates that as the cat not ridding the exhaust of it's pollutants. This indicates that the converter is unable to preform properly. The problem could be a bad cat, o2 sensor (Pre- and/or post cat)or o2 sensor wires, or an air fuel mixture problem that has caused the cat to fail. Many other engine operating system failures can cause the converter to not work properly.

Posted on Jun 01, 2010

  • brianckelly Jun 02, 2010

    HOW DO I PERFORM EMISSIONS TEST? WITH SCANTOOL?IF IT IS A BAD CAT CA N IT CAUSE OTHER PROBLEMS EG POOR FUEL CONSUMPTION

  • brianckelly Jun 04, 2010

    how do i size a replacement?

    will operating it cause other problems eg gas milege?

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  • Chevrolet Master
  • 19,396 Answers

Hi.

P0420 is not necessarily the O2 sensor. The most common reason for this code is the cat converter itself. The tail pipe sensor is only rarely causing this DTC.

Observing the cat at a glance is not enough to find the fault. You will need to perform an emission test on the exahust system. You will probably find that emission are high because the cat converter must be replaced.
Do an emission test and eventually replace cat converter or full exhaust system, depending on conditions.

Regards.

Ginko.

Posted on Jun 01, 2010

  • 4 more comments 
  • Ginko
    Ginko Jun 01, 2010

    Hi.

    You run an emission test at the garage. You put a sensor into the tail pipe. The test is cheap.

    Sorry about the negative feedback received. You have to replace the cat, not the O2 sensor.

    Goodbye.


  • brianckelly Jun 02, 2010

    HOW DO I SIZE A REPLACEMT AFTER MARKET CAT ?ON ENGINE SIZE OR THE BIGGEST TO FIT AVAILABLE SPACE

  • brianckelly Jun 04, 2010

    how do i size a replacement?

  • Ginko
    Ginko Jun 04, 2010

    Hi.

    What engine does your truck mount?


  • Ginko
    Ginko Jun 05, 2010

    To get the right part, simply contact Chevrolet australia and get part number or purchase part:Welcome to Chevrolet Australia

  • Ginko
    Ginko Jun 05, 2010

    If price from Chevrolet is expensive, to purchase the part you can contact sellers like partstrain that ship outside US:Chevy Blazer Catalytic Converter - Catalytic Converters .

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1 Answer

Engine light code po420?


Code 420 refers to the catalytic converter in the exhaust pipe.
The code means the engine computer things the cat is not working correctly based on the data coming from the O2 sensors.
The sensors and the cat would need to be inspected.

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How many o2 sensore are on the 99 bravado? I replaced the o2 sensor before the cat converter, now code says bank one( before cat.) needs replacing. are there 4?


the sensor before the cat is NOT an O2 sensor but a HO2S sensor ( two different sensors with different operations). If this is a V6 engine there are 4 sensors -- 2 --HO2S sensors before the cats --one for each bank cat and 2 O2 sensors after the cats.
The fault code would have spelt out the correct sensor for replacing

Jan 24, 2015 | 1999 Oldsmobile Bravada

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Trouble code po420 2007 solstice


P0420 - Catalyst System Efficiency Below Threshold Bank 1xicon.jpghttp://engine-codes.com/p0420.htmlForum CodePossible causes- Three way catalyst converter Bank 1
- Exhaust tube
- Intake air leaks
- Fuel injectors may be faulty
- Fuel injector leaks
- Spark plugs may be faulty
- Improper ignition timing
- Engine Control Module (ECM) Tech notes The most common cause it the three way catalyst converter Bank 1. Changing just the O2 sensor usually don't repair the problem. If the P0420 code is combined with other codes, try fixing the other codes first.

Jul 06, 2012 | 2007 Pontiac Solstice Convertible

1 Answer

2002 toyota rav 4 / code po420 whats wrong ?


You have a cat converter ie eficiency code. Most shops are willing to sell you a cat converter and make a quick buck. However you can save some major money if you can find out what is wrong. A cat converter doesn't just go bad by itself something causes it to fail. Most likely a bad oxygen sensor or a dirty mass air flow sensor. I would replace the oxygen sensor in front before I replace converter. Reset check engine light and see if light comes back on. If it stays off you just save about 600 dollars. Oxygen sensors cause cat converters to go bad. So fix the cause first, then if you have to replace converter.

Oct 28, 2010 | 2002 Toyota RAV4

1 Answer

Code po420 on scan tool but o2 sensor was replace 2 months ago


Hello and welcome. the code P0420 is for a bad cat. converter. replacing 02 sensors wont repair this code. the code simply's means that thje cat. converter is not working as designed and will need to be replaced.

The PCM determines the oxygen storage capability of the catalytic converter has degraded below a calibrated threshold.

Jul 03, 2010 | 2004 Mazda RX-8

1 Answer

PO420 CATALYS INEFFICIENCY BELOW THRESEHOLD BANK 1.REPLACED CAT, 02,?


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.

Apr 18, 2010 | 2001 Chevrolet Monte Carlo

2 Answers

PO420 code-service engine light is on


P0420 Catalyst System Efficiency Below Threshold (Bank 1) first thing to do is go back to basics do a tune up (plugs) check the plug wires spray them with water or windex if you get a miss change them, run some fuel injector cleaner through it, don't just throw parts on it ,that is'nt cheap

Mar 24, 2010 | 2002 Nissan Altima

2 Answers

Code PO420 catalyst system efficiency below threshold


you may have a bad converter, its not cleaning the exhaust, but on the other hand a bad rear o2 sensor can also cause this problem,there is a wat to test but you would need a scan tool or scope,replace the other sensor, if light returns then replace the converter, no money lost, if you were to replace the converter the o2 sensors should also be replaced. you have 165000 miles it would be crazy not to replace sensor and install new cat, so basically your just doing it in 2 steps and may get lucky and not need a cat. good luck.

Mar 05, 2010 | 2001 Nissan Altima

1 Answer

2002 blazer zr2 check engine light code is po155 bank 2 sensor 2 where is it and how do I check it


P0155 is o2 sensor heater circuit malfunction bank 2 sensor 1 it is the o2 sensor circuit in front of the cat converter the o2 sensors are located mounted to the exhaust pipe in front and behind the catylic converter the problem is in the circuit [wiring or sensor itself] check wiring and repair if necessary if the short or open circuit is the sensor need to replace sensor +++ P0161 is 02 sensor heater circuit malfunction BANK 2 SENSOR 2 ++++++ this is the sensor behind the cat converter

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2 Answers

Keep getting code po420



Before Checking a Catalytic
Converter DTC
Before you troubleshoot an OBD II vehicle that stores
DTC P0420 (67) (catalyst system efficiency below
threshold), run these quick checks:
1. Check for a leak in the exhaust system. If you find
one, repair it, clear the DTC, and test-drive the
vehicle.
• If the DTC returns, go to step 2.
2. Connect the PGM Tester, and test-drive the vehicle
while an assistant monitors the voltage signal from
the secondary oxygen sensor (HO2S S2). After the
catalyst reaches operating temperature, the HO2S S2
voltage should stay between 0.5 and 0.8 V at steady
cruising speed. During deceleration, the voltage
should be steady at 0.1 V or less.
• If the voltage readings are OK, clear the DTC.
• At cruising speed, if the voltage fluctuates or stays
below 5 V, go to step 3.
3. Measure the inlet and outlet external temperatures of
the catalytic converter with a thermometer capable
of reading up to 500°F.
• If the outlet temperature is more than 100°F hotter
than the inlet temperature, the converter is OK.
• If the outlet temperature is less than 100°F hotter
than the inlet temperature, replace the converter.

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