2004 Suburban 1500 4WD with po420 code

Discussion in 'Domestics' started by dman, Sep 1, 2008.

  1. dman

    dman Newbie

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    Bought used 04 suburban with 75,000 miles now with 89k. Engine light came on earlier in the year, took it to my local mechanic who diagnosed code po420. Light came back on a few weeks ago, took it back to mechanic, thought it was the o2 senors but he rechecked code that was the same as before with message cat. below threshold. Was told that it would run between 8-12 hundred bucks to fix! Are there any other options? What would cause a cat. converter to go bad in a fairly new vehicle? I'm not very knowledgeable about cars but I've sure've done a lot of research since! truck runs well, no other issues and sure hope that it doesn't happen.

    Dman
     
  2. Tuscanskipper

    Tuscanskipper Newbie

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    Two things to think of that might make the cat fail.

    If the O2 sensors were bad before, they might have made the mix rich enough to plug the cat with carbon. Is there any other cause that might be making the mix rich on your vehicle?

    The other thing that causes this is blow by and excess oil consumption. What is the oil consumption of your vehicle? If it is excessive I think you have your answer.

    I had a cat fail, on a merc 320 4matic that I just sold, that fell apart internally, for no obvious reason. But that one suddenly started to rattle like crazy.

    If the problem with your cat is plugging, then there will be back pressure at the exhaust outlets. I have seen people let this get so bad, the engine won't develop revs or any decent power! If plugging of the cat is the problem, you will have to bite the bullet.
     
  3. crunch

    crunch wrench

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    Proper testing first.
    Code does not say replace the cat but to test it out.
    Leading cause of cat codes id rich running engine or engine missfire.

    http://www.troublecodes.net/articles/catfailure/

    Post back results of proper testing.

    DTC P0420, P0421, and P0430 & P0431: Check Possible Cause Of Misfire DTC P0420 and P0421 indicate bank one catalyst system efficiency is minimum requirement. DTC P0430 and P0430 indicate bank 2-catalyst system efficiency is minimum requirement. Possible causes are as follows: Use of leaded fuel. Oil contamination. Cylinder misfire. Fuel pressure too high. HO2S sensor improperly connected. Damaged exhaust system component. Faulty ECT sensor. Faulty HO2S. Ensure ignition timing is correct. Retrieve all Continuous Memory DTCs. If misfire code is not present, go to next step. If misfire code is present, isolate cylinder and repair as necessary. Check HO2S Monitor DTCs If DTCs P0136, P0138, P0140, P0141, P0156, P0158, P0160, or P0161 were present in step 1), service as necessary before continuing. If none of these codes are present in step 1), go to next step. Check ECT Sensor DTCs If DTCs P0117, P0118, P0125 or P1117 were present in step 1), service as necessary before continuing. If none of these codes are present in step 1), go to next step. If any codes except P0420, P0421, P0430 and/or P0430 were present in step 1), service as necessary before continuing. If no codes except P0420 and/or P0430 were present in step 1), go to next step. Check Rear HO2S Wiring Harness Turn ignition off. Ensure HO2S wiring harness is correctly routed and connectors are tight. Repair or replace as necessary. If wiring harness and connectors are okay, go to next step. Check Fuel Pressure Turn ignition off. Release fuel pressure. Install fuel pressure gauge. Start engine and allow to idle. Note fuel pressure gauge reading. Increase engine speed to 2500 RPM and maintain for one minute. For fuel pressure specifications, see FUEL PRESSURE SPECIFICATIONS article. If fuel pressure is as specified, go to next step. If fuel pressure is not as specified, go to CIRCUIT TEST HC. Check For Exhaust System Leaks If exhaust system leaks, it may cause catalyst monitor efficiency test to fail. Inspect exhaust system for cracks, loose connections or punctures. Repair or replace as necessary. If exhaust system is okay, go to next step. Check For Exhaust System Restrictions Inspect exhaust system for collapsed areas, dents or excessive bending. Repair or replace as necessary. If exhaust system is okay, go to next step. Check Manifold Vacuum Install tachometer. Connect vacuum gauge to intake manifold vacuum source. Start engine and raise engine speed to 2000 RPM. Manifold vacuum should rise to more than 16 in. Hg. If manifold vacuum is okay, go to next step. If manifold vacuum is low, go to step 11). Leave tachometer and vacuum gauge connected. Start engine and raise engine speed to 2000 RPM. On a non- restricted system, manifold vacuum should quickly rise to normal range as increased RPM is maintained. On a restricted system, manifold vacuum will slowly rise to normal range as increased RPM is maintained. If manifold vacuum is okay, no indication of exhaust leak or restriction has been detected and testing is complete. If manifold vacuum is low or slow to respond, go to next step. Leave tachometer and vacuum gauge connected. Remove exhaust pipe from exhaust manifold. Start engine and raise engine speed to 2000 RPM. If manifold vacuum is now okay, fault is downstream from exhaust manifold. Reconnect exhaust pipe to exhaust manifold and go to next step. If manifold vacuum is still low or slow to respond, fault is in exhaust manifold or intake manifold gasket. Repair or replace as necessary and repeat QUICK TEST. Leave tachometer and vacuum gauge connected. Disconnect muffler/tailpipe assembly from rear of catalytic converter. Start engine and raise engine speed to 2000 RPM. If manifold vacuum is now okay, fault is in muffler/tailpipe assembly. Repair or replace as necessary and test-drive vehicle to verify elimination of symptom. If manifold vacuum is still not okay, fault is in catalytic converter. Repair or replace as necessary. Check tailpipe/muffler assembly for debris from catalytic converter. Test drive vehicle to verify elimination of symptom.
     
  4. wap

    wap GO MOUNTAINEERS

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    p0420 - the most misleading code there is. It only indicates the the downstream o2 reading is very similar to the upstream reading. Could be many reasons. An exhaust leak before the cat, bad o2 sensor (s), egr valve issue, vac line issue, intake manifold issue etc. cat convertors are designed to last the life of the vehicle, and if the car has less than 80k miles, or less than 80k and less than 8yrs old, it is covered under warranty. This po420 is almost always caused by something else unless the cat has visible damage. A good exhaust shop would be my recommendation, and be careful here that you get a obdII compliant cat convertor if that is determined what is truly wrong. aftermarket obd compliant convertors are normally installed for about $250 each. a reflash of the computer may solve this problem as well. good luck....wap
     
  5. dman

    dman Newbie

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    Thanks for the help! I have a scheduled appt. with the Chevy dealer this wk end.
     
  6. crunch

    crunch wrench

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    When you get there.
    Tip on going to the dealer
    Ask that only a factory certified gasoline engine performance specialist work on your car.
    Not all dealerships are concerned with how repairs are dispatched, and not all dealership techs bother to take advantage of the training offered by factory (the vast majority of which is paid training).
    Some dealers will stick the grease monkey or wash bot on it and charge the full tech wage/rate for working on it.
    If the dealer is uncooperative, ask for your money back and call around for a dealer that will accommodate you.

    Good Luck and let us know how it goes.
    Crunch
     
  7. dman

    dman Newbie

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    Crunch,

    Followed advice, went to chevy dealer. They explained that left side of cat. converter (2. 0) needs to be replaced due to an internal converter in the cat. converter. Total cost of $960 which includes 2 gaskets (are gaskets a part of replacing the converter?) Told them I would get back with them.
    Thoughts?

    Darrel
     
  8. Gus

    Gus wrench

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    Your tech should have told you when the P0420 first happened, if the vehicle was under 80K at the time to be sent to a dealership for diagnosis.....if it was the cat, it would have been replaced for free....
     
  9. dman

    dman Newbie

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    I took my SUV to another an emission certified shop for a second opinion. The technician actually let me see how the process works! Anyway, the code says 0420 Cat. converter below efficiency Bank 1. So from what I've researched, Bank 1 could be a O2 Sensor and not necessarily the Cat, correct me if I'm wrong. He cleared the code and told me to drive if until it comes back on and bring it back in for a free diagnostics to see if its the same thing.

    Darrel
     
  10. Gus

    Gus wrench

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    Basically, you drive the vehicle and take a snapshot of the pre and post O2 sensors...if the post sensor is a mirror image of the pre sensor(and the sensor is changing normally), you need a cat....
     

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