1999 Suburban 5.7 - P0430 Code - Runs rough under load

Discussion in 'Chevy Suburban Forum (GMC Yukon XL)' started by number3480, Dec 18, 2013.

  1. number3480

    number3480 New Member

    First post for me. Would appreciate any help from you all.

    Our 1999 Suburban with the 5.7 began popping the check engine light on and off last spring. Over the summer, on a trip, it began running rough under load (up a hill or around 50-55mph).

    It has gotten worse and only occurs after the truck is heated up on the road. Doesn't do it cold or when idling.

    Had code read from O'Reilly's and it is P0430. I am hoping it is not a cat. Could it simply be a O2 sensor? Would that make it run rough?

    Any thoughts on where I should start would be great.


    99'HEARTBEAT MODERATOR Staff Member 5+ Years ROTM Winner 1000 Posts Platinum Contributor

    Welcome to the Site.....here's a little more Information regarding Trouble Code P0430, that may be able to help,

    Catalyst System Efficiency Below Threshold (Bank 2)

    What does that mean? Basically this means that the Oxygen Sensor Downstream of the Catalytic Converter on Bank 2 is detecting that the converter is not working as efficiently as it should be (according to specs). And Bank 2 is the Passenger-Side of the Vehicle.

    Symptoms You will likely not notice any drivability problems, although there may be symptoms such as a rough/hard idle when cold.

    Causes Code P0430 may mean that one or more of the following has happened:
    * The Catalytic Converter is no longer functioning properly
    * An Oxygen Sensor is not reading (functioning) properly
    * There is an Exhaust Leak

    Possible Solutions First, Inspect for Exhaust Leaks. Next step is to Measure the Voltage at the Oxygen Sensor on Bank 2. In fact, it would be a good idea to Test Each Oxygen O2 Sensor while you're at it.
  3. number3480

    number3480 New Member

    Thanks for the reply. Stopped by Autozone to double check the light and also have P0161 & P0440 codes as well. Told that Po161 is likely related to P0430 code. Going to test the sensors and hope the cat isn't bad.
  4. FireRed

    FireRed Rockstar 100 Posts

    There are quite a few ways to clean the cat, do a Google search, I know of a few that used acetone also carb cleaner shot into a small hole just before the cat. The hole gets plugged with a screw when done.
  5. USAF-Suburban

    USAF-Suburban Rockstar 100 Posts

    Had the same code on and off for a while. Mine was most noticeable when after driving longer distances (more than an hour or so) and I would lose almost all acceleration. Would buck pretty bad under even the lightest acceleration. Finally had new cats put on and it cured the code and she's been running great ever since. I had a local guy put 2 universal cats on for right around $200. Hope you figure it out...

    Edit: By the way, I have a 98 C1500 5.7, with 199,600 miles.
    Last edited: Dec 30, 2013
  6. Conlan Rose

    Conlan Rose Epic Member 5+ Years 1000 Posts

    My truck currently has this code but I have yet to do anything about it. In most cases the CAT is bad or the sensor. My O2 sensor for that cat is brand new so I know its my cat and they don't come cheap in CT. In may i"m going to try to get it fixed before I need to go for emissions again.
  7. ElbowJoe

    ElbowJoe Member

    I had a PO430, PO157, PO430 over an year ago on my 03 Suburban and the truck was throwing an ABS light as well. I ended up doing a SeaFoam treatment, replacing my right downstream O2 sensor and subsequently both front ABS wheel speed sensors. (I prefer to go with the cheaper fixes first.)

    I have been error free for over a year now.

    I was happy I did not have to look at a new cat as they are very costly. I hope this is helpful.

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