Can a O2 sensor failure cause a Cat code?

Discussion in 'General Chevy & GM Tech Questions' started by Bredin, Mar 3, 2009.

  1. Bredin

    Bredin Rockstar


    I took my 99 burban to get it inspected today.

    FAILED lol... check engine light was out, and they plugged the OBDII reader into it.

    Came back with
    P0161 (O2 Sensor Heater Circuit Bank 2 Sensor 2)
    P0420 Catalyst System Efficiency Below Threshold Bank 1
    P0430 Catalyst System Efficiency Below Threshold Bank 2

    Could the problem with the O2 Sensor cause the code for the Cat to show or do I have to replace the cats ?
  2. Jimmiee

    Jimmiee Epic Member 5+ Years 1000 Posts

    Yes it sure can. The O2 sensor before the cat measures the Hydrocarbons before the cat and the Downstream O2 "sees" if the cat is working. A bad upstream sensor can cause the cat code.
  3. Bredin

    Bredin Rockstar

    Correct me if I am wrong, but isnt Sensor 2 Bank 2 the O2 sensor on the passenger side, after the cat, no before the cat?

    Also, the 99 Suburban (K1500 with R motor, 350) doesnt it have two cats?
  4. Z71_guy

    Z71_guy Epic Member 5+ Years 1000 Posts

    I believe your right about the location of the O2, if the truck is the old body style 99' with the 5.7 there should be two cats(my 97 did and its the same motor)
  5. Bredin

    Bredin Rockstar

    Yup, old body style, not the rounded one with less interior room :) and the 5.7L...

    So I guess I should go with new cats uh :(
  6. Jimmiee

    Jimmiee Epic Member 5+ Years 1000 Posts

    I didn't realize it had 2 cats. I would still make sure the O2 sensor is working correctly before changing the cats.< jmo>
  7. Bredin

    Bredin Rockstar

    Yup, gonna do that first too.... new O2 sensor is $65 with lifetime warranty... cat is alot more lol
    but I think I can get it at the junkyard for free :x
  8. mjalstad

    mjalstad Rockstar 100 Posts

    You could try swapping the O2 sensors and see if the code moves over to the other bank. If it does, then you know you need an O2 sensor, if not then you may want to get a new cat.
  9. daddytech

    daddytech Epic Member 5+ Years 500 Posts

    Run some Sea Foam through it. couple cans of that stuff run through the vaccuum line on your power brake booster then mildly rev the truck once the white smoke starts coming out the tail pipe and keep doing it until the white smoke stops. My wife's suburban was throwing O2 sensor codes and the Cat code too. one can of Sea foam and about 15 minutes later, she was running smooth with no codes at all.
  10. daddytech

    daddytech Epic Member 5+ Years 500 Posts

    I own a 99 tahoe and there is only one cat on it there are however 4 O2 sensors on it. There are 2 in the upper part of the exhaust and 1 on each side of the muffler pipe just before it joins and makes the turn to go to the cat. there are no sensors after the cat what would be the point in that ???

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