CTS-V O2 sensors
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2004-2007 Cadillac CTS-V General Discussion Discussion, CTS-V O2 sensors in Cadillac CTS-V Series Forum - 2004 - 2007; Ok, this is my first post, but have gotten LOTS of info off this forum in the past, so first ...
  1. #1
    lollygagger8's Avatar
    lollygagger8 is offline Cadillac Owners Connoisseur
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    CTS-V O2 sensors

    Ok, this is my first post, but have gotten LOTS of info off this forum in the past, so first and for most...thank you to all!!!

    I was wondering if it's more important to replace the UPstream (before cat)
    O2 sensor, or the DOWNstream (after cat) O2 sensor. I'm sure the answer is both are important, but I'd like to see which one should I do first? I don't have a problem doing them at seperate times.

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    urbanski is offline Cadillac Owners 10000+ Posts
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    Re: CTS-V O2 sensors

    why? you have codes? the code says which one is bad

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    lollygagger8's Avatar
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    Re: CTS-V O2 sensors

    The handheld computer reader said it was running lean...I didn't get a code. (it was a small snap on reader, and it wasn't mine or done by me, I was looking over the mechanic/tuners shoulder..I was talking to him about getting a computer upgrade) I assume that means O2 sensor, or vacuum leak? I had the computer reset so the engine light went off, but it's only been 50 miles or so. Aren't you supposed to replace O2 sensors every 30k miles?

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    heavymetals's Avatar
    heavymetals is offline Cadillac Owners Master
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    Re: CTS-V O2 sensors

    Check for a leak first.

    If your really cheap, swap sensors and see if the failure/code follows it.

  6. #5
    lollygagger8's Avatar
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    Re: CTS-V O2 sensors

    Anybody found a way to pull the engine cover off without taking the strut tower brace off? I know I'm asking for the world here.....

  7. #6
    urbanski is offline Cadillac Owners 10000+ Posts
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    Re: CTS-V O2 sensors

    wait, you had a CEL but no code? that wont happen.
    and no, they are not standard replacement items and have a specific code when bad

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    StealthV's Avatar
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    Re: CTS-V O2 sensors

    The strut brace must come off to get the engine cover off in one piece.

    It's all ball bearings these days.

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    Re: CTS-V O2 sensors

    The downstream (after cat) O2 sensors are super easy to get to from underneath...no biggie. How do you get the top ones (before cat) out? Is going in from the top of the engine easier?

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    The Tony Show's Avatar
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    Re: CTS-V O2 sensors

    The after-cat sensors do nothing but monitor catalyst efficiency- if one of them was bad, the code would be for "Poor catalyst efficiency".

    I wouldn't assume the sensor is bad, since that will usually throw a "Low circuit voltage" code. Chances are you have a vacuum leak or fuel issue that's causing the lean condition. Has the car been tuned?
    Rest in Peace, J.D. (aka Dirt_Cheap_Fleetwood)

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    Re: CTS-V O2 sensors

    Car hasen't been "tuned" yet....I was waiting to install the xpipe first (which that was done last night) I will check for a vacuum leak first. I've always heard you should replace your O2 sensors every 30k. Has anyone replaced their's yet? Should I go in from top of bottom of the engine?

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    ewill3rd is offline Cadillac Technician
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    Re: CTS-V O2 sensors

    Don't replace O2 sensors for lean exhaust codes.
    A very tricky set of circumstances would have to arise to have bad O2s and not set codes for sensors but set codes for lean exhaust.
    Find the vacuum leak or the induction system leak and fix it.
    Be sure to look over the air inlet from the MAF to the engine. Sometimes those come loose, especially if you have a CAI.
    That will set the code also.

  13. #12
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    Re: CTS-V O2 sensors

    I will definitely check the air inlet to the CAI and check the MAF to see if it's loose. THANK YOU SO MUCH ewill3rd! Do you agree on changing the O2 sensors every 30k? I already bought the upstream ones, just haven't put em in yet.

  14. #13
    jr_vette is offline Cadillac Owners Member
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    Re: CTS-V O2 sensors

    Newer O2 sensors are good for 100K miles. If it's reading lean, you can be pretty much guarenteed that bank is running lean.

    The sensors behind the cat's ensure that the pre-cat sensors and cat converters are working efficiently. This is mainly for emissions, and really serves no purpose on the air/fuel functions of the engine controls.

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    Re: CTS-V O2 sensors

    The rear O2 are for smog purposes and fronts are for performance/engine operation purposes. So fronts are important to me and I won't swap out the rears unless there is a reason for it.

    And what do you mean by lean? Are you talking LTFT or STFT? Which bank? Because of the weather, altitude, & other environmental variables, the car will never get 0% LTFT (not lean or rich) in all the cells. I would only swap out O2's if I know for sure they are way off or lazy at switching from lean to rich.

  16. #15
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    Re: CTS-V O2 sensors

    So say I fix the vacuum leak (assuming there is one) am I going to need a new tune to get it to run richer/correctly, or what? I've been planning on geting it "tuned".....

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