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Thread: P 0420 code.... in a 2007 CTS (old thread)

  1. #1
    99supersts is offline Cadillac Owners Member
    Automobile(s): 99 STS
    Join Date
    Aug 2010

    P 0420 code.... in a 2007 CTS (old thread)

    is a p0420- catalyst system low efficiency. is this code pretty much limited to just having a bad cat? or is there any other possibilities that will throw this code? the cat isnt too old..replaced 2yrs ago.. i was driving today maybe 15mins into the drive, and stopped at a red light and while idling the light came on.. got home and cleared the code so far it hasnt come back on yet.. i did just add a bottle of lucas " tune up in a bottle" to my last tank of gas so not sure if that may have caused it..

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  3. #2
    6SENSE is offline Cadillac Owners Member
    Automobile(s): 2007 CTS
    Join Date
    Feb 2013

    Re: p0420 code....

    I see this is an really old post but met my search criteria and didn't know if you ever found out anything out (I assume you had to have). I added about 7 ounces of Lucas (from big bottle) into low tank before fill-up yesterday. Parked the car and then later jumped on road with kids for >200 mile roadtrip. Shortly after leaving (maybe 20 minutes) P0420 popped up. Hasn't gone away. Car seemingly drives fine but efficiency/gas mileage has taken a hit. Lucas/P0420 maybe just a coincidence?
    I've used this fuel cleaner for years with various vehicles.

  4. #3
    Submariner409's Avatar
    Submariner409 is offline If it won't run, stick on fender vents
    Automobile(s): 2002.5 F55 STS - 66500 miles, 2014 Explorer XLT FWD
    Join Date
    Feb 2006
    MD Eastern Shore, Kent Island

    Re: p0420 code....

    Let's move this from Seville to the proper CTS forums - there are some pretty knowledgeable guys there.

    - and fuel cleaners are not needed - Google "chevron techron" for a look at a one-time powerful fuel system cleaner and also look at "top tier gasoline".

    P 0420 is low cat efficiency - can you do foot-on-the-floor acceleration to redline in 1st, 2nd, maybe 3rd with no hesitations, bogging, power loss throughout the rpm range ? (I see you now have some driveability problems)

    Personally, I would never put Lucas-anything in a dead Briggs&Stratton lawnmower much less my car or trucks.

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