1998 STS Trouble Codes & Emission Test

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Northstar Engines and System Technical Discussion Discussion, 1998 STS Trouble Codes & Emission Test in Cadillac Engine Discussion; What's up fellas. I'm on my second 7 day permit to drive on while I try to pass emissons test. ...
  1. #1
    Dastro79's Avatar
    Dastro79 is offline Cadillac Owners Member
    Automobile(s): 1998 Cadillac Seville STS
    Join Date
    May 2012
    Chicago, IL.

    1998 STS Trouble Codes & Emission Test

    What's up fellas. I'm on my second 7 day permit to drive on while I try to pass emissons test. I've reset the computer since I had the car the past year atleast 20 times just to et the engine light out. However I know that doesn't fix the problem. I have about 3 codes that are current. I'm not around the vehicle right now so bare with me.....the engine light pops on & I get P0440(EVAP) along with "Check Gas Cap"
    Another code I believe is for the speed sensor.
    And another is for the door vent actuators. I will post those other 2 exact codes but the one that concerns me is P0440 & check gas cap. Those maybe preventing me frm passin emissions. Help anyone please?

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  3. #2
    Ranger's Avatar
    Ranger is offline Cadillac Owners Member
    Automobile(s): White Diamond '03 DHS (with DTS floor shift)
    Join Date
    Jun 2004
    Woodstock Ill.

    Re: 1998 STS Trouble Codes & Emission Test

    It's the P codes that will cause you to fail the emissions test. P0440 is telling you that you have a vacuum leak in the EVAP system. A bad or poorly seated gas cap is a common cause, hence the "Gas Cap" message. Check all the lines and fittings.


  4. #3
    Submariner409's Avatar
    Submariner409 is offline If it won't run, install a boombox
    Automobile(s): 2002.5 F55 STS - 67,500 miles, 2014 Explorer XLT FWD
    Join Date
    Feb 2006
    MD Eastern Shore, Kent Island

    Re: 1998 STS Trouble Codes & Emission Test

    ANY EVAP code will fail an emissions test. EVAP is the system that stores fuel vapor from the fuel in the gas tank expansion/contraction due to heat/cold. The system uses sensors, solenoids, lines, and a charcoal canister to store vapor until the engine is warmed up and at some steady cruise operating condition - then the EVAP syatem purges the charcoal canister with fresh air, burning the stored fuel vapor in the process.

    The problem can be with a gas cap, filler neck, vacuum lines, canister, solenoids, or pressure sensor(s). P 0440 says that you have an air/vacuum leak into the sealed system - somewhere.

    Oooopppppssss........... Ranger beat me.

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