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2004 GMC Envoy - SES light

Discussion in 'Member Introductions' started by rbruno303, Oct 21, 2009.

  1. rbruno303

    rbruno303 New Member

    I have a 2004 GMC Envoy since 0 miles. Can someone please help me understand why the "Service Engine Soon" light comes on and then it goes off?
    I replaced the fuel cap, because that was the first problem I had years ago, but now the same light shows up.
    I went to the dealer and they found a P0128 code. According to them, I need to replace the thermostat for a $300 (because they need to remove the alternator).
    I don't believe that's the problem. Have somebody any advice, or have had a similar problem?
    I will appreciate any help...

  2. Jimmiee

    Jimmiee New Member 1000 Posts

    Your PCM monitors all your Powertrain inputs including your engine temperature. If the engine temperature is low after a predetermined length of time the PCM assumes the thermostat is stuck open. If the engine temperature is indeed low the most likely cause would be a defective thermostat. Another possibility would be a defective engine temperature sensor. Does your heater get hot immediately and stay hot or is it just lukewarm?
  3. retired2001

    retired2001 New Member 1000 Posts

    Welcome to the site!
  4. ct9a

    ct9a New Member 1000 Posts

    Welcome to the site!
  5. Eddie Z71

    Eddie Z71 Active Member 1000 Posts

    Welcome to the site!:great:
  6. canislupis69

    canislupis69 New Member 1000 Posts

    Welcome to the site!
  7. GMPartsClub

    GMPartsClub New Member GMTC Sponsor

  8. rbruno303

    rbruno303 New Member

    I having trouble filling the gas tank

    Also, besides SES came on (P0128), it takes 10 to 15 minutes to fill the gas tank because the nozzle continues to shut-off (like it is full) and I know it is not.
    I believe there is a Relation between P0128 and filling up gas tank
  9. rbruno303

    rbruno303 New Member

    I didn't try the heater yet...but please read my last post.. I'm also having problem filling the gas tank....
  10. Jimmiee

    Jimmiee New Member 1000 Posts

    I don't think the code is related to filling the tank. There is either some obstruction in your filler neck or the vent hose that goes from the top of the tank to the top of the filler neck is plugged up.

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