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Thread: P0128 and a few other minor problems.

  1. #1
    phigment is offline Cadillac Owners Fanatic
    Automobile(s): DTS
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    P0128 and a few other minor problems.

    Awhile back I had problems with my car overheating. I replaced the thermostat and the problem seemed to be fixed. Then I had a problem with P0420 indicating I had a failing Catalytic Converter. I cleared the P0420 and it has not returned. Also my temp gauge stopped working. The needle would not move for a day or so and then it would start working again. I purchased a scantool in an effort to better understand what was going on here. My gauge stopped working again this morning. I drove the car to work and plugged my scantool in. My engine temp reading was 182 degree F and I had a code P0128. Could I have installed a bad thermostat? Also I did replace the temperature sensor. The new sensor, as far as the gauge goes, reports the same as the old sensor. As always, thanks guys.


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  3. #2
    Superjim's Avatar
    Superjim is offline Cadillac Owners Connoisseur
    Automobile(s): 2011 DTS Platinum
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    Re: P0128 and a few other minor problems.

    Did you use a real OEM thermostat or a different brand from the auto store...
    Sometimes the other brands of t-stats do not work well in the Northstar...
    Believe it or not... LOW COOLANT can also cause this code...
    Last edited by Superjim; 03-02-13 at 09:07 AM.

  4. #3
    phigment is offline Cadillac Owners Fanatic
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    Re: P0128 and a few other minor problems.

    It wasn't OEM. I checked my coolant. The reservoir is over half full. Ill hit the dealership on Monday and pick up an OEM thermostat. Would that cause the temp gauge not to work?

  5. #4
    Superjim's Avatar
    Superjim is offline Cadillac Owners Connoisseur
    Automobile(s): 2011 DTS Platinum
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    Re: P0128 and a few other minor problems.

    Quote Originally Posted by phigment View Post
    It wasn't OEM. I checked my coolant. The reservoir is over half full. Ill hit the dealership on Monday and pick up an OEM thermostat. Would that cause the temp gauge not to work?
    It shouldn't affect the temp gauge at all... unless it is just running really cold and not getting hot enough to make it move.
    Be EXTRA SURE you put the thermostat in the CORRECT WAY... it can be put in upside down and will not function correctly.

    Disconnect both battery terminals... negative cable FIRST... touch them together for a few seconds to discharge all the capacitors in the car.
    Hook them back up.. Negative one LAST...
    See if your temp gauge now works.


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