-40 on ECT and code P0420 Catalyst Efficiency 2004 XC70
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    1. #1
      Junior Member
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      -40 on ECT and code P0420 Catalyst Efficiency 2004 XC70

      Was hoping fresh coils would clean up a nagging P0420 code on this 2004 XC70 in our fleet, 180 K miles, but apparently not.

      It set not one, but two P0420 codes after being driven in heavy rain yesterday.

      The odd thing is the freeze frame data on both codes showed ECT (engine coolant temp) at -40 that seems like maybe a bad sensor, or wiring?

      Or maybe Volvo doesn't report accurate ECT's on generic code readers?

      Has anyone encountered this?
      Last edited by zak; 11-25-2019 at 08:57 AM.

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    3. #2
      Senior Member ScottishBrick's Avatar
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      If the ECT was that far out it wouldn’t run.

      I’d just space the rear o2 sensor.
      2003 V70 T5 - Mystic/Graphite - M56LK - 195k - "O-Three"
      1999 V70 T5 - Pewter/R Graphite & Alcantara - AW42 - 291k - Daily/Work Wagon
      1999 V70 T5 - Nautic/R Graphite & Alcantara - M56H - 174k - Rescued
      1999 V70 T5 - Emerald/Graphite - M56H - 119k - Garage Queen
      2000 V70 T5 - Mystic/Graphite - AW42 - 238k - Moms Unicorn
      2000 S70 GLT SE- Mystic/Graphite - AW42 - 212k - Sisters

    4. #3
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      Wonder if its having some sort of periodic fault, though think you would feel it in the engine. ECM sees momentary ultra cold engine adds fuel and that causes the catalyst efficiency to drop.

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    6. #4
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      At least get a Volvo-specific OBD-II scanner, if not DiCE/VIDA. It's too frustrating owning one of these Volvos without this tool.

    7. #5
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      If both 02's and the ECT are originals at 180 thou replace all 3. They are all over due. FCP probably has a good Black Friday deal.

    8. #6
      Junior Member
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      -40 degrees on an ECT means there's an open circuit.
      2007 S40 T5

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