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  1. #1
    Active Member One Ring
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    slow warm-up, missfire

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    my b6 takes forever to warm up and barely runs until mostly warmed up. I'm getting a P1292 map controlled thermostat and F265 open circuit codes. at the same time flashing CEL. When it reaches temp, it suddenly smooths out and the CEL stops flashing. I'm pretty sure the thermostat unit is bad, but will this cause a horrible misfire?

    Also, when replacing this thermostat housing assy, Does one have to put the radiator support in the service position? Looks like, with the alternator and throttle body removed, access should be okay....any opinions?

  2. #2
    Veteran Member Four Rings old guy's Avatar
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    Dec 28 2006
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    My Garage
    '03 A4, '13 A5, '18 MB-GLA
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    Time for a new t-stat. No need for the service position: Clicky ClickŪ

    (Thanks to Matt for the DIY from 11 years ago!!)
    A4 Motoza tuned Frankenturbo F21L / Bosch 550's / 3" MAF / TyrolSport SMIC / 034 HFC / TT 2.5" DP / Borla / Eibach ProKit / Koni Yellows / H-Sport F&R Bars / TyrolSport Brake Stiffeners / HyperShift Short Shifter / Podi
    A5 Mods to come: Little stuff so far. 20/25mm spacers / H&R OE Sport springs / 35% tint / Neuspeed Power Module / black window trim / RS grille.

  3. #3
    Active Member One Ring
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    old guy, thanks for the reply. This will cause a terrible misfire? Feels like its running on 2 cylinders until it eventually gets warm and completely smooths out!

  4. #4
    Veteran Member Four Rings old guy's Avatar
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    Dec 28 2006
    AZ Member #
    14483
    My Garage
    '03 A4, '13 A5, '18 MB-GLA
    Location
    Western Maryland

    Do your fans come on immediately when you start the engine? When the ecm can't make sense of the temperature sensor readings you get a DTC for a mapped cooling system error and the ecm takes steps to protect the engine. Like putting full power to the thermostat heater and running the cooling fans immediately. It also adjusts the fueling strategy accordingly. Consequently the ecm isn't calling for the correct A/F ratio for a cold start. Once the engine gets warmed up a little the A/F is ok and the engine smooths out.
    A4 Motoza tuned Frankenturbo F21L / Bosch 550's / 3" MAF / TyrolSport SMIC / 034 HFC / TT 2.5" DP / Borla / Eibach ProKit / Koni Yellows / H-Sport F&R Bars / TyrolSport Brake Stiffeners / HyperShift Short Shifter / Podi
    A5 Mods to come: Little stuff so far. 20/25mm spacers / H&R OE Sport springs / 35% tint / Neuspeed Power Module / black window trim / RS grille.

  5. #5
    Active Member One Ring
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    Nov 10 2018
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    Old guy, thanks again...so you feel that it's the thermostat and not one of the temp sensors on the bottom of the radiator or on the coolant elbow on the back of the engine? The fans do run when cold, and when the right temp finally shows on the gage, it never deviates from normal. If the car is shut off for a while and mostly cools, it will restart and run perfectly! The problem only occurs when stone cold.

  6. #6
    Veteran Member Four Rings old guy's Avatar
    Join Date
    Dec 28 2006
    AZ Member #
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    My Garage
    '03 A4, '13 A5, '18 MB-GLA
    Location
    Western Maryland

    Do you have access to VCDS? If so there are blocks that you can monitor to determine exactly what is wrong.

    If not, here's something you can do to help confirm whether or not the thermostat is defective. Before your next cold start unplug the thermostat heater. That would be the plug attached to the thermostat housing. If your engine heats up at the normal rate the mechanical portion of your thermostat is functioning properly. If it still takes forever to warm up your thermostat is defective.

    As I mentioned in the previous post if the ecm thinks something is wrong with the mapped cooling system it automatically goes into overheat protection mode. Stuff like turning the cooling fans on immediately and also applying full power to the thermostat heater. By unplugging the heater you take it out of the equation. Although I don't think your thermostat heater is working anyway since you have a code for an open circuit on the heater.

    EDIT: Here's a link that helps explain a bit more about how the mapped cooling system works: Clicky clickŪ
    A4 Motoza tuned Frankenturbo F21L / Bosch 550's / 3" MAF / TyrolSport SMIC / 034 HFC / TT 2.5" DP / Borla / Eibach ProKit / Koni Yellows / H-Sport F&R Bars / TyrolSport Brake Stiffeners / HyperShift Short Shifter / Podi
    A5 Mods to come: Little stuff so far. 20/25mm spacers / H&R OE Sport springs / 35% tint / Neuspeed Power Module / black window trim / RS grille.

  7. #7
    Active Member One Ring
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    Thanks again, old guy....super helpful!



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