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Thread: Thermo fans

  1. Default Thermo fans

    I have some queries about engine cooling. I am repairing a few things on my car (A4 B6 2.0l) and have not driven it yet but start and run the engine in idle. After a while the temp gets to half way (90deg) but the fans still not kicking in. While is at 90 deg when I turn the engine off and then just turn ignition on, the fans start for about 5 seconds and then stop. But they never come on while the engine is running.
    When I run diagnostic I get this error:
    17700 - Map Controlled Engine Cooling Thermostat (F265): Open Circuit
    P1292-004 - No Signal/Communication

    Doing a google search it is to do with the thermostat / thermostat wiring / fuse.

    I would really appreciate if someone was able to answer:
    What triggers the fans - temp in the engine or temp in the radiator?
    If you have the same model car, at what temp do the fans start??
    If the thermostat was faulty why would that prevent the fans from running?
    Why would fans come on for 5 sec when ignition is on?

    Thanks in advance
    Last edited by TEguy; September 5th, 2018 at 12:47 AM.

  2. #2


    CTS is probably faulty.
    I expect it uses the same sensor as the B5/C5/D2 era cars, which is a common failure item.
    It provides 2 separate signals, one to the gauge, and one to the ECU.

    You haven't said if it overheats? Though with the 'idiot gauges' on modern Audi's, it would be at about 105 or so before registering over 90.

    Worth checking for a radiator mounted switch too, though if its ECU controlled, I doubt it has one.

    HVAC will trigger fan operation too.
    Last edited by 27litres; September 5th, 2018 at 06:45 PM.

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  3. The Following User Says Thank You to 27litres For This Useful Post:

    TEguy (September 6th, 2018)

  4. Default

    Thanks Marty,
    Is it possible that it is faulty but still provides some signal??
    What I could see while testing is the temp gauge moving a bit quicker than the reading on VCDS on my laptop. By the time gauge went to 90 deg, VCDS reading was 80 deg. Then the temp gauge just sat at 90 for ages, while the VCDS reading continued to gradually increase. By the time VCDS went to 99 deg, the gauge was still sitting at 90 and fans still not starting. At that point I shut it off.

    The only error I find in diagnostic is as mentioned before
    17700 - Map Controlled Engine Cooling Thermostat (F265): Open Circuit
    P1292-004 - No Signal/Communication

    And yes, there is another temp sensor at the radiator outlet.

    And like you mentioned, when I turn on air cond, the fans come on as they should, so wiring / fan module should be ok.

    Looks like I need to replace temp sensor or thermostat gismo or both.

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