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    VWVortex


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    Thread: Symptoms of Bad Temperature Sensor

    1. Member
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      2004 DBP R32
      12-22-2005 09:50 PM #1
      All this talk about the Black Top Temp Sensor vs. the Green Top Temp Sensor has got me spooked. The thread mentioned bad gas milage and rough running engine as a primary indication of the black top going bad. Are there any other symptoms that would indicate a failure of the black top sensor, like a temperature guage not moving or a hard code and CEL light? I'm still running the one that came in the car and it's running OK for now, but I was looking for a more definitive indication that it needs to be replaced.

    2. Member
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      12-22-2005 11:38 PM #2
      The only real way to determine whether your coolant temperature sensor is faulty is to use a diagnostic tool like VAG-COM to see what temperature the sensor is reporting to the ECU when the coolant is fully warm. If the reported temperature is above 180 degrees Fahrenheit or so, the sensor is most likely fine. If the reported temperature is significantly less than 180 degrees, the sensor is probably faulty.
      Kenji

    3. Member
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      2004 DBP R32
      12-23-2005 02:35 AM #3
      If the sensor is signaling significantly below below 180 will the cluster temp guage still read 190 after it's warmed up? Is this guage just for the ECU to read to adjust F/A and timing and the temp guage reads something else?

    4. Member
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      12-23-2005 11:33 AM #4
      I don't know whether the ECU and the gauge in the instrument cluster use separate coolant temperature sensors, but believe it or not, the gauge is designed to indicate 190 degrees for a wide range of actual coolant temperatures.

      Edit: removed certitude in opening clause.


      Modified by Kenji at 11:33 AM 12-23-2005

      Kenji

    5. 12-23-2005 05:34 PM #5
      Quote, originally posted by Kenji »
      The only real way to determine whether your coolant temperature sensor is faulty is to use a diagnostic tool like VAG-COM to see what temperature the sensor is reporting to the ECU when the coolant is fully warm. If the reported temperature is above 180 degrees Fahrenheit or so, the sensor is most likely fine. If the reported temperature is significantly less than 180 degrees, the sensor is probably faulty.

      i disaggree. How can you test a poss, bad sensor within the cars own electronics and trust the reading? The whole reason why the sensor may be bad is because it reports a bad reading...


    6. Member Daemon42's Avatar
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      04 R32T, 95/98 4runner
      12-23-2005 05:45 PM #6
      Quote, originally posted by ARRR Matey 32 »
      i disaggree. How can you test a poss, bad sensor within the cars own electronics and trust the reading? The whole reason why the sensor may be bad is because it reports a bad reading...

      Because the coolant temp is not regulated electronically (the thermostat
      is a mechanical device), so the coolant temp itself will tend to stay around
      190F regardless of whether the coolant temp sensor is good or not.
      So if you drive the car until you *know* it is at normal operating
      temp, and then see what coolant temp the sensor is reporting to the
      ECU, if you consistently see less than about 180F, you can be pretty sure it's faulty.

      And yes, the in dash temp gauge is mostly a placebo. It stays pointing
      straight up for a very wide rand of coolant temps and only if you're
      actually signficantly overheating or overcooling will you see it stray off
      center. So even with a faulty coolant temp sensor the in dash gauge
      may show normal.

      ian


    7. 12-23-2005 05:51 PM #7
      i smelled what seems like my car running rich on a cold starup...and a quick bouncy idle briefly..that was about it..didn't really know i had a bad one till i vag-com'd my car trying to see which one of my coilpacks failed.....really there isn't much of a way to tell without a diagnostic tool.....

      Dan

      Am I OG status yet? Close to 40 years old and still driving a slammed and Boosted 'Dub...cool or sad?

    8. 12-23-2005 06:19 PM #8
      Just curious, I have noticed that my car will idle above 1000 rpm for 30 sec or so when being started - Normal for cold temps. But sometimes, even if its zero degrees F. it idles at about 600 or so and neglects to go through the "normal" high idle warm-up phase.

      Usually will run through the high idle phase when the temps are anywhere between ~34 degrees F or higher, but not when its below 34F

      JR


    9. Member Daemon42's Avatar
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      04 R32T, 95/98 4runner
      12-23-2005 06:44 PM #9
      That behavior is normal.
      When it gets really cold, it doesn't go through the normal cold start (high idle)
      cycle. The whole high idle, rich running, air pumped into the exhaust
      manifold thing is purely for emissions. Maybe when the temp drops below
      a certain temp, they figure it doesn't matter. We don't know why, but they all
      work that way.

      ian


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