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Heater only works when moving blows cold air when stopped or idling

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These vehicles have a mapped cooling system which will turn on the cooling fans. The fans will run continuosly from around 3 minutes after starting the engine. Do your fans run continuously? –  Allan Osborne Dec 11 '13 at 20:57
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2 Answers

Several Possibilities

  • Low Coolant Level
  • Partially plugged up heater core
  • Partially obstructed heater valve
  • Weak water pump
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A faulty, always open thermostat or a defective radiator temperature sensor would cause the symptoms you describe. When your cooling system sensors send implausible signals to the engine ECU, the ECU turns the fans on to run continuously soon after start-up. The thinking is that an engine running cooler is preferable to an engine being allowed to overheat.

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