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I have a 2004 Sienna with 380K miles. While the engine is hot, I can hear the radiator fans running as I come to a stop light but as soon as I come to a complete stop the fans will go off. If I sit in a drive through or leave the van running while parked it will start to overheat. Otherwise it’s fine, I’m 100% the fans are fine and they only come on when the temperature is high. So temp sensor must be good. What would cause them to stop at idle only. Thanks
 

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2015 Sienna / 2018 RAV4
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How's your system voltage? Does it drop below 12.5 or so when your van is at a standstill? I'm thinking a microcontroller is sensitive to low voltage. Could indicate an alternator / voltage regulator issue, or even a questionable battery.

The fan microprocessor controller is between the fans on the center radiator mount. Powering that, IIRC, is a cube relay in the fuse box next to the battery. Check inputs and outputs of these components to track down your issue.
 
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