Your DS18B20 temperature sensor is likely a fake, counterfeit, clone
I&#x27;ve bought ~100 of these sensors from ali and ebay and 9&#x2F;10 had troubles reporting temperatures in passive mode reliably. However simply repeating requests until sensor reports a valid value (!=+85C and !=-127C) works fine. Rarely I&#x27;ve seen sensors not working in passive mode at all.<p>Still, I always recommend running an extra +VDC wire (3 wires vs 2 wires isn&#x27;t a big inconvenience). When running large 1-wire buses (&gt;100m long, dozens of sensors each), a dedicated power line is always a must.<p>Another funny use for these sensors is a source of nonce&#x2F;id. Weirdly, every single DS18B20 I&#x27;ve bought had a unique ROM address, even when I got large batches. I still PTSD about that batch of PCIE network cards with identical MAC addresses...