Serial comms not reaching 0 V

Connecting a DHT22 sensor to an ESP8266, I can’t read the serial data sent back from the sensor.

I’m almost sure this is a problem with the sensor communication not reaching 0 V as the software always reads a logic 1 on the pin. If I connect it to GND, it does read a logic 0 so it’s not a port problem.

How can I make it reach 0 V? Where is this offset voltage coming from?

PD: This doesn’t work with any DHT22 library for Arduino, nor with my FreeRTOS code.

PDD: I’ve tried using an external 10K pull-up and the internal pull-up from the ESP8266.

EDIT:

^{simulate this circuit – Schematic created using CircuitLab}