I have a fair bit of Microchip experience, things to consider: - You must set the AD1PCFGH or ANSEL bits to enable ADC functionality on a pin. - There's nothi

I have a fair bit of Microchip experience, things to consider: - You must set the AD1PCFGH or ANSEL bits to enable ADC functionality on a pin. - There's nothing stopping you from accidentally configuring the pin as a digital output (it might even be helpful for some applications to measure the actual output from a digital output). Check the value of the TRIS register for that pin (and ODC register if it has it) - Often there is a "Configuring Analog Port" section in the I/O Port section of the chip's datasheet. Good luck!