The P0697 OBDII diagnostic code is set because the PCM (Powertrain Control Module) has found an open circuit on a specific sensor, which is designated as C. This sensor is related to the automatic transmission. To determine the location and function of the sensor, you should consult the vehicle’s information source.
The reference voltage is usually 5 volts, and it is applied to the sensor through a switched circuit. This sensor referred to in the code must also be grounded and its resistance is variable.
An input voltage signal is delivered to the PCM because the resistance of the sensor changes with some conditions. If the PCM fails to receive this input signal, the circuit is considered open, and the Check Engine light illuminates next to this code.