Electrosurgical systems and methods are described herein, the system including an electrosurgical probe with an active electrode disposed near the probe distal end, a system with a power supply for delivery of voltage to the active electrode and a controller that receives and processes a signal from a current sensor and a temperature sensor. The current sensor measures the current output of the power supply and the temperature sensor is adjacent an electrically conductive fluid located at a target site. The controller may be programmed to operate in a low voltage mode that limits the power supply to a low voltage output so as to determine whether the current output from the current sensor is within a current output range. This range is defined by predetermined upper and lower limits that are modified by at least one measured value.