What does it mean?
In the modern automatic transmission, hydraulic pressure is generated in the pump, usually located at the front of the transmission, driven by the engine via the torque converter housing. Channels direct automatic transmission fluid to the valve body, which contains the shift solenoid (SS) valves and pressure control solenoid (PCS) valves. The transmission control module (TCM) controls the activation and modulation of the various solenoid valves, depending on driver demand and driving conditions.
The TCM may or may not be integrated into the ECM (engine control module). Electronically-controlled valves are used to shift and maintain gears. The SS valves control the activation and deactivation of clutches, brakes, and bands inside the transmission, effecting the engagement and disengagement of whatever gear is desired or required by the driver and operating conditions.
One or more PCS valves control hydraulic pressure inside the transmission, which can affect how shift engagements occur, whether slow and soft or hard and fast. If the TCM detects a problem with one of the valves, such as a short circuit, it commands the malfunction indicator lamp (MIL) “On” and stores a diagnostic trouble code (DTC) in system memory. DTC P0966 is defined as “Pressure Control Solenoid ‘B’ Control Circuit Low,” though different automakers may have slightly different definitions.
Note: Circuit Low Input codes are often the result of low battery voltages (that can have many possible causes), bad connections across electrical connectors or previously repaired wiring, as well as corrosion in electrical connectors.
Other possible causes of low input voltages include poor installation of aftermarket components, poor quality aftermarket components like fuses, relays, and switches, and modification of the electrical system that could include the use of conductors that are not rated for use in a particular application. However, poor connections often result in high resistances in some parts of the circuit, which is why it is important to perform resistance and continuity checks during the diagnostic procedure.