What does it mean?
OBD II fault code P0755 is a generic code that is defined as “Shift solenoid (SS) B -circuit malfunction”, and is set when the PCM (Powertrain Control Module) or TCM (Transmission Control Module) detects an electrical malfunction either in the transmission shift solenoid labelled “B” itself, or in the “B” solenoid’s control circuit. All automatic transmissions use computer controlled solenoids to shift pressurized transmission fluid between hydraulic circuits to accomplish gear shifts.
Regardless of the number of gear ratios any given transmission has, each gear shift is accomplished by a shift solenoid that is dedicated to one gear ratio. While some older transmissions may have only four shift solenoids labelled “A”, “B”, “C”, and “D”, newer transmissions usually have more ratios, with the additional shift solenoids labelled “F”, “G”, and “H”, for a total of seven shift solenoids.
In practical terms, when a gear shift is initiated, the solenoid that controls the next higher or lower gear is energized by the PCM/TCM. This action redirects pressurized fluid into the hydraulic circuit(s) that controls the selected gear ratio.
Thus, when a particular hydraulic circuit is pressurized, all the transmission components that select and maintain that gear are moved into position in a series of events that is roughly analogous to the way different combinations of gears are selected to establish different gear ratios in manual transmissions.
Therefore, when the PCM/TCM detects a malfunction in the control circuit of shift solenoid “B”, the controller can no longer control gear shifts efficiently, and code P0755 will be set and a warning light may be illuminated as a result. The image below shows the typical arrangement of transmission shift solenoids.
In many cases, shift solenoids are not accessible from outside of the transmission, which means that the transmission oil pan has to be removed to access individual shift solenoids, internal wiring, or to a shift solenoid pack that can only be replaced as a complete unit. Note that the arrangement of shift solenoids varies greatly between manufacturers; refer to the manual for the affected application to determine the exact location of shift solenoid “B” relative to other components.