What does it mean?
In an automatic transmission, gears are changed based on variances in pressure through the valve body. Pressure changes were modulated by spool valves previously, but on modern transmissions, spool valves have been replaced in large part with solenoid valves. These solenoid valves are activated by the module that controls transmission shifts, typically the transmission control module (TCM) or the engine control module (ECM).
When the gearshift position is changed, the TCM activates solenoid valves so the transmission can operate specific gears. For each gear that’s selected, there can be one or many solenoid valves that are activated, and as the gears change solenoids are deactivated and others activated. The specific sequence that solenoid valves operate varies depending on the manufacturer. Each transmission manufacturer uses solenoid valves in different combinations based on their individual design.
However, if code P0997 is present, the transmission will contain shift solenoid F, or SSF on the valve body in some form. Shift solenoids are numbered alphabetically, so shift solenoid F indicates there are at least six shift solenoids on the valve body. While the transmission is operating, the TCM checks each solenoid valve’s operation. If SSF fails its check more than twice in an ignition cycle, DTC P0997 is set in the TCM.