What does it mean?
OBD II fault code P0796 is a generic trouble code that is defined as “Pressure Control Solenoid “C” Performance/Stuck Off”, and is set when the PCM (Powertrain Control Module) detects a fault, failure, or malfunction that prevents the (automatic) transmission fluid pressure control solenoid labeled “C” from being cycled from the “OFF” position to the “ON” position.
Note that some advanced transmission designs may use multiple pressure control solenoids for different functions and/or purposes, and in these cases, pressure control solenoids are typically labeled “A”, “B”, “C”, “D”, and so on. Therefore, the exact function of the pressure control solenoid labeled “C” on any affected application must be determined from reliable service information. NOTE: Pressure control solenoids should not be confused with shift solenoids.
The former performs overall pressure control functions in the larger transmission, while the role of shift solenoids is limited to switching already pressurized fluid between hydraulic circuits in the valve body to enable shifts between gears. All automatic transmissions use pressurized fluid to perform functions such as engaging/disengaging clutch packs, engaging/disengaging the torque converter lockup clutch, or to alter the arrangement of planetary gear sets to effect gear shifts.
As a practical matter, the transmission fluid is pressurized by an engine-driven pump, and the flow/direction of the pressurized fluid is controlled by one or more pressure control solenoids, which are in their turn, controlled/managed/monitored by the transmission control module.
In general terms, fluid pressure control solenoids are therefore used to ensure that sufficient pressure is always available at all points in the transmission to ensure that gear shifts are performed not only smoothly and reliably, but also at predetermined shift points. Thus, given that the efficient circulation of pressurized fluid is essential for the transmission to work efficiently and reliably, it is critically important that all pressure control solenoids work as intended.
Therefore, if the PCM detects any failure, malfunction, or defect that affects the operation of the pressure solenoid labeled “C”, it will recognize that it cannot control/manage the transmission effectively, and it will set code P0796 and illuminate a warning light as a result.
It should be noted though that depending on the application and the specific function of pressure control solenoid “C”, the PCM might also initiate a fail-safe or limp mode to limit engine power as a means of protecting the transmission against damage.