What does it mean?
If your vehicle has exhibited an illuminated malfunction indicator lamp (MIL), and has stored a code P0961, it means that the powertrain control module (PCM) has detected a problem with a specific electronic pressure control solenoid (EPCS) or solenoid circuit for the automatic transmission. The designation A usually refers to the primary EPCS/circuit. This code is used exclusively in vehicles equipped with automatic transmissions.
Automatic transmissions in OBD-II vehicles are controlled electronically by the PCM or a stand-alone controller, called a transmission control module (TCM). Most transmission controllers are integrated into the PCM.
The major components of the transmission control system are: Control module Controller area network (CAN) Numerous sensors and solenoids A powerful hydraulic pump One or more electronic pressure control solenoid/s An assortment of shift solenoids A torque converter clutch solenoid A hydraulic valve body The transmission controller receives input signals from various engine and transmission sensors.
Engine sensor inputs typically include the degree of throttle angle, engine RPM, engine coolant temperature, and engine load percentage. Transmission sensor inputs are designed to monitor transmission input speed (RPM), transmission output speed (RPM), shifter position, torque converter lock-up percentage, vehicle speed, transmission temperature, and pump pressure. This is not an exhaustive list.
These input signals are used by the transmission controller to aid in mapping shift strategy and electronic pump pressure parameters. The electronic pressure control solenoid/valve (usually located in the valve body) is used to regulate pump pressure. Careful regulation of pump pressure keeps the transmission shifting smoothly and precisely. Maximum pump pressure - applied directly to the valve body - would lead to extremely harsh shifting and potential driveline damage.
If the PCM detects that it cannot regulate pump pressure (by applying the appropriate degree of voltage to the EPCS) or detects a level of EPCS circuit voltage/resistance that is not within programmed specifications, a P0961 will be stored and a MIL may be illuminated.