What does it mean?
OBD II fault code P0741 is most commonly defined as “ Torque Converter Clutch Circuit Performance” or sometimes as “Torque Converter Clutch- Stuck Off”, and is set when the PCM (Powertrain Control Module) detects an abnormal electrical value in the torque converter clutch control circuit.
The words “Stuck Off” in a definition of this code refers to the fact that the torque converter clutch control solenoid is stuck in the “OFF” position, and can therefore not engage the torque converter clutch or lock-up mechanism.
Although the actual parameters that set code P0741 vary greatly between applications, the basic operating principles and purpose of the torque converter clutch remain the same in all cases, which is to provide a solid link between the engine and the transmission, much like a conventional clutch locks a manual transmission to the engine.
By locking the transmission to the engine, all slippage in the torque converter is eliminated, which increases engine power delivery to the driving wheels, and improves fuel economy. In terms of the system’s operation, the PCM gathers information from various sensors such the throttle position sensor, vehicle speed sensor, transmission turbine speed sensor, engine speed sensor, boost control sensor, and others to determine the degree to which the engine must be locked to the engine.
The lock-up function is accomplished by solenoids that control the flow rate, and hence the usable pressure of pressurized transmission fluid to vary the amount of converter lock-up.
However, to prevent engine torque from overcoming the shear strength of the transmission fluid in the torque converter, or to prevent excessive torque from damaging transmission or other drivetrain components, the system is also designed to allow some slippage to occur under certain conditions, such as severe acceleration. “Shear strength” refers to the transmission fluids’ ability to transmit torque from the drive, to the driven side of the torque converter; when the fluids’ shear strength is exceeded or overcome, the torque converter is said to “slip” and some of the engine power is lost to the drivetrain as a result.
The pressure required to accomplish converter lock-up derives from the transmission’s integral pressure pump that is driven by the engine via the torque converter. Based on inputs from the PCM, some of the pressure is directed through either solenoids or valve shuttles in the valve body to activate the actual torque converter lock-up mechanism.
When the PCM detects a difference between the actual amount of lock-up and the amount of lock-up it expects to see given reigning operating conditions, a code will be set. Depending on the application, a warning light may or may not be triggered, since some applications require more than one failure cycle to occur before triggering a warning light. The image below shows a simplified schematic of a typical torque converter that incorporates a clutch/lock-up mechanism.
Note the flow path the transmission fluid takes to activate the clutch.