What does it mean?
OBD II fault code P061B is a generic trouble code that is defined as “Internal Control Module Torque Calculation Performance”, and is set when the PCM (Powertrain Control Module) and/or one of several other control modules detects a difference between the actual and desired engine torque value. Note that the engine torque value is a critically important parameter that affects not only the transmission control system but also safety systems like traction and stability control, among others.
All modern vehicles use a sophisticated system to control, monitor and manage the amount of power an engine develops throughout its operating range. This process runs continuously, and while the PCM represents the pinnacle of the control/management hierarchy, all control modules that either assist in monitoring engine torque, or whose correct functioning depends on engine torque being reported accurately, can set both this particular code, and several other, closely related codes.
As a practical matter, torque control is important to a) make gearshifts both comfortable and predictable, b), to ensure the correct functioning of stability and traction control systems, and c), to protect driveline components against damage caused by excessive torque being developed at inappropriate times.
Nonetheless, The PCM and other implicated control modules monitor input data from engine sensors such as the Mass Airflow Sensor, Absolute Manifold Pressure Sensor, Throttle Position Sensor, Throttle Pedal Position Sensor, Intake Air Temperature Sensor, and others that may include the Engine Coolant Temperature Sensor and Transmission Fluid Temperature Sensor.
This information is shared among all implicated control modules via the CAN (Controller Area Network) serial communications system during both normal vehicle operation, and when the ignition is turned on. When the ignition is turned on, all implicated control modules are forced to perform a series of self-diagnostic tests, and to communicate their status (healthy, or otherwise) to all other control modules to confirm the integrity of the larger torque control system.
However, when the vehicle starts to move, the PCM and various other control modules monitor the actual torque value being developed. While the code setting parameters differ between applications, code P061B will typically set when the actual and desired torque values differ by more than about 50 Newton meters for longer than 1 second at engine speeds above 5000 RPM, or when the engine’s volumetric efficiency is higher than about 16%.
When one or sometimes both enabling conditions are met, the PCM and/or another control module will recognize that the engine’s torque cannot be controlled or managed effectively, and one or more control modules will set code P061B and illuminate a warning light as result. Note that depending on the application and the exact nature or severity of the problem, the PCM may also initiate a fail-safe or limp mode as a safety precaution.
Note also that depending on the application, code P061B may not set on the first failure; in some cases, as many as eight consecutive failures need to be recorded before this code will set.