Downshifting on a slippery road may cause vehicle instability because the engine braking may lock up the wheels. When engine braking begins to cause the wheels to lock up, the engine drag torque control commands the PCM to increase the torque, helping to prevent tire slip.

The VSA modulator-control unit calculates the vehicle speed and acceleration of each wheel from each wheel speed sensor signal and makes judgment on the slip condition of the wheel. The VSA modulator-control unit adjusts the engine torque based on the slip condition.