What does it mean?
OBD II fault code U0124 is defined as “Data bus: Lateral Acceleration Sensor Module – no communication”, and is set when the PCM (Powertrain Control Module) does not receive any communication from the lateral acceleration sensor via the ABS/ESC control module for a predefined period of time. Note that depending on the application, the time needed for communication to be lost before the code sets varies.
Typically though, an interruption in communication of once in about 5 seconds will set the code on most applications. On vehicles that are fitted with electronic stability control, the function of the lateral acceleration sensor is to detect accelerations that deviate from the line set by the steering angle. When the steering wheel is turned, the steering angle sensor communicates the steering angle to various other sensors, including the lateral acceleration sensor and the ABS controller.
If the vehicle is operated normally, the vehicle will follow the line dictated by the front wheels; however, should the cornering forces exceed the abilities of the vehicle to cope with those forces, the accelerations detected by the lateral acceleration sensor will trigger the ABS system to apply braking forces to the wheels selectively to force the vehicle to follow the line dictated by the steering angle.
In practical terms, the lateral acceleration sensor measures sideways movements of the vehicle, and should a potentially dangerous situation arise, the ABS brake system is activated autonomously to prevent a vehicle from entering a slide or skid- sometimes even before the driver realizes that a dangerous situation is developing.
In practice, the ABS system is used to slow the rotation of selected wheels, thus serving as “anchors” around which to pivot the vehicle to maintain stability during evasive manoeuvres or emergency braking. Note however that the lateral acceleration sensor is programmed to assume that the vehicle is in good mechanical condition. It cannot detect bald tires, worn suspension components, or compensate for reckless driving.
Therefore, since no safety system can overcome the laws of physics, an over reliance on the stability control system should be avoided. The image below shows the typical configuration of a stability control system, with reference to all the other main sensors and controllers that are involved in making the system work. Note the location of the lateral acceleration sensor in this application.
This is only one possible location for this sensor; locations differ widely, and it could be anywhere from under the dashboard, to under any of the seats. Consult the manual for your vehicle to locate the various sensors.