Excessive thrust angle can cause the vehicle to go down the road at an angle with the steering wheel turned to one side. It compares the direction that the rear axle is aimed with the centerline of the vehicle. The thrust angle is an imaginary line drawn perpendicular to the rear axle’s centerline. The other possibility is the extra 50º on an off ramp may trigger the ESC system because it is interpreting the signals as an understeer condition.Īnother false activation scenario can be caused by an excessive thrust angle. The ESC might perform a correction by activating the brakes in order to get the steering angle to match what the other sensors are seeing. Let’s say a steering position sensor is giving a false reading of an extra 50º when the car is traveling in a straight line. All this time the sensors are monitoring what the driver is doing and the effectiveness of the correction. The next action might be to increase braking force on the inside front and/or outside rear tire to try to get the vehicle to rotate. The first action might be to close the throttle to transfer weight to the front so the tires can gain traction. The ESC system intervenes to try to make the vehicle turn. The ESC computer also sees that the driver’s steering angle is greater than the actual path measured by the yaw and lateral accelerometers. The ESC computer sees the understeer event via the sensors long before the driver realizes it. The driver will continue to increase the steering angle, but the lack of traction keeps the vehicle going straight. Let’s examine what happens during an understeer condition where the wheel turns, but the vehicle continues to travel in a straight line. The other sensors tell the ESC system what the vehicle is actually doing. This input tells the ESC system what the driver wants to do. The most important sensor is the steering angle sensor (SAS), which measures steering angle, steering wheel speed and torque applied by the driver. If these sensors come unbolted from their mountings, they need to be calibrated. These sensors are typically found in a module or “sensor cluster” under the center console as near as possible to the vehicle’s center of gravity. A yaw sensor measures the vehicle’s rotation on its vertical axis. Most vehicles have two accelerometer sensors that measure the gravitational force (g-force) generated by cornering and braking - one measures braking and acceleration, the other measures cornering forces. Solving these problems requires thinking like an ESC system. Some customers may complain the ESC activates on slower corners or on highway off ramps. In these cases, you may notice that one wheel is covered in brake dust. The customer may not notice an issue until there is a mechanical problem with the brakes. The source of the problem can be more than one sensor and can even be traced to alignment angles. The next false-activation scenario involves the ESC system. Instead of activating the ABS module and causing long stops, the system will deactivate and the ABS warning light will turn on. These new systems are also able to detect when each tooth passes by the sensor, instead of relying on the voltage generated to determine wheel speed.įalse activations are still a problem with active systems, but more advanced modules are able to determine if a wheel is locked or if there is a wheel speed sensor problem. New magnetoresistive sensors or “active” wheel speed sensors are not prone to issues of metal accumulation on the tip of the sensor. On these older systems with passive sensors, the cure for false activation is to clean the tip of the wheel speed sensor, inspect the tone ring and adjust the air gap. The driver might experience a longer than normal stop. A weak signal from a sensor is interpreted as a locked wheel, which triggers the computer to activate the ABS system and release brake pressure in an attempt to unlock the wheel. This problem usually starts with the wheel speed sensors. The most common complaint on older vehicles is ABS activation at speeds between 3-15 mph. Some may also experience a drop in power or the vehicle may suddenly pull in one direction. The customer may feel feedback in the brake pedal like a pulsation or sudden drop. False activation incidents involve the ABS modulator taking over braking or intervening to restore vehicle stability.
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