ESP / ESC (electronic stability control)
Definition
ESP builds on the ABS hydraulic unit and adds a yaw rate and lateral acceleration sensor, a steering angle sensor and brake pressure sensors so that the module can compare where the driver is steering with where the car is actually going. If it detects understeer or oversteer it brakes individual wheels and asks the ECU to reduce torque to bring the car back on line; it also provides traction control, brake assist, trailer sway control and hill start assist. Faults are a steering angle sensor that has lost its zero point after battery disconnection, wheel alignment or steering repairs, a yaw sensor with a drifted offset or loose mounting, brake pressure sensor faults, a brake light switch that is out of adjustment, and all of the ABS wheel speed sensor problems. Symptoms are an ESP lamp (often with ABS), the system intervening when driving straight, or ESP unavailable messages; after many repairs the steering angle sensor and yaw sensor must be recalibrated with a scan tool. Codes: C0040-series (wheel speeds), C0051 (steering angle sensor), C0196 (yaw rate sensor), C0186 (lateral acceleration sensor), C0131 (pressure sensor), C0161 (brake switch), U0126 (lost communication with steering angle sensor module), U0122 (vehicle dynamics module), VAG 00778/01435.