OBJECTIVES Discuss the need for electronic stability control (ESC). List the sensors needed for the ESC system. Describe how a traction control (TC) system works. List the steps in the diagnostic process for ESC and TC system faults.

THE NEED FOR ELECTRONIC STABILITY CONTROL Purpose and Function Electronic stability control (ESC) is system designed to help drivers keep control of their cars Helps prevent run-off-road crashes and rollovers

THE NEED FOR ELECTRONIC STABILITY CONTROL System Requirements ESC has the following features: Applies individual brakes to maintain directional stability. Uses sensors to determine if vehicle is not under control. Uses steering wheel position sensor to determine intended direction.

THE NEED FOR ELECTRONIC STABILITY CONTROL System Requirements ESC has the following features: Operates at all vehicle speeds except low speeds.

THE NEED FOR ELECTRONIC STABILITY CONTROL System Requirements ESC applies individual brakes if either of these conditions occur: Oversteering: rear of vehicle moves outward or breaks loose Can result in loss of control

THE NEED FOR ELECTRONIC STABILITY CONTROL System Requirements ESC applies individual brakes if either of these conditions occur: Understeering: front of vehicle continues straight when turning

FIGURE 19.1 The electronic stability control (ESC) system applies individual wheel brakes to keep the vehicle under control of the driver.

THE NEED FOR ELECTRONIC STABILITY CONTROL System Requirements ESC lamp—called telltale lamp—remains on as long as malfunction exists when ignition is on Telltale lamp flashes to indicate when ESC system is operating

THE NEED FOR ELECTRONIC STABILITY CONTROL System Requirements Some manufacturers install switch to temporarily disable ESC Feature useful on certain occasions When a vehicle is stuck in sand or gravel

THE NEED FOR ELECTRONIC STABILITY CONTROL System Requirements Feature useful on certain occasions When vehicle is being operated on racetrack

THE NEED FOR ELECTRONIC STABILITY CONTROL System Requirements ESC automatically turns back on when ignition is turned off and then on again

FIGURE 19.2 The sine with dwell test is designed to test the electronic stability control (ESC) system to determine if the system can keep the vehicle under control.

FIGURE 19.3 Using a simulator is the most cost-effective way for vehicle and aftermarket suspension manufacturers to check that the vehicle is able to perform within the FMVSS No. 126 standard for vehicle stability.

ESC SENSORS Steering Wheel Position Sensor May also be called a hand-wheel position sensor Provides computer with signals related to steering wheel position, speed, and direction

FIGURE 19.4 The hand-wheel position sensor is usually located at the base of the steering column.

FIGURE 19.5 Hand-wheel (steering wheel) position sensor schematic.

ESC SENSORS Vehicle Speed Sensor Used by Electronic Brake Control Module to help control suspension system Vehicle speed (VS) sensor is magnetic sensor VS sensor generates analog signal whose frequency increases as speed increases

FIGURE 19.6 The VS sensor information is transmitted to the EBCM by Class 2 serial data.

ESC SENSORS Lateral Acceleration Sensor Provides suspension control module with feedback regarding cornering forces This type of sensor called G-sensor

ESC SENSORS Lateral Acceleration Sensor Letter “G” stands for gravity Information processed by suspension control module

ESC SENSORS Lateral Acceleration Sensor Module provides appropriate damping on inboard and outboard dampers during cornering events This sensor can be stand-alone unit or combined with yaw rate sensor

ESC SENSORS Lateral Acceleration Sensor Typically mounted in passenger compartment: Under front seat In center console On package shelf

FIGURE 19.8 A lateral acceleration sensor is usually located under the center console and can be easily checked by unbolting it and turning it on its side while monitoring the sensor value using a scan tool.

FIGURE 19.7 A schematic showing the lateral acceleration sensor and EBCM.

ESC SENSORS Yaw Rate Sensor Provides information to suspension control module and EBCM Information used to determine how far vehicle has deviated from intended direction

ESC SENSORS Yaw Rate Sensor Can be stand-alone unit or combined with lateral acceleration sensor Typically mounted under front seat, in center console, or on rear package shelf Sensor sets DTC codes

FIGURE 19.9 Yaw rate sensor showing the typical location and schematic.

TRACTION CONTROL Traction Control Operation Outputs of TC system can include one or more of the following: Retard ignition timing to reduce engine torque Decrease fuel injector pulse-width to reduce fuel delivery to reduce engine torque

TRACTION CONTROL Traction Control Operation Reduce amount of intake air if engine is equipped with an electronic throttle control (ETC) Reducing intake air will reduce engine torque Upshift the automatic transmission/transaxle Shifting into higher gear reduces torque Traction Control Operation Most TC systems can reduce positive wheel slip at all speeds

FIGURE 19.10 Typical traction control system that uses wheel speed sensor information and the engine controller (PCM) to apply the brakes at lower speeds and also reduce engine power applied to the drive wheels.

FIGURE 19.11 Wheel speed sensor information is used to monitor if a drive wheel is starting to spin.

FIGURE 19.12 A traction control or low traction light on the dash is confusing to many drivers.

ESC/TC DIAGNOSIS ESC and TC systems use some of same sensors and controllers Diagnosis is about the same for both Follow recommended procedures in service information

ESC/TC DIAGNOSIS Usual procedure follows these steps: STEP 1: Verify customer concern. STEP 2: Perform thorough visual inspection. STEP 3: Check service information for specified procedure to retrieve DTCs. Check related technical service bulletins Most vehicles require factory-brand scan tool

ESC/TC DIAGNOSIS STEP 4: Following troubleshooting procedure specified to fix root cause of problem. STEP 5: Repair the fault. STEP 6: Road test the vehicle under same conditions that caused the fault.

FIGURE 19.13 The use of a factory scan tool is often needed to diagnose the ESC system.

SUMMARY ESC and TC systems use some of same sensors and controllers ESC lamp—called telltale lamp—remains on as long as malfunction exists when ignition is on VS sensor generates analog signal whose frequency increases as speed increases Most TC systems can reduce positive wheel slip at all speeds ESC and TC systems use some of same sensors and controllers