2. 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.

3. 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

4. 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.

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

6. 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

7. 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

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

9. 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

10. 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

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

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

13. 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.

14. 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.

15. 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

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

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

18. 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

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

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

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

22. 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

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

24. 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.

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

26. 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

27. 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

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

29. 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

30. 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

31. FIGURE 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.

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

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

34. 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

35. 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

36. 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.

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

38. 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