1. CHAPTER 10 Electronic Stability Control Systems

2. Discuss how an electronic stability system works.
OBJECTIVES
After studying Chapter 10, the reader will be able to:
Prepare for Brakes (A5) ASE certification test content area “F” (Antilock Brake System Diagnosis and Repair).
Discuss how an electronic stability system works.
List the sensors needed for the ESC system.
Explain how the ESC system helps keep the vehicle under control.
Describe how a traction control system works.
List the steps in the diagnostic process for ESC and TC system faults.

3. KEY TERMS Electronic brake control module (EBCM) ESC
Hand-wheel position sensor
Lateral acceleration sensor
Oversteer
Positive slip
Sine with dwell (SWD) test
Steering wheel position sensor
Telltale light
Traction control (TC)
Understeer
Vehicle speed (VS) sensor
Yaw rate sensor

4. THE NEED FOR ELECTRONIC STABILITY CONTROL PURPOSE AND FUNCTION
Electronic stability control (ESC) is a system designed to help drivers to maintain control of their vehicles in situations where the vehicle is beginning to lose control.
Keeping the vehicle on the road prevents run-off-road crashes, which are the conditions that lead to most singlevehicle accidents and rollovers.

5. THE NEED FOR ELECTRONIC STABILITY CONTROL SYSTEM REQUIREMENTS
The ESC is defined as a system that has all of the following features:
1. Helps vehicle directional stability by applying and adjusting individual wheel brakes to help bring the vehicle back to the intended direction.
2. Uses sensors to determine when the vehicle is not under control.
3. Uses a steering wheel position sensor to determine the intended direction of the driver.
4. Operates at all vehicle speeds, except at low speeds where loss of control is unlikely.

6. THE NEED FOR ELECTRONIC STABILITY CONTROL SYSTEM REQUIREMENTS
FIGURE 10–1 The electronic stability control (ESC) system applies individual wheel brakes to keep the vehicle under control of the driver.

7. THE NEED FOR ELECTRONIC STABILITY CONTROL SYSTEM REQUIREMENTS
TELLTALE LAMP
ESC SWITCH

8. FEDERAL MOTOR VEHICLE SAFETY STANDARD (FMVSS) NO. 126
Federal Motor Vehicle Safety Standard (FMVSS) No. 126 (June 26, 2008), Electronic Stability Control Systems, requires that all passenger cars, multipurpose passenger vehicles, trucks, and buses that have a gross vehicle weight rating (GVWR) of 10,000 pounds ( 4,536 kg) or less to be equipped with an electronic stability control (ESC) system by September 1, 2011 (2012 model year vehicles).

9. FEDERAL MOTOR VEHICLE SAFETY STANDARD (FMVSS) NO. 126
The ESC system must meet the following requirements:
1. The ESC system must be able to apply all four brakes individually. This means that the vehicle must be equipped with a four-channel antilock braking system (ABS) which uses a wheel speed sensor at each wheel.
2. The ESC must be programmed to work during all phases of driving including acceleration, coasting, and deceleration (including braking).
3. The ESC system must work when the antilock brake system (ABS) or Traction Control is activated.

10. SINE WITH DWELL TEST
The standardized test used to determine if an electronic stability control system functions okay is called the sine with dwell (SWD) test.
A vehicle is driven at 50 mph (80 km/h) and driven on a curved course that looks like a sine wave or the letter “S” on its side.
Then the vehicle is held in a straight-ahead position for 0.5 second (500 milliseconds) and before being steered back onto the curved section of the test.

11. SINE WITH DWELL TEST
FIGURE 10–2 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.

12. Can a Vehicle with a Modified Suspension Pass the Test?
Yes, if the system is properly engineered. To be sure, check with the company offering a suspension test to verify that the vehicle will still be able to pass the sine with dwell (SWD) test. This ensures that any changes are within the range where the ESC system can control the vehicle during emergency maneuvers.

13. Can a Vehicle with a Modified Suspension Pass the Test?
FIGURE 10–3 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.

14. ESC SENSORS
STEERING WHEEL POSITION SENSOR
VEHICLE SPEED SENSOR
LATERAL ACCELERATION SENSOR
YAW RATE SENSOR

15. ESC SENSORS
FIGURE 10–4 The hand-wheel position sensor is located at the base of the steering column.

16. ESC SENSORS
FIGURE 10–5 Hand-wheel (steering wheel) position sensor schematic.

17. ESC SENSORS
FIGURE 10–6 The VS sensor information is transmitted to the EBCM by Class 2 serial data.

18. ESC SENSORS
FIGURE 10–7 A schematic showing the lateral acceleration sensor and EBCM.

19. A Visual Inspection is Often the Key to Success.
An ABS amber warning light and a stored U0124 code (lost communications with lateral acceleration sensor) lead to looking at service information for the location of the sensor.
It was found to be located under the center console.
A visual check of the area showed that a sticky soft drink had likely spilled from the cup holder.
The liquid had gotten into the electrical connector and caused the fault.

20. A Visual Inspection is Often the Key to Success.
FIGURE 10–8 The lateral accelerometer sensor (G-sensor) is usually located under the center console.

21. ESC SENSORS
FIGURE 10–9 Yaw rate sensor showing the typical location and schematic.

22. TRACTION CONTROL PURPOSE AND FUNCTION
Traction control (TC) can be separate or used as part of the electronic stability control (ESC) system.
Traction control allows an ABS system to control wheel spin during acceleration.
When tires lose traction during acceleration, it is called positive slip.
FIGURE 10–10 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.

23. TRACTION CONTROL SYSTEM COMPONENTS
The main controller for the traction can include one of the following, depending on make, model, and year of vehicle:
1. The body control module (BCM)
2. The Power Train Control Module (PCM)
3. The antilock brake system controller

24. TRACTION CONTROL SYSTEM COMPONENTS
The controller uses inputs from several sensors to determine if a loss of traction is occurring.
The input signals used for traction control include:
Throttle position (TP) sensor
Wheel speed sensor (WSS)
Engine speed (RPM)
Transmission range switch

25. TRACTION CONTROL TRACTION CONTROL OPERATION
The outputs of the traction control system can include one or more of the following:
Retard ignition timing to reduce engine torque.
Decrease the fuel injector pulse-width to reduce fuel delivery to the cylinder to reduce engine torque.
Reduce the amount of intake air if the engine is equipped with an electronic throttle control (ETC). Reduced airflow will reduce engine torque.
Upshift the automatic transmission/transaxle. If the transmission is shifted into a higher gear, the torque applied to the drive wheels is reduced.

26. TRACTION CONTROL TRACTION CONTROL OPERATION
FIGURE 10–11 Wheel speed sensor information is used to monitor if a drive wheel is starting to spin.

27. TRACTION CONTROL TRACTION CONTROL OPERATION
FIGURE 10–12 A traction control or low traction light on the dash is confusing to many drivers. When the lamp is on or flashing, it indicates that a low traction condition has been determined and the traction control system is working to restore traction. A flashing traction dash light does not indicate a fault.

28. TRACTION CONTROL TRACTION ACTIVE LAMP
On most applications, a “TRAC CNTL” indicator light or “TRACTION CONTROL ACTIVE” message flashes on the instrumentation when the system is engaging traction control.
This helps alert the driver that the wheels are losing traction.
In most applications, the message does not mean there is anything wrong with the system—unless the ABS warning lamp also comes on, or the traction control light remains on continuously.

29. TRACTION CONTROL TRACTION DEACTIVATION SWITCH
Many vehicles with traction control have a dash-mounted switch that allows the driver to deactivate the system when desired (as when driving in deep snow).
An indicator light shows when the system is on or off, and may also signal the driver when the traction control system is actively engaged during acceleration.

30. Does Traction Control Engage Additional Drive Wheels?
When the term traction control is used, many people think of four-wheel-drive or all-wheel-drive vehicles and power trains. Instead of sending engine torque to other drive wheels, it is the purpose and function of the traction control system to prevent the drive wheel(s) from slipping during acceleration. A slipping tire has less traction than a nonslipping tire—therefore, if the tire can be kept from slipping (spinning), more traction will be available to propel the vehicle. Traction control works with the engine computer to reduce torque delivery from the engine, as well as the controller to apply the brakes to the spinning wheel if necessary to regain traction.

31. ESC/TC DIAGNOSIS
Because the electronic stability control (ESC) and traction control (TC) systems use some of the same sensors and controllers, the diagnosis for them is about the same.
To diagnose faults with either system, follow the recommended procedures found in service information.
The usual procedure involves the following steps.
STEP 1 Verify the customer concern (complaint)
STEP 2 Perform a thorough visual inspection
STEP 3 Check service information
STEP 4 Follow the troubleshooting procedure
STEP 5 Repair the fault.
STEP 6 Road test the vehicle

32. ESC/TC DIAGNOSIS
FIGURE 10–13 The use of a factory scan tool is often needed to diagnose the ESC system.

33. SUMMARY
The purpose and function of the electronic stability control (ESC) system is to help maintain directional stability under all driving conditions by applying individual wheel brakes as needed to restore control.
The Federal Motor Vehicle Safety Standard (FMVSS) number 126 requires that all vehicles with a gross vehicle weight of less than 10,000 pounds be equipped with ESC by September 1, 2011.
The ESC can be switched off but will default to on when the ignition is turned back on.
The sine with dwell test (SWD) is the standard test used to test electronic stability control systems.

34. SUMMARY
Electronic stability control sensors include steering wheel position sensor, vehicle speed sensor, lateral acceleration sensor, and yaw rate sensor.
Traction control (TC) systems use a variety of actions to help achieve traction of the drive wheels during acceleration, including retarding ignition timing, upshifting the transmission, and applying individual wheel brakes.
Diagnosis of the ESC or TC system involves the following steps:
a. Verify the customer concern.
b. Perform a thorough visual inspection.
c. Check service information for specified test procedures.
d. Follow specified testing procedures.
e. Repair the fault.
f. Perform a roadtest to verify the repair.

35. REVIEW QUESTIONS
What is the difference between oversteering and understeering?
What is the “sine with dwell” test?
What are some of the other names used to identify an electronic stability control (ESC) system?
What sensors are used in the electronic stability control system?
What action does the traction control system perform to help the drive wheels maintain traction during acceleration?
What is the typical diagnostic procedure to follow when troubleshooting a fault with the electronic stability control or traction control system?

36. CHAPTER QUIZ
1. The electronic stability control (ESC) system requires that the vehicle be equipped with what type of brake system?
Four-wheel disc brakes
Four-channel ABS
Three-channel ABS
Front disc with rear drum brakes

37. CHAPTER QUIZ
2. Which Federal Motor Safety Standard requires electronic stability control to be on all vehicles by 2011?
126
113
109
101

38. CHAPTER QUIZ
3. What is the name of the standard test that is performed to verify ESC operation?
ESC plus
Vehicle stability enhancement test
Sine with dwell
Anti-skid test

39. CHAPTER QUIZ
4. What other name is used to describe an electronic stability control (ESC) system?
Vehicle Stability Assist (VSA)
Electronic Stability Program (ESP)
Vehicle Dynamic Control (VDC)
Any of the above

40. CHAPTER QUIZ
5. Which sensor is used by the ESC controller to determine the driver’s intended direction?
Yaw sensor
Steering wheel (hand-wheel) position sensor
Vehicle speed (VS) sensor
Lateral acceleration sensor

41. CHAPTER QUIZ
6. A driver notices that the “Low Traction” warning light flashes at times during heavy acceleration. What is the most likely cause?
Normal operation
Fault with a wheel speed sensor
A defective vehicle speed (VS) sensor
A fault with the ABS controller

42. CHAPTER QUIZ
7. A lateral acceleration sensor is usually located where in the vehicle?
Under the front seat
In the center console
On the package shelf
Any of the above locations

43. CHAPTER QUIZ
8. If a vehicle tends to continue straight ahead while cornering, this condition is called ________.
Understeer
Plowing
Tight
All of the above

44. CHAPTER QUIZ
9. Traction control uses the antilock braking system and other devices to limit ________ of the drive wheels during acceleration.
Positive slip
Negative slip

45. 10. A traction control system can often control all except ________.
CHAPTER QUIZ
10. A traction control system can often control all except ________.
Limit engine torque delivered to the drive wheel
Engage four-wheel drive
Upshift the automatic transmission
Apply the wheel brake to the wheel that is losing traction