1. CHAPTER 9 Electronic Suspension Systems

2. Describe how suspension height sensors function.
OBJECTIVES
After studying Chapter 9, the reader will be able to:
Prepare for ASE Suspension and Steering (A4) certification test content area “B” (Suspension System Diagnosis and Repair).
Describe how suspension height sensors function.
Explain the use of the various sensors used for electronic suspension control.
Discuss the steering wheel position sensor.
Explain how solenoids and actuators are used to control the suspension.

3. KEY TERMS Actuator Air suspension Armature AS
Automatic level control (ALC)
CCVRTMR
Computer command ride (CCR)
Desiccant
Driver selector switch
EBCM
ECU
Electromagnet
Handwheel position sensor
Height sensor
Input
Lateral accelerometer sensor
LED
Magneto-rheological (MR)
Mode select switch
Motor
MRRTD
Output
Perform ride mode
Photocell
Phototransistor
Pulse width
Pulse-width modulation
Real-time dampening (RTD)
RPO
RSS
Selectable ride (SR)
Solenoid
Solenoid controlled damper
Stabilitrak
Steering wheel position sensor
Touring ride mode
Vehicle stability enhancement system (VSES)
VS sensor
Yaw rate sensor

4. THE NEED FOR ELECTRONIC SUSPENSIONS
Since the mid-1980s, many vehicle manufacturers have been introducing models with electronic suspension controls that provide a variable shock stiffness or spring rate.
The main advantage of electronic controls is that the suspension can react to different conditions.
The system provides a firm suspension feel for fast cornering and quick acceleration and braking, with a soft ride for cruising.

5. THE NEED FOR ELECTRONIC SUSPENSIONS
FIGURE 9–1 An electronically controlled suspension system can help reduce body roll and other reactions better than most conventional suspension systems.

6. ELECTRONIC SUSPENSION CONTROLS AND SENSORS
Sensors and switches provide input to the electronic control module (ECM), or system computer.
The ECM, which may also be referred to as the electronic control unit (ECU), is a small computer that receives input in the form of electrical signals from the sensors and switches and provides output electrical signals to the system actuators.

7. ELECTRONIC SUSPENSION CONTROLS AND SENSORS
FIGURE 9–2 Input devices monitor conditions and provide information to the electronic control module, which processes the information and operates the actuators to control the movement of the suspension.

8. ELECTRONIC SUSPENSION CONTROLS AND SENSORS HEIGHT SENSORS
Sensors, which are the input devices that transmit signals to the ECM, monitor operating conditions and component functions.
A height sensor senses the vertical relationship between the suspension component and the body.
Its signal indicates to the ECM how high the frame or body is, or how compressed the suspension is.
A number of sensor designs are used to determine ride height, including a photocell type of sensor.

9. ELECTRONIC SUSPENSION CONTROLS AND SENSORS HEIGHT SENSORS
FIGURE 9–3 A typical electronic suspension height sensor, which bolts to the body and connects to the lower control arm through a control link and lever.

10. ELECTRONIC SUSPENSION CONTROLS AND SENSORS HEIGHT SENSORS
FIGURE 9–4 When suspension action moves the lever, it rotates the slotted disc and varies how much of the photo transistor is exposed to the LEDs, which vary the input signal.

11. ELECTRONIC SUSPENSION CONTROLS AND SENSORS GENERAL MOTORS ELECTRONIC SUSPENSION SENSORS
There are five different sensors found on electronic suspension systems, and GM vehicles can have between one and four of these sensors, depending on the system.
Depending on the vehicle, the suspension position sensor may be called by a different name. It can be called:
An automatic level control sensor
An electronic suspension position sensor
A position sensor
An air suspension sensor

12. ELECTRONIC SUSPENSION CONTROLS AND SENSORS GENERAL MOTORS ELECTRONIC SUSPENSION SENSORS
FIGURE 9–5 Typical suspension position sensor.

13. ELECTRONIC SUSPENSION CONTROLS AND SENSORS GENERAL MOTORS ELECTRONIC SUSPENSION SENSORS
FIGURE 9–6 A three-wire suspension position sensor schematic.

14. ELECTRONIC SUSPENSION CONTROLS AND SENSORS GENERAL MOTORS ELECTRONIC SUSPENSION SENSORS
FIGURE 9–7 A suspension height sensor.

15. ELECTRONIC SUSPENSION CONTROLS AND SENSORS STEERING WHEEL POSITION SENSOR
Depending on the vehicle, the steering wheel position sensor may also be called a handwheel position sensor.
The function of this sensor is to provide the control module with signals relating to steering wheel position, the speed and direction of handwheel position.
The sensor is found on most real-time dampening (RTD) and road-sensing suspension (RSS) applications.

16. ELECTRONIC SUSPENSION CONTROLS AND SENSORS STEERING WHEEL POSITION SENSOR
FIGURE 9–8 The steering wheel position (handwheel position) sensor wiring schematic and how the signal varies with the direction that the steering wheel is turned.

17. ELECTRONIC SUSPENSION CONTROLS AND SENSORS STEERING WHEEL POSITION SENSOR
FIGURE 9–9 The handwheel position sensor is located at the base of the steering column.

18. ELECTRONIC SUSPENSION CONTROLS AND SENSORS STEERING WHEEL POSITION SENSOR
FIGURE 9–10 Steering wheel (handwheel) position sensor schematic.

19. ELECTRONIC SUSPENSION CONTROLS AND SENSORS VEHICLE SPEED SENSOR
The vehicle speed (VS) sensor is used by the EBCM to help control the suspension system.
The vehicle speed sensor is a magnetic sensor and generates an analog signal whose frequency increases as the speed increases.
The ride is made firmer at high speeds and during braking and acceleration and less firm at cruise speeds.
FIGURE 9–11 The VS sensor information is transmitted to the EBCM by Class 2 serial data.

20. ELECTRONIC SUSPENSION CONTROLS AND SENSORS PRESSURE SENSOR
A pressure transducer (sensor) is typically mounted on the compressor assembly.
This sensor is typically found on suspension systems that use a compressor assembly.
The main function of the pressure sensor is to provide feedback to the suspension control module about the operation of the compressor.
The sensor assures both that a minimum air pressure is maintained in the system and that a maximum value is not exceeded.

21. ELECTRONIC SUSPENSION CONTROLS AND SENSORS PRESSURE SENSOR
FIGURE 9–12 An air pressure sensor.

22. ELECTRONIC SUSPENSION CONTROLS AND SENSORS LATERAL ACCELEROMETER SENSOR
The function of the lateral accelerometer sensor is to provide the suspension control module with feedback regarding vehicle cornering forces.
This type of sensor is also called a G-sensor, with the letter “G” representing the force of gravity.
For example, when a vehicle enters a turn, the sensor provides information as to how hard the vehicle is cornering.
This information is processed by the suspension control module to provide appropriate damping on the inboard and outboard dampers during cornering events.
The lateral accelerometer sensor is found on the more complex suspensions systems, such as RTD and RSS systems that incorporate the vehicle stability enhancement system (VSES).

23. ELECTRONIC SUSPENSION CONTROLS AND SENSORS LATERAL ACCELEROMETER SENSOR
FIGURE 9–13 A schematic showing the lateral acceleration sensor and the EBCM.

24. Quick and Easy “G” Sensor Test
Most factory scan tools will display the value of sensors, including the lateral accelerometer sensor (G-sensor). However, the G-sensor value will read zero unless the vehicle is cornering. A quick and easy test of the sensor is to simply unbolt the sensor and rotate it 90 degrees with the key on engine off. Now the sensor is measuring the force of gravity and should display 1.0 G on the scan tool. If the sensor does not read close to 1.0 G or reads zero all of the time, the sensor or the wiring is defective.

25. Quick and Easy “G” Sensor Test
FIGURE 9–14 The lateral accelerometer sensor (G-sensor) is usually located under the center console.

26. ELECTRONIC SUSPENSION CONTROLS AND SENSORS YAW RATE SENSOR
The yaw rate sensor provides information to the suspension control module and the EBCM.
This information is used to determine how far the vehicle has deviated from the driver’s intended direction.
The yaw sensor is used on vehicles equipped with Electronic Stability Control (ESC).

27. ELECTRONIC SUSPENSION CONTROLS AND SENSORS YAW RATE SENSOR
FIGURE 9–15 Yaw rate sensor showing the typical location and schematic.

28. ELECTRONIC SUSPENSION CONTROLS AND SENSORS DRIVER SELECTOR SWITCH
The driver selector switch is a two- or three-mode switch, usually located in the center console, and is an input to the suspension control module.
The switch that is used to select either touring (soft) or performance (firm) ride is found on the Selectable Ride (SR) and the Computer Command Ride (CCR) systems.
The mode select switch status is generally displayed on a scan tool.
The three-position switch is used on the Corvette RTD system, and allows the driver to select three modes of operation:
Tour
Sport
Performance

29. ELECTRONIC SUSPENSION SYSTEM ACTUATORS
Each actuator in an electronically controlled suspension system receives output signals from the ECM and responds to these signals, or commands, by performing a mechanical action.
Actuators are usually inductive devices that operate using an electromagnetic field.
A simple electromagnet consists of a soft iron core with a coil of wire, usually copper, wrapped around it.

30. ELECTRONIC SUSPENSION SYSTEM ACTUATORS
FIGURE 9–16 A magnetic field is created whenever an electrical current flows through a coil of wire wrapped around an iron core.

31. ELECTRONIC SUSPENSION SYSTEM ACTUATORS
FIGURE 9–17 When magnets are near each other, like poles repel and opposite poles attract.

32. ELECTRONIC SUSPENSION SYSTEM ACTUATORS SOLENOIDS
In a solenoid, the core of the electromagnet also acts as a plunger to open and close a passage or to move a linkage.
Solenoids are cylindrically shaped with a metal plate at one end and open at the other end to allow the plunger to move in and out.
The electromagnetic coils are placed along the sides of the cylinder.
A preload spring forces the plunger toward one end of the device when the solenoid is de-energized, or there is no current in the coil.

33. ELECTRONIC SUSPENSION SYSTEM ACTUATORS SOLENOIDS
FIGURE 9–18 When electrical current magnetizes the plunger in a solenoid, the magnetic field moves the plunger against spring force. With no current, the spring pushes the plunger back to its original position.

34. ELECTRONIC SUSPENSION SYSTEM ACTUATORS SOLENOIDS
FIGURE 9–19 This air supply solenoid blocks pressurized air from the air spring valves when off. The plunger pulls upward to allow airflow to the air spring valves when the solenoid is energized.

35. ELECTRONIC SUSPENSION SYSTEM ACTUATORS ACTUATOR MOTORS
If a current-carrying conductor is placed in a magnetic field, it tends to move from the stronger field area to the weaker field area.
A motor uses this principle to convert electrical energy into mechanical movement.
Electrical current is directed through the field coils on the motor frame to create a magnetic field within the frame.
By applying an electrical current to the armature, which is inside the motor frame, the armature rotates from a strong field area to a weaker field area.

36. ELECTRONIC SUSPENSION SYSTEM ACTUATORS ACTUATOR MOTORS
FIGURE 9–20 An actuator motor uses a permanent magnet and four stator coils to drive the air spring control rod.

37. ELECTRONIC SUSPENSION SYSTEM ACTUATORS ACTUATOR MOTORS
FIGURE 9–21 The stator coils of the actuator are energized in three ways to provide soft, medium, or firm ride from the air springs and shock absorbers.

38. TYPES OF ELECTRONIC SUSPENSION
The types of electronic suspension systems used on General Motors vehicles, as examples, include:
Selectable Ride
Automatic Level Control
Air Suspension
Computer Command Ride
Real-Time Dampening/Road-Sensing Suspension
Vehicle Stability Enhancement System
Magneto-Rheological Suspension (F55)

39. TYPES OF ELECTRONIC SUSPENSION
FIGURE 9–22 Selectable Ride as used on Chevrolet and GMC pickup trucks.

40. TYPES OF ELECTRONIC SUSPENSION
FIGURE 9–23 ALC maintains the same ride height either loaded or unloaded by increasing or decreasing the air pressure in the rear air shocks.

41. TYPES OF ELECTRONIC SUSPENSION
FIGURE 9–24 A typical schematic showing the air suspension compressor assembly and sensor.

42. TYPES OF ELECTRONIC SUSPENSION
FIGURE 9–25 The typical variable-rate air spring system uses three height sensors, two in the front and one in the rear, to monitor trim height and to provide input signals to the ECM.

43. TYPES OF ELECTRONIC SUSPENSION
FIGURE 9–26 The air spring compressor assembly is usually mounted on rubber cushions to help isolate it from the body of the vehicle. All of the air entering or leaving the air springs flows through the regenerative air dryer.

44. TYPES OF ELECTRONIC SUSPENSION
FIGURE 9–27 A solenoid valve at the top of each spring regulates airflow into and out of the air spring.

45. TYPES OF ELECTRONIC SUSPENSION
FIGURE 9–28 Schematic showing Computer Command Ride (CCR) system.

46. TYPES OF ELECTRONIC SUSPENSION
FIGURE 9–29 Schematic showing the shock control used in the RSS system.

47. TYPES OF ELECTRONIC SUSPENSION
FIGURE 9–30 Bi-state dampers (shocks) use a solenoid to control fluid flow in the unit to control compression and rebound actions.

48. Check the RPO Code
Whenever working on the suspension system check the RPO (regular production option) code for the type of suspension used. For example, the F55 RPO may be called by a different name depending on the make and model of vehicle. Also, service procedures will be different on the same vehicle depending on whether it is equipped with an F45 or an F55 system. The General Motors vehicle RPO codes are on a sticker on the spare tire cover in the trunk or in the glove compartment.

49. TYPES OF ELECTRONIC SUSPENSION
FIGURE 9–31 Solenoid valve controlled shock absorber circuit showing the left front (LF) shock as an example.

50. TYPES OF ELECTRONIC SUSPENSION
FIGURE 9–32 A typical CCR module schematic.

51. TYPES OF ELECTRONIC SUSPENSION
FIGURE 9–33 The three dampening modes of a CCR shock absorber.

52. TYPES OF ELECTRONIC SUSPENSION
FIGURE 9–34 Integral shock solenoid.

53. What Are Self-Leveling Shocks?
A German company, ZF Sachs, supplies a selfleveling shock absorber to several vehicle manufacturers, such as Chrysler for use on the rear of minivans, plus BMW, Saab, and Volvo. The self-leveling shocks are entirely self-contained and do not require the use of height sensors or an external air pump.
The shock looks like a conventional shock absorber but contains the following components:
Two reservoirs in the outer tube
An oil reservoir (low-pressure reservoir)
A high-pressure chamber

54. What Are Self-Leveling Shocks?
Inside the piston rod is the pump chamber containing an inlet and an outlet valve. When a load is placed in the rear of the vehicle, it compresses the suspension and the shock absorber. When the vehicle starts to move, the internal pump is activated by the movement of the body. Extension of the piston rod causes oil to be drawn through the inlet valve into the pump. When the shock compresses, the oil is forced through the outlet valve into the high-pressure chamber. The pressure in the oil reserve decreases as the pressure in the high-pressure chamber increases. The increasing pressure is applied to the piston rod, which raises the height of the vehicle.

55. What Are Self-Leveling Shocks?
When the vehicle’s normal height is reached, no oil is drawn into the chamber. Because the shock is mechanical, the vehicle needs to be moving before the pump starts to work. It requires about 2 miles of driving for the shock to reach the normal ride height. The vehicle also needs to be driven about 2 miles after a load has been removed from the vehicle for it to return to normal ride height.

56. What Are Self-Leveling Shocks?
FIGURE 9–35 A typical ZF Sachs self-leveling shock, as used on the rear of a Chrysler minivan.

57. AUTOMATIC LEVEL CONTROL (ALC)
Vehicles that have an air inflator system as part of the ALC system also have an air inflator switch.
The air inflator switch is an input to the ALC and AS system.
The inflator switch is used to control the air inflator system operation and provides a signal to the ALC or AS module to initiate compressor activation.
With the ignition on, the driver can turn the system to ON.
The switch will command the compressor to run for up to 10 minutes, allowing time to inflate a tire or other items requiring air.

58. AUTOMATIC LEVEL CONTROL (ALC)
INFLATOR OR COMPRESSOR RELAY
COMPRESSOR
AIR DRYER
EXHAUST SOLENOID

59. AUTOMATIC LEVEL CONTROL (ALC)
FIGURE 9–36 Schematic of the ALC system.

60. AUTOMATIC LEVEL CONTROL (ALC)
FIGURE 9–37 Air compressor assembly can be located at various locations depending on the vehicle.

61. AUTOMATIC LEVEL CONTROL (ALC)
FIGURE 9–38 The exhaust solenoid is controlled by the rear integration module (RIM).

62. AUTOMATIC LEVEL CONTROL (ALC)
FIGURE 9–39 Schematic showing the rear integration module (RIM) and how it controls the ALC compressor.

63. MAGNETO-RHEOLOGICAL (MR) SUSPENSION
MR fluid shocks use a working fluid inside the shock that can change viscosity rapidly depending on electric current sent to an electromagnetic coil in each device.
The fluid is called magneto-rheological (MR) and is used in monotube-type shock absorbers.
This type of shock and suspension system is called the magneto-rheological real-time damping (MRRTD) or chassis continuously variable real-time dampening magneto-rheological suspension (CCVRTMR).

64. MAGNETO-RHEOLOGICAL (MR) SUSPENSION
FIGURE 9–40 Vehicles that use magneto-rheological shock absorbers have a sensor located near each wheel, as shown on this C6 Corvette.

65. MAGNETO-RHEOLOGICAL (MR) SUSPENSION
FIGURE 9–41 The controller for the magneto-rheological suspension system on a C6 Corvette is located behind the right front wheel.

66. MAGNETO-RHEOLOGICAL (MR) SUSPENSION
FIGURE 9–42 A cutaway of a magneto-rheological shock absorber as displayed at the Corvette Museum in Bowling Green, Kentucky.

67. Can Computer-Controlled Shock Absorbers and Struts Be Replaced with Conventional Units?
Maybe. If the vehicle was manufactured with or without electronic or variable shock absorbers, it may be possible to replace the originals with the standard replacement units. The electrical connector must be disconnected, and this may cause the control system to store a diagnostic trouble code (DTC) and/or turn on a suspension fault warning light on the dash. Some service technicians have used a resistor equal in resistance value of the solenoid or motor across the terminals of the wiring connector to keep the controller from setting a DTC. All repairs to a suspension system should be done to restore the vehicle to like-new condition, so care should be exercised if replacing electronic shocks with nonelectronic versions.

68. TROUBLESHOOTING REAR ELECTRONIC LEVELING SYSTEMS
The first step with any troubleshooting procedure is to check for normal operation.
Some leveling systems require that the ignition key be on (run), while other systems operate all the time.
Begin troubleshooting by placing approximately 300 lb (135 kg) on the rear of the vehicle.
If the compressor does not operate, check to see if the sensor is connected to a rear suspension member and that the electrical connections are not corroded.

69. TROUBLESHOOTING REAR ELECTRONIC LEVELING SYSTEMS
FIGURE 9–43 Most electronic level-control sensors can be adjusted, such as this General Motors unit.

70. SUMMARY
General Motors uses seven types of electronic suspension under many different names.
Suspension height sensors and steering wheel (handwheel) position sensors are used in many systems.
A vehicle speed sensor signal is used to control the suspension at various speeds.
Many electronic suspension systems use a lateral accelerometer sensor, which signals the suspension computer when the vehicle is rapidly accelerating, braking, or cornering.
Solenoids and motors are used to control the suspension movement by moving valves in the shock absorbers or air springs.
An air pump and air shocks are used to raise the rear of the vehicle to compensate for a heavy load.

71. REVIEW QUESTIONS
What type of sensor is usually used on electronically controlled suspensions to sense the height of the vehicle?
Why is the vehicle speed sensor used as input for many electronic suspension systems?
What is a lateral accelerometer sensor and why is it used?
Why does the output side of the suspension air compressor contain a desiccant?

72. CHAPTER QUIZ
1. What type of sensor is used as a height sensor on vehicles equipped with an electronically controlled suspension?
Hall-effect
Photo cell
Potentiometer
All of the above

73. CHAPTER QUIZ
2. Which sensors do most vehicles use if equipped with electronic suspension?
Height sensors
Steering wheel position sensors
Lateral accelerometer sensors
All of the above

74. CHAPTER QUIZ
3. A lateral acceleration sensor is used to provide the suspension control module with feedback regarding ________ force.
Cornering
Acceleration
Braking
All of the above

75. CHAPTER QUIZ
4. A steering wheel position sensor is being discussed. Technician A says that the sensor is used to determine the direction the steering wheel is turned. Technician B says that the sensor detects how fast the steering wheel is turned. Which technician is correct?
Technician A only
Technician B only
Both Technicians A and B
Neither Technician A nor B

76. CHAPTER QUIZ
5. Technician A says that an electronic control module used in the suspension system is the same as that used for engine control. Technician B says that most electronically controlled suspension systems use a separate electronic control module. Which technician is correct?
Technician A only
Technician B only
Both Technicians A and B
Neither Technician A nor B

77. CHAPTER QUIZ
6. What type of actuator is used on electronically controlled suspensions?
Solenoid
Electric motor
Either a or b
Neither a nor b

78. CHAPTER QUIZ
7. Why is the typical rear load-leveling system connected to the ignition circuit?
To keep the system active for a given time after the ignition is switched off
To prevent the system from working unless the ignition key is on
To keep the compressor from running for an extended period of time
All of the above

79. CHAPTER QUIZ
8. Which sensor can be tested by unbolting the sensor and with the ignition on, engine off (KOEO), looking at the scan tool data?
“G” sensor
Wheel speed sensor
Vehicle speed sensor
Suspension sensor

80. CHAPTER QUIZ
9. The firm setting is usually selected by the electronic suspension control module whenever which of the following occurs?
High speed
Rapid braking
Rapid acceleration
All of the above

81. CHAPTER QUIZ
10. Which of the following is the least likely sensor to cause an electronic suspension fault?
Yaw sensor
Throttle position (TP) sensor
Steering wheel position sensor
Vehicle speed sensor