Halderman ch108 lecture

Automotive Technology, Fourth EditionJames Halderman

ELECTRONIC STABILITY CONTROL SYSTEMS

108 ELECTRONIC STABILITY CONTROL SYSTEMS

ObjectivesObjectives• The student should 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.

ObjectivesObjectives• The student should be able to:

– 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.

THE NEED FOR THE NEED FOR ELECTRONICELECTRONIC

STABILITY CONTROLSTABILITY CONTROL

The Need for Electronic Stability The Need for Electronic Stability ControlControl

• 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

• System Requirements– ESC has the following features:

1. Applies individual brakes to maintain directional stability.

2. Uses sensors to determine if vehicle is not under control.

3. Uses steering wheel position sensor to determine intended direction.

4. Operates at all vehicle speeds except low speeds.

• 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

• System Requirements– ESC applies individual brakes if either of

these conditions occur:• Understeering: front of vehicle continues

straight when turning

Figure 108-1 The electronic stability control (ESC) system applies individual wheel brakes to keep the vehicle under control of the driver.

• System Requirements– NOTE: When the brakes are applied during

these corrections, a thumping sound and vibration may be sensed.

• 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

• System Requirements– Some manufacturers install switch to

temporarily disable ESC– Feature useful on certain occasions

• When a vehicle is stuck in sand or gravel

• System Requirements– Feature useful on certain occasions

• When vehicle is being operated on racetrack

• System Requirements– ESC automatically turns back on when

ignition is turned off and then on again

FEDERAL MOTOR FEDERAL MOTOR VEHICLEVEHICLE

SAFETY STANDARDSAFETY STANDARD(FMVSS) NO. 126(FMVSS) NO. 126

Federal Motor Vehicle Safety Federal Motor Vehicle Safety Standard (FMVSS) No. 126Standard (FMVSS) No. 126

• FMVSS, Electronic Stability Control Systems, requires all passenger vehicles with gross vehicle weight rating less than 10,000 pounds to have ESC systems by 2012 model year

• ESC system must meet these requirements:1. Must be able to apply all four brakes

independently.• Acceleration

• ESC system must meet these requirements:2. Must be programmed to work during all

phases of driving. • Coasting

• ESC system must meet these requirements2. Must be programmed to work

during all phases of driving. • Deceleration (including braking)

SINE WITH DWELL SINE WITH DWELL TESTTEST

Sine with Dwell TestSine with Dwell Test• Standardized test to check ESC system

functionality is sine with dwell (SWD) test– Vehicle driven at 50 mph (80 km/h) on

curved course– Vehicle is held in straight ahead position for

0.5 second (500 milliseconds)

Sine with Dwell TestSine with Dwell Test• Standardized test to check ESC system

functionality is sine with dwell (SWD) test– Vehicle is then steered back onto curved

section of road• Test designed to force vehicle ESC

system to respond

Figure 108-2 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.

NAMES OF VARIOUSNAMES OF VARIOUSESC SYSTEMSESC SYSTEMS

Names of Various ESC SystemsNames of Various ESC Systems• Every manufacturer has its own name

for the ESC system• Some examples include the following:

– BMW: Dynamic Stability Control (DSC)

Names of Various ESC SystemsNames of Various ESC Systems• Some examples include the following:

– Chrysler: Electronic Stability Program (ESP)– Ford: AdvanceTrac and Interactive Vehicle

Dynamics (IVD)

Names of Various ESC SystemsNames of Various ESC Systems• Some examples include the following:

– General Motors: StabiliTrak (except Corvette—Active Handling)

– Jeep: Electronic Stability Program (ESP)– Toyota: Vehicle Dynamics Integrated

Management (VDIM) with Vehicle Stability Control (VSG)

ESC SENSORSESC SENSORS

ESC SensorsESC 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 108-4 The hand-wheel position sensor is usually located at the base of the steering column.

Figure 108-5 Hand-wheel (steering wheel) position sensor schematic.

ESC SensorsESC 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 108-6 The VS sensor information is transmitted to the EBCM by Class 2 serial data.

ESC SensorsESC Sensors• Lateral Acceleration Sensor

– Provides suspension control module with feedback regarding cornering forces

– This type of sensor called G-sensor

– Letter “G” stands for gravity– Information processed by suspension

control module

– 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

– Typically mounted in passenger compartment:

• Under front seat

• In center console

• On package shelf

Figure 108-7 A schematic showing the lateral acceleration sensor and EBCM.

ESC SensorsESC 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 SensorsESC 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 108-9 Yaw rate sensor showing the typical locations and schematic.

TRACTION CONTROLTRACTION CONTROL

Traction ControlTraction Control• Purpose and Function

– Traction control (TC) can be separate or combined with ESC system

– TC allows ABS system to control wheel spin during acceleration

Traction ControlTraction Control• Purpose and Function

– When tires lose traction during acceleration it’s called positive slip

– Low-speed (up to 30 mph) TC uses braking system to limit positive slip

Figure 108-10 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.

Traction Control Traction Control • Purpose and Function

– TC uses same wheel speed sensors as ABS– Requires additional programming in control

module

– TC also requires• Additional solenoids in hydraulic modulator

– Needed to isolate non-drive wheels from drive wheels when braking is needed to control wheel spin

– TC also requires• Pump and accumulator to generator and

store pressure for TC braking– TC works on front-wheel-drive and rear-

wheel-drive vehicles

Traction Control Traction Control • System Components

– Main controller for TC system includes one of following:

• Body control module (BCM)

• Powertrain control module (PCM)

• Antilock brake system (ABS) controller

– Controller uses inputs from several sensors• Throttle position (TP) sensor

– Controller uses inputs from several sensors• Wheel speed sensor (WSS)

– Controller uses inputs from several sensors• Engine speed (RPM)

– Controller uses inputs from several sensors• Transmission range switch

Traction Control 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

• 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

– Most TC systems can reduce positive wheel slip at all speeds

• Most use accelerator reduction and engine power reduction to limit slip before applying brakes

Figure 108-11 Wheel speed sensor information is used to monitor if a drive wheel is starting to spin.

Traction ControlTraction Control• Sequence of Events when TC system

Engaged1. Engine torque reduced for drive wheels.2. Brakes applied to slow or stop wheel

spinning.3. Low traction or TC warning light

illuminated on dash.

Figure 108-12 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.

Traction ControlTraction Control• Traction Active Lamp

– “TRAC CNTL” indicator light or “TRACTION CONTROL ACTIVE” message flashes on instrumentation when TC engaged

Traction ControlTraction Control• Traction Active Lamp

– Message alerts driver to loss of traction– Message does not indicate a fault in system

Traction ControlTraction Control• Traction Deactivation Switch

– Many vehicles have dash-mounted TC deactivation switch

– Indicator light shows when system is on or off

ESC/TC DIAGNOSISESC/TC DIAGNOSIS

ESC/TC DiagnosisESC/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 DiagnosisESC/TC Diagnosis• Usual procedure follows these steps:

– STEP 1: Verify customer concern.– STEP 2: Perform thorough visual inspection.

• Check tires are same size and tread depth

– STEP 2: Perform thorough visual inspection.• NOTE: Use a spare tire on the drive wheel

could cause the traction control and/or ESC amber warning light to flash because the controller is seeing that the smaller tire is rotating faster than the other side.

– STEP 3: Check service information for specified procedure to retrieve DTCs.

• Check related technical service bulletins

– STEP 3: Check service information for specified procedure to retrieve DTCs.

• Most vehicles require factory-brand scan tool

Figure 108-13 The use of a factory scan tool is often needed to diagnose the ESC system.

– STEP 4: Following troubleshooting procedure specified to fix root cause of problem.

• Steps usually include checking all or many of the following:

– Brake fluid level

– Wheel speed sensor resistance

– Fault with base brake system

– STEP 5: Repair the fault.– STEP 6: Road test the vehicle under same

conditions that caused the fault.

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