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A Primer on Electronic Stability Control Systems

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Jack D. Michaels Training Center Conway Arkansas

Wednesday, April 22, 2009

Ron Racine Technical Training Specialist

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Introduction This document is a primer on vehicle Electronic Stability Control Systems. It is written to educate those whom are involved and possibly practicing the art of passenger cars and light duty trucks wheel alignment. The document contains information about a new rule established on April 6, 2007 that requires light vehicles to be equipped with Electronic Stability Control Systems (ESC) The rule was established to reduce roll over crashes and the risk of death and injury resulting from these crashes.

“Department of Transportation, National Highway Traffic Safety Administration, 49 CFR Parts 571 and 585 [ Docket No. NHTSA-2007-27663] RIN: 2127-AJ77 encompasses Electronic Stability Control Systems; Controls and Displays. The document is the final rule.”

“FMVSS Part Details Actions 126 49 CFR Parts 571 & 585 Federal Motor Vehicle Safety Standards; Electronic Stability Control Systems As part of a comprehensive plan for reducing the serious risk of rollover crashes and the risk of death and serious injury in those crashes, this rule establishes Federal Motor Vehicle Safety Standard (FMVSS) No. 126 to require electronic stability control (ESC) systems on passenger cars, multipurpose passenger vehicles, trucks, and buses with a gross vehicle weight rating of 4,536 Kg (10,000 pounds) or less. ESC systems use automatic computer-controlled braking of individual wheels to assist the driver in maintaining control in critical driving situations. NHTSA estimates ESC will reduce single-vehicle crashes of passenger cars by 34% and single vehicle crashes of sport utility vehicles (SUVs) by 59%, with a much greater reduction of rollover crashes. NHTSA estimates ESC would save 5,300 to 9,600 lives and prevent 156,000 to 238,000 injuries in all types of crashes annually once all light vehicles on the road are equipped with ESC.”

The Primer also contains a database list of all vehicles manufactured since 1996 -2008 and indicates those vehicles that have ESC as standard or optional equipment, and also shows vehicles that do not offer ESC. In addition, several examples of vehicles equipped with ESC and their Steering Wheel Angle Sensor calibration method and process are included.

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Introduction

The inclusion of ESC systems will have a direct effect on how wheel service is performed. Certain precautions and additional steps may be required when performing a wheel alignment on an ESC equipped vehicle. In addition, Electronic Power Steering equipped vehicles require a more technical approach relative to wheel alignment and steering gear service. Coding, recalibrating, and resetting of sensors has now become an intricate part of wheel service. Steering system are now capable of generating trouble codes indicative of their performance. Vehicle manufacturers provide detailed troubleshooting charts to assist technicians in resolving conflicts with these systems. Alignment technicians will now have to have access to the vehicle’s data stream in order to retrieve trouble codes before repairs are performed on the vehicle and reset system critical sensors as part of the wheel alignment process.

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What is ESC?

What is ESC? Electronic stability control, or ESC, uses the speed sensors on each wheel and the ability to brake individual wheels that are the basis of antilock brakes. ESC adds a control unit that monitors steering wheel angle and vehicle rotation around the vehicle's vertical axis. This unit uses the steering and rotation information to detect that the vehicle is about to travel in a direction different from the one indicated by the steering wheel position. Then ESC automatically brakes the appropriate wheel to help the driver maintain control. In many cases engine power also is reduced. ESC systems have been utilized by European manufacturers since early 90’s.

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ESC and driver control

How ESC helps drivers maintain control: A driver loses control when the vehicle goes in a direction different from the one indicated by the position of the steering wheel. This typically occurs when a driver tries to turn very hard (swerve) or to turn on a slippery road. Then the vehicle may under steer or over steer.

When a vehicle under steers it turns less than the driver intended and continues in a forward direction because the front wheels have insufficient traction. When it over steers it turns more than the driver intended because the rear end is spinning or sliding out. ESC can prevent under steering and over steering by briefly braking the appropriate wheel. In many cases engine power also is reduced.

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ESC Compliance Date The compliance date for vehicle manufacturers consist of a phase-in starting September 1, 2008:

“ All new light vehicles must be equipped with an ESC system that meets the

requirements of the standard by September 1, 2012.” Page 3 of the FMVSS 126. Currently vehicle manufacturers equipped about 26% of model year 2006 light vehicles sold in the US with ESC. An increase to 71% is expected by model year 2011 with 100% ESC equipped vehicles by model year 2012. This applies to roadworthy vehicles with a gross weight rating of 4,536 kg (10,000 lbs) or less.

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Current vehicle ESC availability

Source: Insurance Institute for Highway Safety

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ESC major components

ESC systems utilize the ABS, TCS, and EDTC along with the steering wheel angle sensor, yaw rate and lateral acceleration sensor to minimize the float angle. Brake system pressure is monitored by a sensor. Pre ESC activation brake system pressure most be known for the ESC to perform its function. The float angle is the angle formed by the axis of the direction the driver is pointing the vehicle (steering wheel angle sensor information) and the axis of the actual vehicle direction (sensed by the yaw rate sensor). The ESC’s function is to reduce the float angle by activating braking, throttle and transmission.

Source: Driving Stability Systems, Robert Bosch, April 2005, ISBN-3-86522-085-1

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ESC system interaction

ESP® systems assists the driver in just about every critical driving situation. Including emergency and partial braking maneuvers and incipient skidding incidents, which the system rapidly identifies and reduces in severity by timely, targeted braking of individual wheels. Driving safety is significantly increased by this active support of the driver during tricky maneuvers where there is risk of skidding. Additionally, ESP® also stabilizes the vehicle during normal braking, starting off and accelerating, since it also includes the functions of the ABS anti-lock braking system and the TCS traction control system.

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SWAS Steering Wheel Angle Sensors Steering wheel angle sensors are a critical component of the ESC systems. They inform the ESC computer of the direction the vehicle is being pointed to.

Source: Robert Bosch, Chassis Systems Control


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SWAS Steering Wheel Angle Sensors

The LWS5 is an improved product. The functional principle of the LWS-5 sensors relies on two resistance bridges positioned at 90 degrees to each other, the bridge parts consisting of GMR (Giant Magneto Resistance) elements. In the simple version, when the steering wheel is turned, a measurement cog wheel rotates over a GMR element. An integrated microcontroller uses the change in the bridge voltage to accurately calculate a steering angle of up to ± 90 degrees. No external control unit is required. The LWS 5 version is used for measuring larger steering angles; it has not one, but two, measuring cog wheels with a differing number of teeth. This expands the precise range of measurement (according to the Nonius process) to ± 780 Grad, which allows more than four complete turns of a steering rod to be measured.


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Yaw Rate Sensor Vehicle with steering wheel angle sensor calibration requirements

Vehicles with steering wheel angle sensor and yaw rate sensor calibration requirements

Toyota yaw rate sensor


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1991 Acura NSX Electronic power steering rack, notice the electric motor mounted on the rack to provide power assist when needed. Steering position calibration reset is require on these

vehicles


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Examples of vehicles with ESC Vehicle with steering wheel angle sensor calibration requirements



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Note item line 15 and the note below it.


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2008 TOYOTA YARIS The Toyota Yaris utilizes a steering motor in lieu of hydraulic power assist.

Steering center point adjustment must be perform following repairs.


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2008 TOYOTA YARIS EPS troubleshooting chart example


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Examples of vehicles with ESC

Vehicle with steering wheel angle sensor calibration requirements Vehicles with steering wheel angle sensor and yaw rate sensor calibration requirements

2008 TOYOTA Yaris

2008 Toyota Yaris Electronic Power Steering

Electric assist motor mounted directly on steering column. No hydraulic pump, fluids, or hydraulic lines.


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2008 TOYOTA YARIS

In addition to steering wheel angle sensor information, the ECU can output several data trouble codes. The scan tool should be able to retrieve and display the trouble codes.


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1998 BMW 5 Series BMW vehicles equipped with DSC systems require a steering wheel angle sensor recalibration after working on the alignment geometry. The SWAS sensor on BMW vehicles remains fully active even with the key OFF and engine OFF. The angle of the steering wheel is known at all times.


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1998 BMW 5 Series

BMW 5 Series SWAS calibration instructions. These types of vehicles require coding in addition to calibration.


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Vehicles with steering wheel angle sensor and yaw rate sensor calibration requirements Volkswagen steering wheel angle calibration procedure using Scan tool.

This procedure details how to perform the zero position calibration for the Steering Angle Sensor (G85) in many VW/Audi vehicles equipped with ESP (Electronic Stability Program). This procedure should be performed when vehicle alignment is performed or if any of the following components have been removed or replaced:

• ABS/EDL/ASR/ESP control unit (J104) • Steering Angle Sensor (G85) • Steering Column

There are certain test conditions that must be met before doing this procedure:

• Start the vehicle. • Turn the steering wheel one turn to the right and one turn to the left. • Drive in a short distance straight line on a level surface at a speed not higher than 20

km/h. • If the steering wheel is straight during the test drive then stop the vehicle with the

wheels pointed straight • Ensure that the steering wheel is not moved again. • Keep the engine running and do not switch off the ignition.

Procedure for performing the zero position calibration for the Steering Angle Sensor (G85) on VW Golf, GTI, Jetta, and Audi TT:

[Select] [03 - ABS Brakes] [Login - 11] Enter 40168 [Do It!] [Basic Settings - 04] Group 060 [Go!]

This will store the zero (centered) position of the steering wheel. There should be a displayed message that reads: "Steer. angle sender compens OK". If you get an error, it may mean the Login was not successfully performed.

Click the [Done, Go Back] button and you're all set.


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Vehicles with steering wheel angle sensor and yaw rate sensor calibration requirements Volkswagen steering wheel angle calibration procedure using Scan tool.

Procedure for performing the zero position calibration for the Steering Angle Sensor (G85) on VW Passat and Audi A4/S4, A6/S6, and A8/S8:

[Select] [03 - ABS Brakes] [Login - 11] Enter 40168 [Do It!] [Basic Settings - 04] Group 001 [Go!]

This will store the zero (centered) position of the steering wheel. There should be a displayed message that reads: "Steer. angle sender compens OK". If you get an error, it may mean the Login was not successfully performed.

Click the [Done, Go Back] button and you're all set.

The Volkswagen procedure requires entering a code 40168 in order to proceed with the calibration.


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Vehicles Manufactures with ESC

Product names

Electronic stability control (ESC) is the generic term recognized by the Society of Automotive Engineers and other authorities. 54 different vehicle manufacturers provide stability control systems either standard or optional.

Vehicle Manufacturer System ID | System Trade Name

1. Acura: Vehicle Stability Assist (VSA) 2. Alfa Romeo: Vehicle Dynamic Control (VDC) 3. Audi: ESP - Electronic Stability Program 4. Bentley: ESP - Electronic Stability Program 5. Bugatti: ESP - Electronic Stability Program 6. Buick: StabiliTrak 7. BMW: Dynamic Stability Control (DSC) 8. Cadillac: StabiliTrak & Active Front Steering (AFS) 9. Chery Automobile: Electronic Stability Program 10. Chevrolet: StabiliTrak; Active Handling (Corvette only) 11. Chrysler: Electronic Stability Program (ESP) 12. Citroën: Electronic Stability Program (ESP) 13. Dodge: Electronic Stability Program (ESP) 14. Daimler: Electronic Stability Program (ESP) 15. Fiat: Electronic Stability Program (ESP)

a. Vehicle Dynamic Control (VDC) 16. Ferrari: Controllo Stabilità (CST) 17. Ford: AdvanceTrac with Roll Stability Control

a. (RSC) and Interactive Vehicle Dynamics (IVD) and Electronic Stability Program (ESP); Dynamic Stability Control (DSC) (Australia only)

18. General Motors: StabiliTrak 19. Honda: Electronic Stability Control (ESC)

a. Vehicle Stability Assist (VSA) and Electronic Stability Program (ESP)

20. Holden: Electronic Stability Program (ESP) 21. Hyundai: Electronic Stability Program (ESP)

a. Electronic Stability Control (ESC), and Vehicle Stability Assist (VSA)

22. Infiniti: Vehicle Dynamic Control (VDC) 23. Jaguar: Dynamic Stability Control (DSC) 24. Jeep: Electronic Stability Program (ESP)


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Vehicles Manufactures with ESC

25. Kia: Electronic Stability Control (ESC) a. Electronic Stability Program (ESP)

26. Lamborghini: ESP - Electronic Stability Program 27. Land Rover: Dynamic Stability Control (DSC) 28. Lexus: Vehicle Dynamics Integrated Management

a. (VDIM) with Vehicle Stability Control (VSC) and Traction Control (TRAC) systems

29. Lincoln: AdvanceTrac 30. Maserati: Maserati Stability Program (MSP) 31. Mazda: Dynamic Stability Control (DSC) (Including

a. Dynamic Traction Control) 32. Mercedes-Benz (co-inventor): Electronic Stability Program (ESP) 33. Mercury: AdvanceTrac 34. MINI: Dynamic Stability Control 35. Mitsubishi: Active Skid and Traction Control MULTIMODE

a. Active Stability Control (ASC) 36. Nissan: Vehicle Dynamic Control (VDC) 37. Oldsmobile: Precision Control System (PCS) 38. Opel: Electronic Stability Program (ESP) 39. Peugeot: Electronic Stability Program (ESP) 40. Pontiac: StabiliTrak 41. Porsche: Porsche Stability Management (PSM) 42. Renault: Electronic Stability Program (ESP) 43. Rover Group: Dynamic Stability Control (DSC) 44. Saab: Electronic Stability Program 45. Saturn: StabiliTrak 46. SEAT: ESP Electronic Stability Program 47. Škoda: ESP - Electronic Stability Program 48. Smart: Electronic Stability Program (ESP) 49. Subaru: Vehicle Dynamics Control Systems (VDCS) 50. Suzuki: Electronic Stability Program (ESP) 51. Toyota: Vehicle Dynamics Integrated Management

a. (VDIM) with Vehicle Stability Control (VSC) 52. Vauxhall: Electronic Stability Program (ESP) 53. Volvo: Dynamic Stability and Traction Control (DSTC) 54. Volkswagen: ESP - Electronic Stability Program


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ESC system manufacturers There are approximately 12 ESC manufacturers. Some of them manufacture complete systems and other manufacture components.

1. Robert Bosch GmbH 2. Aisin Advics 3. Bendix Corporation 4. Continental Automotive Systems 5. Delphi 6. Hitachi 7. ITT Automotive, since 1998 part of Continental AG 8. Mando Corporation 9. Nissin Kogyo 10. Teves, now part of Continental AG 11. TRW 12. WABCO 13.


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ESC SWAS Calibration

Some vehicles equipped with ESC systems require recalibrating the steering wheel angle sensor, yaw rate sensor, lateral acceleration sensor, and brake pressure sensor after working on the alignment geometry.

Calibration requires connecting to the vehicles data link using a scan tool or other means.

Here is an example of a 2008 Toyota Avalon. The steering wheel angle sensor is being calibrated using a Snap-on Solus and a John Bean V3D2. The vehicle is steered straight ahead and the sensor is calibrated.

It is not necessary to drive the vehicle in order to obtain straight ahead, the aligner can provide that information by steering to equalizing front toe.


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ESC SWAS Calibration

The scan tool displays selected model information as well as the necessary instructions to calibrate the sensors.

This capability is available on Snap-on’s scanners. It is not necessary to connect the aligner to the vehicle to perform this task.