BY BOB PATTENGALE. Photoillustration: Harold Perry; photos: Jupiter Images & Wieck Media

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Dwight Foster
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1 42 June 2008

ESCAPE ROUTE BY BOB PATTENGALE Photoillustration: Harold Perry; photos: Jupiter Images & Wieck Media Electronic stability control will be a mandatory safety system on 2012 passenger vehicles, but it

2 ESCAPE ROUTE BY BOB PATTENGALE Photoillustration: Harold Perry; photos: Jupiter Images & Wieck Media Electronic stability control will be a mandatory safety system on 2012 passenger vehicles, but it s already standard or an optional feature on a large percentage of cars and SUVs. It s time to ramp up your diagnostic proficiency on this evolving technology. According to a study done by the Insurance Institute for Highway Safety (IIHS), electronic stability control (ESC) technology offers the second greatest improvement in vehicle safety, after the safety belt. The study showed that outfitting vehicles with ESC would help reduce the number of fatal accidents by approximately 41% and the number of single-vehicle accidents with fatal consequences by 56%. Numerous studies around the world confirm that ESC saves lives, which is driving the vehicle manufacturers to equip all vehicles with ESC technology as soon as possible. The National Highway Transportation and Safety Administration (NHTSA) has reacted positively to this technology and passed legislation requiring 100% ESC coverage for all 2012 light vehicles under 10,000 lbs. NHTSA anticipates that ESC would substantially reduce rollover crash fatalities by 50%, which translates to approximately 5000 lives being saved. Electronic stability control is an extension of the antilock braking system (ABS). It helps prevent skidding or spinning while cornering. ESC controls ABS and engine power output to help keep the vehicle traveling in the intended direction, even if the driver enters a turn too fast or steers the vehicle too sharply for road conditions. Manufacturers are equipping vehicles with a variety of ESC systems and marketing them under different June

For example, Audi, Mercedes and Volkswagen call their systems Electronic Stability Program (ESP), BMW and Jaguar use Dynamic Stability Control (DSC), Lexus and Toyota use Vehicle Stability Control

3 B A Most ESC systems have similar layouts, but the names vary from manufacturer to manufacturer. This image shows the standard ESP (Electronic Stability Program) configuration from Bosch. names. For example, Audi, Mercedes and Volkswagen call their systems Electronic Stability Program (ESP), BMW and Jaguar use Dynamic Stability Control (DSC), Lexus and Toyota use Vehicle Stability Control (VSC) with Vehicle Dynamics Integrated Management (VDIM), Cadillac uses StabiliTrak and Volvo uses Dynamic Stability and Traction Control (DSTC). For the sake of uniformity and clarity, we ll use the term electronic stability control (ESC) to describe all of these systems. ESC also opens the door to many other innovative technologies. Hydraulic Brake Assist, Controlled Deceleration for Parking Brake, Hill Hold Control, Hill Descent Control, Controlled Deceleration for Driver Assistance Systems, Hydraulic Fading Compensation, Hydraulic Rear Wheel Boost and Brake Disc Wiping are several examples. Just to give you an idea of how far things have progressed on the safety front, consider the last example, Brake Disc Wiping (BDW). This technology removes splash water from the brake discs by briefly applying the brakes, which is not noticed by the driver. Some ESC control unit inputs related to BDW are the windshield wiper signal, ambient A typical ESC system uses existing ABS components, but adds a steering angle sensor and yaw rate and deceleration sensors to help maintain stability control. Illustration courtesy Robert Bosch Photo courtesy Robert Bosch temperature sensor and rain sensor. The key point here is that ESC has opened the door for this new technology. The photo below shows a typical mix of the actual components that make up an ESC system. ESC utilizes the traditional antilock brake system, with speed sensors on each wheel, a hydraulic control assembly, a pump, etc., but adds a steering angle sensor, yaw rate and lateral acceleration sensors and advanced software to determine if the vehicle is about to travel in a direction different from the one indicated by driver request. The yaw rate and deceleration sensors are combined into one sensor assembly (A) normally mounted in the center console area of the vehicle. The deceleration sensor detects the rate of acceleration and deceleration in the lateral direction. It monitors the vehicle s movement on the y-axis for acceleration and deceleration and on the x- axis for side thrust. The yaw rate sensor monitors the vehicle s pivotal movement around the axis intersecting the center of the vehicle from top to bottom the z-axis. The steering angle sensor (B) detects the steering direction, angle and speed of steering wheel movement. Two basic types of sensors are used optical and magnetic resistance element (MRE). The optical sensor uses a slotted disc, light-emitting diode and photo transistor to detect movement. The MRE sensor uses two gears to detect rotational movement. The magnetic field of the MRE changes as the gears rotate, which causes the sensor resistance to change. The goal of both types of sensors is the same to accurately measure the steering wheel angle. How ESC Works Let s take a look at how ESC works to keep a vehicle under control. The illustrations on page 46 show two vehicles traveling through a right-left cornering sequence, and on a straight road with a construction vehicle blocking one lane. As labeled, the vehicle on the left in each illustration does not have ESC and the vehicle on the right is equipped with ESC. In Phase 1 in the left illustration, 44 June 2008

Vehicle Without ESP Vehicle With ESP Vehicle Without ESP, With ABS Vehicle With ESP The illustration above shows how the electronic stability control system is able to help the driver control a

The illustration on the right shows the difference between a vehicle with ABS and no ESC system and one with ABS and ESC.

4 Vehicle Without ESP Vehicle With ESP Vehicle Without ESP, With ABS Vehicle With ESP The illustration above shows how the electronic stability control system is able to help the driver control a vehicle through difficult turns. The system is capable of applying single-wheel braking to help control the vehicle. The illustration on the right shows the difference between a vehicle with ABS and no ESC system and one with ABS and ESC. ABS works well in straight-line brake applications, but does not provide the added stability on turns. both drivers approach the right-hand corner and begin turning the steering wheel. The vehicle without ESC will rely on normal suspension, tire quality and driver skill to make the corner. The vehicle with ESC is prepared to assist the driver if conditions exceed the vehicle s normal capabilities. In the case of ESC, as soon as the driver turns the steering wheel, the ESC control unit knows, via the steering angle sensor, the direction of travel and how severe the turn will be. The ESC control unit uses additional sensor inputs, including actual yaw rate and target yaw rate, to make decisions. If the actual yaw rate exceeds the target yaw rate, the ESC system takes action to keep the vehicle stable. From Phase 1 to Phase 2, the driver of the vehicle without ESC approaches the corner and attempts to make a controlled turn. The vehicle is tracking well around the first corner, but when the driver attempts to negotiate the next turn, countersteer comes into play and the vehicle skids out of control. This is just one possible scenario. If the speed of the vehicle were too great entering the turn, the driver might engage the brakes at the last second, which creates a different issue. If the vehicle is not able to make the turn, an understeer condition will likely occur, sending the vehicle into the other lane. The vehicle with ESC is a different story. From Phase 1 to Phase 2, the ESCequipped vehicle s control unit uses its sensor inputs to determine the vehicle s handling capabilities in specific situations. It s important to note that the ESC control unit does not know if the vehicle has bald tires, worn suspension parts or poor quality brakes; it can only assume optimum conditions. In this case, the ESC control unit determines that the situation exceeds the vehicle s normal capabilities and takes action. In the next phase, the ESC control unit applies the left front brake, helping the vehicle and driver navigate the corner in a controlled manner. And the ESC system is not finished. In Phase 4, the right front brake is applied to help prevent an understeer condition during the right-toleft turn. It s easy to see how ESC can make a big difference in safe vehicle handling. Now let s look at the difference between a vehicle with ABS and no ESC and one equipped with ABS and ESC. Illustrations courtesy Robert Bosch 46 June 2008

The fourth image from the bottom shows the rear end of the vehicle kicking out and the driver fighting to keep control throughout the stop. The vehicle with ESC is a different story.

5 The right illustration shows a vehicle approaching a stopped construction vehicle, requiring an aggressive stop with steering navigation. The vehicle without ESC will use the antilock braking system to help stop the vehicle, but cannot help with steering control. The fourth image from the bottom shows the rear end of the vehicle kicking out and the driver fighting to keep control throughout the stop. The vehicle with ESC is a different story. Here, the ABS kicks in, but the ESC system determines the vehicle might lose steering control and takes action. The second image from the bottom shows the ESC system releasing the left front brake slightly, which helps ESC systems are going to create additional service issues. For example, if you perform an alignment on a 2008 Toyota Highlander (above) with VSC, a zero calibration must be performed as a final step. The various steering parameters are shown in the screen capture below. the vehicle and driver stay in control. Once again, the ESC system isn t finished. The fourth image from the bottom shows the ESC system releasing pressure to the right front brake, which keeps the rear of the vehicle in check. Also, note that the vehicle with ESC stopped in a shorter distance. ESC is just one of many new collision avoidance technologies being considered. Perhaps you ve seen the Toyota commercials about self-pacing or adaptive cruise control, which utilizes the ESC system to slow the vehicle down, but what about lane departure technology? In the case of Infiniti, if the lane departure forward viewing camera determines the driver is allowing the vehicle to drift into the left lane, the vehicle engages the right side brakes using ESC, creating a slight drag, which moves the vehicle back into the correct position. The benefits of ESC technology are undisputed and the rate of availability is increasing. A recent study documented 2008 model year ESC availability, either as standard or optional equipment. SUVs offered 96% availability, cars 83% and pickups 33%. If you haven t already, you d better start thinking about preparing to service these systems. Some will say this is new-vehicle technology that s still under warranty, and we won t be seeing this in our service bays for a few years. Are you sure? If you re in the alignment business, you need to take a closer look at ESC technology. Did you know that after performing an alignment on a VSCequipped Toyota/Lexus vehicle that a zero point calibration must be performed? What is a zero point calibration? The steering angle sensor and yaw rate/deceleration sensors are critical for proper operation and must be zeroed after wheel alignment for correct operation. If you replace a steering angle sensor on most ESC systems, the vehicle control unit must learn the steering angle zero point. The photo above left shows a 2008 Toyota Highlander with a VSC system and the steering wheel in the straightahead position. The screen capture from the scan tool shows the steering angle at 0. The actual position of the 48 June 2008

As we look ahead to steer-by-wire technology, a sensor that s not properly calibrated might cause an alignment drift or pull.

6 steering sensor is 31. The zero steering parameter shows an adjustment of 31. If you had just completed an alignment and did not perform the zero point calibration, the steering angle sensor would be off by 31. As we look ahead to steer-by-wire technology, a sensor that s not properly calibrated might cause an alignment drift or pull. Diagnosing ESC systems requires the use of a scan tool and the appropriate software. These are the parameters available on a 2008 Toyota Highlander. In this case, 84 different inputs and outputs are available. ESC systems are designed with many bidirectional controls, function tests and system tests. This screen capture from the Bosch KTS-570 shows a few of the options available that are designed to help technicians diagnose these systems. ESC s Self-Diagnostic & Fail-Safe Capabilities ESC systems are designed with significant self-diagnostic and fail-safe capabilities. If something is wrong with the system, the driver will be alerted immediately. Your eyes into the ESC system are your scan tool. The screen capture at left shows the scan tool parameters available on the 2008 Toyota Highlander. As you can see, the VSC module uses a significant number of sensor inputs and output commands 84 of them! to control the system. As you look at these scan tool parameters and begin your diagnostic process, consider the source of the information. What do I mean by this? It s important to look at a system diagram or wiring diagram to fully understand the system. The point is that the problem you re attempting to diagnose in the ESC system may be caused by another system. Let s say, for example, you re diagnosing an intermittent DTC U0126 (Lost Communication with Steering Angle Sensor Module). The steering angle sensor on most ESC systems is wired directly into the controller area network (CAN). If this was the only code present, your primary focus would be the steering angle sensor and issues associated solely with that sensor. One of the steps might be monitoring the steering angle sensor input while performing a wiggle test or rotating the steering wheel back and forth. Consider a different scenario. In addition to the U0126 just discussed, additional codes are present: U0100 (Lost Communication with ECM/PCM), U0123 (Lost Communication with Yaw Rate Sensor Module) and U0124 (Lost Communication with Lateral Acceleration Sensor Module). The direction of the diagnosis might focus on issues related to the CAN network. Is there something causing issues with the CAN network? At this point you might want to check for codes in other CAN modules, just to verify if the issue is a global CAN network issue or isolated to the ESC system. It s important to look at the big picture. ESC systems are also equipped with a variety of system tests, function tests 50 June 2008

7 and bidirectional controls. The screen capture at the bottom of page 50 shows some of the items that may be available on a scan tool. If you re servicing the hydraulic system or replacing a brake caliper, pump, solenoid, etc., the brake bleeding function is a must. The capture also shows the options to test the automatic slip reduction (ASR), which tests the transmission slip operation. The static test and pulse-wheel test allow you to test the ESC system in the service bay. Steering angle initialization performs the zero calibration function for the steering angle sensor. Variant coding relates to configuring a replacement ESC module. For example, Bosch produces ESC modules that can be used on a variety of vehicles with different options. The variant code tells the ESC module how a particular vehicle is configured. Again, this is critical to complete the repair. ESC s Future Is (Almost) Now ESC systems are going to become more sophisticated in design and function. High-speed CAN networks will allow engineers to design additional features into ESC systems. Right now, many ABS, traction control and ESC systems work independently. Future vehicle systems will integrate all of them into one vehicle stability package. Newer Toyota VSC systems use VDIM to integrate brake-related functions, electronically controlled transmission and electronically controlled power steering, all to fine-tune stability control. For example, early VSC systems had to rely on the driver applying brakes and cutting engine power to control the vehicle. The VDIM system with electronically controlled power steering can alter steering control slightly, taking some pressure off the other systems. If you re into new technology, it doesn t get much better than this. We ve been seeing many innovations added to vehicles. Are you ready for this new technology? Technicians who are able to repair electronic stability control systems will be in great demand. You might want to consider spending a few dollars and visiting some of the factory service information websites. Many of the vehicle manufacturers have posted training information on these sites. For example, Toyota has a training section that includes manuals and videos. Becoming an expert at diagnosing and repairing the new ESC systems you ll be seeing soon means becoming familiar with them. The information is out there if you take the time to look. This article can be found online at Circle #22 52 June 2008

Acustomer calls and says that an ADVANCED DRIVER ASSISTANCE SYSTEMS WHAT YOU SHOULD KNOW ABOUT

Acustomer calls and says that an ADVANCED DRIVER ASSISTANCE SYSTEMS WHAT YOU SHOULD KNOW ABOUT WHAT YOU SHOULD KNOW ABOUT ADVANCED DRIVER ASSISTANCE SYSTEMS BY BOB PATTENGALE The driving public may not be quite ready for Google s autonomous vehicle, but other advanced driver assistance systems,