Making sense of stability control systems

Sept. 19, 2016
Your customers are blissfully unaware of how hard their stability control systems work – until they stop working!

As technicians working in the automotive field, you have no doubt experienced many different types of systems on vehicles of today. Many of those systems work separately or they work in conjunction with another system. Isn’t it great that you can turn the ignition on and see 15 or more warning indicators light up on the instrument cluster during a bulb check and then have to know what each one stands for or what system they represent? As an older technician like myself, maybe no. My internal hard drive is pretty full with not much more room for data unless I purge some and make room for new technology.   In this month’s article, I’m going to touch on Vehicle Stability Control (VSC), Electronic Stability Control (ESC), Electronic Stability Program (ESP), Dynamic Stability Control (DSC) and even Dynamic Stability and Traction Control (DSTC) systems. All these acronyms pertain to vehicle stability control systems. Each manufacturer uses a different name for their system, but the fundamentals of how the systems work are relatively the same.

What is stability control?
It’s hard to believe that vehicle stability control was found on vehicles as far back as 1987 by Toyota and Mercedes-Benz in the form of traction control. So what is vehicle stability control? It is a combination of antilock brakes, traction control and an electronic stability program combining the two. So in simple terms, if your vehicle has ESP or a VSC on board, it also provides you with two further active safety systems: the Antilock Braking System (ABS) and the Traction Control System (TCS). ABS prevents the wheels from locking during braking; TCS prevents the wheels from spinning when starting off and accelerating. While ABS and TCS intervene on a vehicle’s longitudinal dynamics, ESP or VSC additionally improve the lateral dynamics, thus ensuring stable driving in all directions. See what I mean when I said one system works in conjunction with another system?

Fig. 1: 2013 Dodge Dart Fig. 2: The Dart had multiple warning lights illumincated on the dash.
Fig. 3: Using the Chrysler Wi-Tech to see what modules are communicating. Anything in yellow has an issue. Fig. 4: Using the Chrysler Wi-Tech to perform the calibration of the dynamic sensor under miscellaneous tests.

Let’s look at how one of these systems work. General Motors calls their system ESC, also referred to as ESP or DSC, and is a computerized technology that improves a vehicle's stability by detecting and reducing loss of traction (skidding). When ESC detects loss of steering control, it automatically applies the brakes to help "steer" the vehicle where the driver intends to go. Braking is automatically applied to wheels individually, such as the outer front wheel to counter over steer or the inner rear wheel to counter under steer. Some ESC systems also reduce engine power until control is regained. ESC does not improve a vehicle's cornering performance. It helps to minimize the loss of control. For example, on a 2009 GMC Arcadia, the systems involved with stability control are the antilock brake system (ABS), the bi-state engine mount (BSM), the dynamic rear proportioning (DRP), traction control system (TCS), variable effort steering (VES) and the vehicle stability enhancement system (VSES). Just to summarize how complex some of these systems can be, the components of this system are electronic brake control module (EBCM), the brake pressure modulator valve (BPMV), the ABS pump motor, the bi-state engine mount solenoid, the brake booster vacuum sensor, the variable effort steering solenoid, a lateral accelerometer, a master cylinder pressure sensor, a steering wheel position sensor, a yaw rate sensor, four-wheel speed sensors and last but not least a traction control switch. So what’s amazing is this vehicle has six systems and 11 components that make up the stability control system, and the vehicle is seven years old already! Oh, did I forget to mention the body control module (BCM) along with the instrument cluster (IC) that control the warning indicators for the dash? I would suggest on any stability control problem you face that you read up on how the system works and who the players involved are. It’s only going to get more complicated as technology progresses.

Solving system issues – A case study
Let’s take a look at a 2013 Dodge Dart (Fig. 1) that I actually made a house call on, which just so happens to be my daughter’s vehicle. It had an ESC light, ABS light (Fig. 2) and a SRS light illuminated on the dash. The SRS light is for the airbag restraint system. On this vehicle, the ESC uses the ABS and traction control along with the Dynamic sensor and the steering angle sensor. The Dynamic sensor is incorporated into the Occupant Restraint Controller (ORC) and the steering angle sensor is located in the Electronic Power Steering (EPS) gear. Now so far we know that there are four separate systems involved with the indicator lights on the dash.

The first order of business is to hook up a scan tool to this vehicle that is capable of accessing all these system (Fig. 3). If your tool is able to do an all-system scan, then I would recommend doing that so you can see if there are any other modules that have any codes stored that pertain to the dash indicator warning lights. After doing the code scan, I noticed that there were codes in the ABS and ORC systems. The code retrieved in the ORC system was a C10CC-49, which is an internal electronic failure of the Dynamic sensor. The code stored in the ABS module is a U0125-00, which is a loss of communication with the multi-axis sensor. Here is a hint, notice that the code set in the ORC has a first digit that starts with a “C?” That typically is a chassis fault code, isn’t it? So why is the a “C” code in the airbag system? Aren’t they typically “B” codes? If you read up on the system, you would know that the stability control system is incorporated into the ORC by way of the Dynamic sensor/multi-axis sensor. This code will set in the ABS module if it does not receive a message from the Dynamic sensor within 150ms. So what we know is the ABS module isn’t receiving a data message from the ORC Dynamic sensor. Now it’s time to focus on the ORC system. But wait! Isn’t this a stability control case study, not a restraint control issue? This is why when working on today’s modern vehicles you can’t just focus on one thing right away; you need to look at the complete picture.

So getting back to our stability control issue, the Dynamic sensor measures side-to-side lateral motion and vehicle rotational sensing, which is how fast the vehicle is turning. To properly test this sensor, the service information states that the calibration procedure needs to be performed under the C006A-54 code in the anti-lock brake section. This test requires you to drive the vehicle between 5 and 15 mph turning left and right. Be careful when you do this as not to run into anything or perform this by a police officer for fear of a drunk-driving appearance. This test is located in the scan tool under miscellaneous functions (Fig. 4). If the calibration of the multi-axis sensor does not set after the second time, then the ABS module needs to be inspected for a wiring issues or plug connection problems. I inspected the ABS module and its connection and did not visually find any fault so I knew that the real culprit was the ABS module (Fig. 5). The ABS module wasn’t receiving the necessary data from the ORC even though the data was being sent to the ABS. See, a complicated ESC issue isn’t so complicated after all as long as you understand how the system works.

Another example

FIg. 5: The Dart ABS module located by the engine firewall. Fig. 6: 2003 Toyota Sequioa in the shop.
Fig. 7: This Sequioa has a VSC light on in the IP cluster. Fig. 8: 2012 Chevrolet Malibu with a stabilitrak warning message on the dash. This vehicle didn't actually have a stability control problem.
Fig. 9: Here's the cause of our stabilitrak light on the 2012 Malibu.

Working on a vehicle that has a stability control issue more often than not is caused by a fault from another system or an obvious alteration to the stability control system on the vehicle. Such was the case of a 2003 Toyota Sequoia (Fig. 6). The vehicle has a VSC light on the dash (Fig. 7). The vehicle displayed a DTC 1337 stored in the ABS module. This code is for a mismatched tire size. On vehicles with stability control, the module that controls this system has a calibration file programmed for that specific vehicle. In that program, the module reads the tire size along with a vehicle speed and some other inputs and processes that information so it can make an informed decision on what it needs to do to correctly apply the brakes and steering effort for safe operation of the vehicle. Upon inspection of the tires, I found that this vehicle should have P245/70R16 tires, which it did for three out of the four tires. The right front tire was a P265/70R16. Both of these tire sizes are correct for this vehicle; however, they all need to be the same. The P265/70R16 tire is 1.18 of an inch taller than the other size tire. The revolutions per mile at 60 mph on a P245/70R16 is 661 as opposed to the P265/70R16 which is 637.The right front wheel is actually turning 24 times less than the rest of the wheels. When the ABS module — on this vehicle it’s referred to as a skid steer ECU — receives the information from the wheel speed sensors, it will notice the difference in the wheel rotation on the right front wheel. Even though this DTC is an ABS system DTC, it will also illuminate the VSC indicator as well due to the fact that these two systems work together to control braking and steering control. The ABS system did not set a code for an erratic or malfunctioning right front wheel speed sensor because the reading was consistent. It just wasn’t correct. How the incorrect tire size was put on this vehicle is a mystery, but never the less it’s always a good practice to look over replacement parts carefully prior to installation. If you’re wondering why the ABS light is not illuminated on the dash in our photo along with the VSC indicator, it is because the indicator bulb for the ABS light was burned out. That was an additional repair added to our VSC malfunction issue.

Remember, vehicles with stability control systems work with many different players. The VSC system of our Dodge Dart is very different than that of our Toyota Sequoia, but the way the systems operate are very similar. As these systems become more complex, the method of diagnosis is still the same — that is for now.

Vehicle stability control systems have been around for a long time. They are not going to go away anytime soon. In fact, they will become more complex as technology increases. I know I have stated this before, but the best rule of thumb that I have in diagnosing any vehicle drivability or electrical problem is to know the system you're working on. Grab a cold beverage and sit down and spend a few minutes reading up on how these systems work. You will be amazed by how these systems work. You will be amazed by how much easier it will be if you have a grasp on how each component and/or system works. Remember, if you put the time in and become more proficient in tackling these types of jobs, you just might see an increase in your wallet, not to mention further driving your passion for repairing today's vehicles. And isn't that the ultimate goal?

About the Author

Edwin Hazzard | Contributor

Edwin Hazzard owns South East Mobile Tech in Charleston, S.C., a mobile diagnostic and programming service providing technical service to many automotive and body repair shops. He has 35 years’ experience in the automotive industry. He currently is an automotive trainer, board member of TST and many other automotive affiliations. 

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