Tech Stuff

Vehicle stability control systems: An overview of the integrated system that enhances braking, traction and skid control

Bosch refers to their system as ESP (Electronic Stability Program).
<p>Bosch refers to their system as ESP (Electronic Stability Program).</p>

Leon serves as one of the leading technical editors for Mitchell1. He is a graduate of Universal Technical Institute and has previously worked for Aamco Transmissions and as a mobile mechanic. He holds 609 Certification and specializes in automotive diagnostics.

Vehicle stability control systems (VSC) were created to help reduce the amount of wheel slip during acceleration and in harsh driving conditions. Typically for today’s high-torque engines, a form of wheel slip regulation or traction control can increase both safety and comfort, particularly on slippery roads. It allows for smooth starts and acceleration through all speed ranges without wheel-spin or fishtailing, it also reduces the amount of oversteer and understeer when cornering. So if your customer is driving like he stole it and happens to look at his dash and sees a stability control light suddenly illuminate for a second or two, he shouldn’t worry. This just means he has just taken advantage of the stability control system.

The way stability control systems work is by having a partnership between the live sensors and the anti-lock brake unit. It works by the sensors gathering information and processing it through the computer and sending it to the anti-lock brake system (ABS) unit. All of this information is processed in milliseconds. By applying hydraulic pressure through the anti-lock brake system, it can alter the traction of the wheels individually. The ABS system works by directing the amount of brake fluid to each individual wheel by the use of valves in the ABS system. Every manufacturer incorporates different sensors to make up their own version of a stability control system, but it all starts with the ABS system.

Steering angle sensor, vehicle speed sensor, wheel speed sensor, lateral acceleration sensor, brake pressure sensor and yaw rate sensor and computer or ECU are the basics for most stability control systems. Some of the more sophisticated systems adjust the throttle electronically, even limiting the number of cylinders in use while also using the ABS system to limit wheel slip.    

A vehicle stability control system also aids in maintaining control during quick/evasive maneuvers where loss of traction would otherwise result in loss of directional control.
<p>A vehicle stability control system also aids in maintaining control  during quick/evasive maneuvers where loss of traction would otherwise  result in loss of directional control.</p>

Audi uses a system called Acceleration Slip Regulation (ASR). ASR works with the electronic accelerator and uses components of the ABS. If one wheel suddenly begins to rotate faster than the others (wheel slip), ASR intervenes in the engine management system and reduces power until the wheel stops spinning (this system also works with the electronic differential lock (EDL)). Citing another example, BMW uses a sub system called Dynamic Traction Control (DTC), which is a partner to Dynamic Stability Control (DSC). When driving on loose gravel or snow, activating DTC increases traction by allowing for more wheel slip while only enabling the DSC system when needed, and if desired DSC can be deactivated completely.

Drivers who desire a sportier driving style can activate DTC to allow for more wheel slip or drift.

Believe it or not, sound can also affect the way your customers drive. Mitsubishi is the manufacturer of the Lancer Evolution, a car known for its ability to handle just about any road in its path, by listening. The active stability control system (ASC) on the Evo operates differently from conventional brake systems. The difference is that the ASC system monitors sounds, sensations and vehicle performance. Noise monitoring was introduced as another method to “see” and in this case hear what is happening while the car is driven, it works with the other sensors to provide valuable live data.

For example let’s say your customer hears a loud clunk while driving. In that moment, the sound monitors would send a signal to the computer to check all systems to check for possible malfunctions.


Diagnostic trouble codes (DTCs) are set under different conditions, depending on the malfunction detected. Most DTCs will only be set during vehicle operation. Some DTCs will also be set during the self-check immediately after the engine is started. Most of the time when a warning light turns on for the traction control system it is due to a failed sensor. Some of the most common traction control system failures include:

Malfunction of wheel speed sensors, steering wheel angle sensor, lateral sensor, vehicle speed sensor.

Damaged wiring harness and connectors.

ABS-ECU malfunction.

To further evaluate an illuminating Traction Control Light:

1. Gather information about the problem. (Ask your customer when does the problem occur? Only occurs in certain conditions?)

2. Verify that the condition described exists. (Check for visual signs.)

3. Check the vehicle for any DTCs.

4. If you can verify the condition but there are no DTCs, or the system cannot communicate with the scan tool, check that the basic brake system is operating properly.

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