Light Duty: Staying in Control

Fleets are gaining more safety options with ride stability systems.


It works by recognizing wheel skid—sensors detect the difference between the steering wheel angle and the direction the driver is actually turning by “reading” the steering wheel position 25 times a second and factoring in the amount of sideways force in play, vehicle speed and the vehicle’s response to steering wheel input.

Integrated with ABS and traction control, the system uses the brakes to enhance control of the vehicle’s direction and reduces engine torque while applying precise amounts of pressure to individual brakes to help keep the vehicle on track. These brake and engine interventions help realign the vehicle’s path with that being steered by the driver.

GM technical fellow Mike Rizzo says that, much like the other systems, StabiliTrak lays dormant until it is needed.

“It’s waiting for the vehicle to get to an evasive handling situation, then it’s providing assistance through intelligently applying brake forces independent of the driver’s foot being on the brake, to stabilize the vehicle,” Rizzo says. “(It’s) not trying to do something to the vehicle until the control algorithm determines that a wheel is skidding or the vehicle is skidding due to an evasive handling maneuver.

“Then, the system is coming on and providing assistance to regain control of the vehicle or a wheel skidding. In normal driving, you won’t even know it’s there,” he says.

Typically, StabiliTrak includes a yaw rate sensor, lateral accelerometer, steering wheel angle sensor, master cylinder pressure sensor, wheel speed sensors, and interfaces with the engine control module to control engine torque.

Systems with all-wheel drive may have a longitudinal accelerometer due to the fact you can spin all four wheels at the same time, Rizzo says, and that sensor is necessary to detect those kinds of situations.

Rizzo says the system is essentially designed to be maintenance-free, though he says issues with malfunctioning sensors can crop up on occasion. In that case, your technicians can use software to detect problems and can make repairs by reading the malfunctioning code stored in the control module.

Other than that, Rizzo says the only real maintenance is determining now long to go before changing your brake fluid. When this is the case, some care is needed.

“It’s crucial for the system, since it’s applying brakes, that when you change the brake fluid or you open up the brake system, that you use the diagnostic Tech II procedure for getting the air out of the brakes lines,” Rizzo says. “Sometimes you have that modulator sitting there, and if you open up the brake system and any air works its way back into the air modulator, doing a base brake bleed might not get rid of that air. We have a routine in our Tech II that exercises the control modules, all the valves and stuff, and pushes fluid through that, so if there’s any air in that module, it will exit and come through the bleeder screw.”

Also, Rizzo says the StabiliTrak sensors should not be moved, because they are finely tuned to respond from fixed locations.

“Relocating them, for whatever reason, would be an area of concern,” Rizzo says. “The algorithm is tuned based on where the sensors are in the van as we sell it. You definitely want to keep those sensors where they’re located and make sure they’re oriented the according to what the service manual specifies.”

According to GM, the next generation of StabiliTrak will assess the vehicle response to driver steering, acceleration and braking inputs and help steer the vehicle as necessary to maintain vehicle stability.

ADDED SECURITY

Many vans and light duty trucks are built for work purposes these days, with safety features already standard. Whether spec’ed out from your favorite OEM or added on afterwards, these ride stability systems are relatively easy for your technicians to install and maintain.

More importantly, they can help avoid accidents and keep your vehicles in better shape—saving on parts, repairs and (most importantly these days) fuel, providing an added layer of security for both your fleet and your bottom line.

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