How can centering a steering wheel during an alignment cause a vehicle to turn a blind eye?

In the past two years we have seen more vehicles on the market with stability management and adaptive cruise control. If a vehicle with one of these systems comes into your shop for alignment, be aware that any changes in the steering position sensor’s “zero” position may have drastic consequences for the safety of the vehicle. These systems use multiple inputs from different sensors to set the distance from the cars in front. If the data from one of these sensors is false, it could cause the system to go blind.

RADAR CRUISE CONTROL
Adaptive cruise control builds on the functionalities of the cruise control system and, within certain system limits, maintains the correct distance from the vehicle in front – automatically. The system uses a special radar sensor to measure the distance from the vehicle ahead. If the distance is too small, the system reduces speed moderately by easing the throttle or it automatically activates the brakes, up to approximately 25 percent of maximum vehicle deceleration. Once the road ahead is clear again, adaptive cruise control accelerates the car back up to the speed previously set.

If the braking process activated by the adaptive cruise control does not decelerate the vehicle sufficiently, an acoustic signal is triggered immediately to warn the driver to intervene manually. An outstanding feature of adaptive cruise control is its driving dynamics. The program maintains a short distance from the vehicle in front and accelerates swiftly back up to the journey speed set if the road ahead becomes clear.

Even if adaptive cruise control is activated, the driver is still responsible for monitoring his vehicle’s speed and the distance from the vehicle in front. Adaptive cruise control does not react to stationary objects or approaching vehicles.

GOING IN CIRCLES
The radar systems on these vehicles are designed to look at what it thinks is in the lane ahead while monitoring the cars in the lanes next to it. Since the radar sensor does not move, to interpret the radar signals it looks at the input from the steering position sensor. If a technician centers the steering wheel during an alignment without “zeroing out” the steering position sensor with a scan tool, it could cause some problems.

If the steering position sensor is giving a false reading, the information from the radar sensor is interpreted differently. Since the car now thinks that it is turning, the computer might think that that car in front might just be a car in the next lane over. The vehicle probably will not hit the approaching vehicle, but the driver will notice abnormal operation like rapid deceleration or brake engagement.

On these systems, the radar unit may need to be aligned. If the rear suspension is adjusted and the thrust angle is altered by damage or adjustment, the radar sensor on some Audi models may need to be adjusted with specialty tools.

It is critical that the technician look for these systems on 2004 and newer vehicles that come in for alignment. Typically, these systems are only found on high-end models from Audi, BMW and Cadillac. But, these systems are being offered on many mundane models for 2006, like the Toyota Sienna Minivan. Some aftermarket scan tools can reset the steering position sensor to zero, or at least let you read the input from the sensor to determine if there is a problem.