This month, I had an opportunity to ride along in a brand-new F150 Lightning Platinum. This thing was loaded to the gills – power everything, massaging front seats, blind spot monitoring, lane keep assist, adaptive cruise control, the works! We were driving down the interstate with the truck in “self-driving mode” and it was really something to experience. The truck was using a number of ADAS sensors to monitor the vehicles around it, the curvature of the road, and everything in between. It tracked straight and kept us in the center of the lane, even as the road curved back and forth.
The whole experience left me thinking about the importance of all of the systems which make self-driving possible. From the multitude of sensors which feed data to the ADAS systems, to the mechanical systems, it’s a team effort!
Maybe it’s the technician in me, but whenever I see a new piece of technology, my first thought is usually “what will happen if this goes wrong?” In this case, my thought was “what would happen to the vehicle if the alignment wasn’t set correctly, or if someone missed a sensor calibration?”
This is a good thought exercise for all of us. It gives us an opportunity to look at how these systems operate, how they’re connected, and what could go wrong if we don’t service them properly.
I’m sure that we all have a basic understanding of alignment angles, and how they affect the way the vehicle handles. If you’re working on a vehicle that is equipped with ADAS features, you need to look at the “big picture” and really consider how the vehicle will operate if things aren’t done correctly.
These days, vehicle alignment and ADAS features are deeply interconnected. ADAS features like lane keep assist rely on data inputs from the steering angle sensor, front camera(s), and more just to monitor where the vehicle is in the lane of travel (Figure 1). Blindspot monitoring systems will use radar or lidar sensors to detect other vehicles, their distance, speed, and direction of travel.
If you need to perform a calibration on an ADAS sensor, the alignment needs to be set first. The vehicle also needs to track straight down the road. The steering angle sensor should be calibrated to the new straight-ahead position. This allows the system to accurately determine whether the driver is trying to initiate a turn, or simply drive straight down the road.
These are very basic ideas, but they can have a profound impact on the way the vehicle reacts in a variety of situations. If the thrust angle is out of spec, and/or if the steering position sensor is not properly calibrated, things can get thrown out of whack. Say you’re working on a vehicle which uses the brakes to clamp down on individual wheels for traction or stability control. If the thrust angle is out of whack on a vehicle like this, and the vehicle thinks that it’s sliding or skidding, it will squeeze the brake calipers and try to straighten itself out. But, instead, all it will be doing is wearing down the brake pads on that one corner.
I recall a repair from my career which illustrates the importance of proper alignment and ADAS calibration. A customer brought in their 2019 VW Golf Alltrack for a steering complaint. They said they had recently had a lift kit installed on the vehicle – nothing too radical, around 1-1.5”. After the lift kit was installed, they noticed that the vehicle wasn’t steering as it had before. They said it felt like they were being caught off guard by a strong crosswind on the highway, but the weather was clear and the winds were calm.
I drove the vehicle and, sure enough, on a clear day with no wind, it felt as if I was getting slammed by a strong crosswind. It was sporadic, but it was there. The first thing I did was run a system scan, but there were no stored DTCs. So, I looked at the data PIDs and was surprised to see the steering angle sensor was off by a significant amount in the straight-ahead position. I can’t recall the exact number, but it was noticeable. I drove the vehicle onto the alignment lift and my suspicions were confirmed; the alignment had been improperly set (Figure 2), and the steering angle sensor had not been recalibrated post-alignment.
So, what caused this strange steering feel? The Golf Alltrack has an electric power steering (EPS) rack. In this type of system, steering assist is actuated based on input response. The EPS system looks at data from a number of sensors throughout the vehicle to determine how much steering assist force is needed. These sensors include, but are not limited to, the steering angle sensor, steering force sensor, vehicle speed sensor, individual wheel speed sensors, yaw rate sensor, battery voltage reading, and more.
In the case of our customer, the system was seeing steering angle at all times, even when the vehicle was driving straight down the road. As soon as any steering force was detected from the driver, it applied more steering assist force than was really needed, which made it feel as if you were being surprised by a strong crosswind. We were able to center the steering wheel, set the alignment correctly, recalibrate the steering angle sensor, and all was well (Figure 3).
So, what’s the takeaway from this? Be aware of how much the ADAS features rely upon mechanical systems such as vehicle alignment and suspension setup. Always check the OEM service information for tips and tricks, and NEVER skip calibration or setup steps. Doing so can negatively impact the performance of these important systems, and could jeopardize the safety of your customers and their passengers.