Grounding-Related Radar Failure in an Electric Vehicle

This case study describes an EMC troubleshooting investigation into a radar module that failed to operate when mounted on an electric vehicle, despite working correctly on other platforms. The issue was traced to a grounding-related electromagnetic interference problem: unintended current division between parallel return paths caused the radar to malfunction when bonded to the vehicle chassis. We carried out targeted measurements to identify how return currents flowed and proposed an effective chassis isolation strategy to resolve the issue.

Sometimes, we are asked to solve real-world EMI issues. By “real-world,” we mean electromagnetic noise that directly affects product operation and functionality, rather than issues related to passing formal EMC compliance tests. This distinction is important, as EMC is often perceived solely through the lens of certification and test reports.

In practice, many engineers encounter noise-related problems that are difficult to explain or reproduce. In extreme cases, if these issues are not resolved, they can determine the commercial success—or failure—of the product and, in some situations, the company itself. The importance of such problems speaks for itself.

In the following case study, we demonstrate how we address these real-world EMI challenges and help companies resolve critical operational issues. One recurring observation is that engineers involved in troubleshooting do not always initially consider EMI as the root cause. As a result, the problem may not be investigated from an electromagnetic perspective until much later.

It is also worth noting that not every suspected EMI issue is actually caused by EMI. In a previous project, for example, a wind tunnel system was producing incorrect data. Our investigation helped the client rule out EMI as the cause, and the issue was ultimately traced to mechanical vibration rather than electromagnetic interference.

The case studies presented below, however, are genuinely EMI-related—and more specifically, grounding-related. Project 789 involved a radar module mounted at the front of an electric truck. The radar’s function is to detect objects ahead of the vehicle and provide collision warnings to the driver. When installed on this vehicle, however, the radar module failed to operate correctly.

The radar unit itself was supplied by Continental and had been successfully deployed on many other vehicle platforms. This strongly indicated that the issue was not with the radar module itself, but with its integration into this particular electric vehicle.

Based on experience with similar issues, our first step was to review the grounding structure of the vehicle. The vehicle did not have a well-defined or low-impedance chassis ground. The radar module includes a metal grounding stud, and the manufacturer recommends grounding the unit to the vehicle chassis. However, during the review we also identified a separate 0 V (black) conductor within the power cable.

This raised a critical question: were there now two parallel ground paths? If so, how was the return current distributed between them?

We set up measurements to monitor the return current on both grounding paths and confirmed that the current was indeed splitting between them. This unintended current division was the root cause of the malfunction.

Interestingly, when the radar module was not bonded to the vehicle chassis, it functioned correctly and reliably detected objects. However, the moment the unit was grounded to the chassis, the radar failed to operate as intended.

This case highlights how grounding—often assumed to be benign or beneficial—can become the primary cause of EMI-related functional failures if not carefully designed and validated. In this case, we can also say, the vehicle chassis is "noisy". If the chassis were well designed, then we should not have had this issue.

At the vehicle level, the available mitigation options are quite limited. Our recommendation is to isolate the ground of this unit. While it would, of course, be possible to improve the vehicle chassis grounding design, this would not be the most cost-effective solution.

A thorough risk assessment is required, as the radar manufacturer explicitly states that grounding of the unit is mandatory.