Insights on SIL, HIL, and the Pitfalls of Single Approach

Automotive Testing Best Practices: SIL, HIL, and Why a Single Approach Falls Short

by Jon M Quigley

As someone deeply engaged in automotive product development and testing, I believe that robust strategies using both software-in-the-loop (SIL) and hardware-in-the-loop (HIL) are essential. Drawing on the insights and frameworks of Jon M. Quigley, I want to explore not only the common perspectives on SIL and HIL, but also the real limitations that come from relying on a single approach to automotive engineering. This blog post is in response to a LinkedIn post.

I have written a few articles, including one not yet out on HIL for Automotive Testing Technology International. I am exploring attending their next event, the Automotive Testing Expo North America, which will take place in Novi, Michigan, in November. If you’re attending, please let me know you would like to meet there and discuss product testing. Perhaps we can give away a book or two of the automotive testing dictionary.

Why a Single Approach to Automotive Testing Is Not Enough

In my experience, depending on a single approach in testing is risky. Modern vehicles are intricate systems, and a single testing method can create blind spots, leaving critical issues undetected. Real-world automotive environments are full of unpredictable interactions that a single approach can’t simulate or validate.

Over the years, I’ve seen teams fall into the trap of thinking that just increasing test counts or focusing on compliance testing is sufficient, but Quigley reminds us that testing needs to be multi-layered. His frameworks, like the Automotive Testing Efficiency Framework (ATEF), showcase how efficiency isn’t about any single approach or tool, but about maturing the whole process and integrating a variety of testing methods.

Software-in-the-Loop (SIL): My Take

What SIL Offers and Why It’s So Commonly Used

I’ve used software-in-the-loop (SIL) frequently as an early-stage and cost-effective way to validate embedded automotive software. SIL is great for rapid bug detection, reducing our dependence on expensive physical prototypes, and allowing us to investigate a wide range of scenarios virtually.

My Perspective on SIL

There is plenty of value in the use of SIL, but an important caveat: SIL should never be viewed as a silver bullet. I stress that while SIL provides significant early feedback, it can’t detect hardware-based defects, subtle integration issues, or real-world variability.

The SIL use approach in most projects is to make it part of a broader, strategy-driven approach. I ensure our SIL efforts are traceable, involve multiple disciplines, and fit into a feedback-rich process—focused and in line with continuous improvement and cross-functional teamwork.

Hardware-in-the-Loop (HIL): Strengthening the Testing Toolbox

Why I Rely on HIL

Hardware-in-the-loop (HIL) takes validation a step further, letting me test actual ECUs and hardware interfaces in simulated real-world conditions. HIL is crucial for catching timing issues, electrical noise, and the kinds of integration bugs that SIL doesn’t reveal.

My Take on HIL

I champion the incorporation of HIL rigs in system development, while also noting that it’s resource-intensive. The benefit is we are able to explore system incarnations long before spending money on the prototype parts. Again, a reasonable approach is balancing HIL with other approaches—especially SIL—so we can maximize system definition quality and defect detection without blowing out time or cost constraints. Staying flexible and tool-independent with HIL setups, helps ensure our testing frameworks remain adaptive and effective.

Conclusion: Why I’ll Never Trust a Single Approach

The bottom line, in my practice, it is clear: with the growing complexity of automotive systems, no single approach—be it SIL, HIL, or any other—can guarantee product integrity or customer satisfaction. The best results come from blending methods, benchmarking practices, and investing in people and process capability. Start early by exploring system incarnations through models on HIL and SIL rigs. Only by rejecting the myth of a single approach do I deliver the safest, most reliable automotive products.