Tradecraft: The effects of an EMP on automobiles (Spoiler alert: the movies are wrong)

(TFC) – The threat of an Electromagnetic Pulse (EMP) knocking out all of the vehicles in the country is popularized by just about every sci-fi post-nuclear war movie in history. A twist is that it will only effect those vehicles with lots of electronics. These scenes are based on a public belief in what really amounts to a nuclear myth.

The United States has an EMP Commission. It has extensively studied the impacts of EMP. If your car isn’t running, it will most likely be fine. Out of 37 vehicles with electronics tested, not a single one malfunctioned. If it’s running, there will probably be some effects, but not catastrophic failures. At average EMP levels, only 3 cars stopped running. All three restarted. Other than that, it was blinking lights and minor nuisance issues. One car needed some repairs to the instrumentation in the dashboard. At higher EMP levels, it could be expected that 2 out of 3 cars would suffer some nuisance. Out of those that suffer effects, only a small fraction are expected to experience major issues like stalling.

The myth persists because of the addition of more and more electronics to automobiles as time marches on. At the same time, microprocessors have become more protected against EMPs, so the expected vulnerabilities aren’t surfacing.

The EMP commission had this to say in its 2008 report:

The potential EMP vulnerability of automobiles derives from the use of built-in electronics that support multiple automotive functions. Electronic components were first introduced into automobiles in the late 1960s. As time passed and electronics technologies evolved, electronic applications in automobiles proliferated. Modern automobiles have as many as 100 microprocessors that control virtually all functions. While electronic applications have proliferated within automobiles, so too have application standards and electromagnetic interference and electromagnetic compatibility (EMI/EMC) practices.

Thus, while it might be expected that increased EMP vulnerability would accompany the proliferated electronics applications, this trend, at least in part, is mitigated by the increased application of EMI/EMC practices. We tested a sample of 37 cars in an EMP simulation laboratory, with automobile vintages ranging from 1986 through 2002. Automobiles of these vintages include extensive electronics and represent a significant fraction of automobiles on the road today. The testing was conducted by exposing running and nonrunning automobiles to sequentially increasing EMP field intensities. If anomalous response (either temporary or permanent) was observed, the testing of that particular automobile was stopped. If no anomalous response was observed, the testing was continued up to the field intensity limits of the simulation capability (approximately 50 kV/m).

Automobiles were subjected to EMP environments under both engine turned off and engine turned on conditions. No effects were subsequently observed in those automobiles that were not turned on during EMP exposure. The most serious effect observed on running automobiles was that the motors in three cars stopped at field strengths of approximately 30 kV/m or above. In an actual EMP exposure, these vehicles would glide to a stop and require the driver to restart them. Electronics in the dashboard of one automobile were damaged and required repair. Other effects were relatively minor. Twenty-five automobiles exhibited malfunctions that could be considered only a nuisance (e.g., blinking dashboard lights) and did not require driver intervention to correct. Eight of the 37 cars tested did not exhibit any anomalous response.

Based on these test results, we expect few automobile effects at EMP field levels below 25 kV/m. Approximately 10 percent or more of the automobiles exposed to higher field levels may experience serious EMP effects, including engine stall, that require driver intervention to correct. We further expect that at least two out of three automobiles on the road will manifest some nuisance response at these higher field levels. The serious malfunctions could trigger car crashes on U.S. highways; the nuisance malfunctions could exacerbate this condition. The ultimate result of automobile EMP exposure could be triggered crashes that damage many more vehicles than are damaged by the EMP, the consequent loss of life, and multiple injuries.

In short, it’s unlikely you need to build a faraday cage in your garage to protect your vehicle.