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According to C. Davis of the Ask a Prepper blog, after a major electromagnetic pulse:

Most electronics will be fried beyond repair and it will be years – in some cases decades – before anyone is able to start making replacements.

The blog specifically references motor vehicles.

On the other hand, Jason Torchinsky of Jalopnik claims that:

most cars would not be seriously affected

Is Torchinsky correct that if an EMP hit your city (say, from a nuclear blast), most cars would still be usable?

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  • $\begingroup$ I am finding it difficult to see how this could be an answerable question. E.g. what is a "nuclear blast"? Are we talking about a TNW or the Tsar Bomba? The distance between the city and the blast is also a giant factor, if we drop a bomb on Washington I'd rather have my car (and myself) in Beijing than NY city. $\endgroup$ – Jordy Jun 29 '17 at 6:48
  • $\begingroup$ @Jordy: He's talking about electromagnetic pulse, for which a nuclear blast is just one possible source. The question is perfectly answerable; don't get hung up on the mental picture of a giant mushroom over a devastated city. (This here is a Boeing 747 getting EMP-tested; note the very much non-nuclear EMP generator.) $\endgroup$ – DevSolar Jun 29 '17 at 8:56
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    $\begingroup$ @DevSolar, I understand what an EMP is, you missed to see the underlying argument that this claim is to vague. Here are more examples: what are "most cars"? What is "seriously affected"? And what constitutes "an EMP [that] hit your city"? EMP can come from lightning, nuclear blasts and from electric motors, one can have a more devastating effect than the other. I also bet that that Boeing of yours is getting tested under very specific conditions for very specific EMP ranges, this question needs those specifics too if you want it to be answerable in the scope of this site. $\endgroup$ – Jordy Jun 29 '17 at 9:48
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Hard to answer, since most of the information about HEMP is classified, but also because the question is too broad. Any kind of EMP is not going to affect the same a car in an underground parking than in the open, one right below the EMP source than one 2,000 miles away, one 1988 car or a 2015 car, and so on.

As a general rule, a HEMP caused by a nuclear explosion in the stratosphere can stop dead most modern cars in a large area (hundreds of miles). However, many of them can be restarted (if they don't crash as a result) or be repaired without too much hassle. You can google for articles about EMP effects on cars, such as this one but they all refer to the same report as a primary source: this study from the EMP commission, which is, to the best of my knowlegde, the only publicly available study ever made on EMP in cars.

The test was made using vintage cars from 1986 to 2005, and since they had to return the car after the tests, cars were tested starting with weak EMPs and were stopped whenever a car showed evidences of being affected. They concluded that most cars won't be affected by EMPs at all, or only suffer minor glitches (lights blinking, radio failing), but about 10% of cars could have their engines halting if surprised on the road, potentially causing accidents; however, newer cars with much more electronics and microchips may be way more vulnerable than the vintage cars that were tested.

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    $\begingroup$ HEMP? The OP dit not ask specifically for 'high altitude' $\endgroup$ – Jan Doggen Jun 29 '17 at 13:05
  • $\begingroup$ Please provide some (specific) references to support your claims. $\endgroup$ – Oddthinking Jun 29 '17 at 13:08
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    $\begingroup$ The question asked if "most cars" are going to be affected. In most American cities, most cars are above ground. You can make reasonable assumptions about where cars are. $\endgroup$ – BobTheAverage Jun 29 '17 at 15:40
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    $\begingroup$ @JanDoggen If you want an EMP which is both "major" and affects a whole city, then it must be high altitude. In any case, what I was saying is that most information about HEMP's (and particularly those caused by nuclear explosions in the stratosphere) is classified - information about EMP in general isn't. $\endgroup$ – Rekesoft Jun 30 '17 at 6:40
  • $\begingroup$ You say "newer cars with much more electronics and microchips must be way more vulnerable". The study says otherwise. Page 115, first paragraph: "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." $\endgroup$ – DevSolar Jun 30 '17 at 7:45
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Most cars will not be affected.

From the Report of the Commision to asses the thread to the United States from Electromagnetic pulse (EMP) attack

An EMP attack will certainly immediately disable a portion of the 130 million cars and 90 million trucks in operation in the United States

Approximately 10 percent of the vehicles on the road will stop, at least temporarily, thereby possibly triggering accidents, as well as congestion, at field levels above 25 kV/m

Page 115 of the report goes into more details but basically the vulnerability comes from the electronics in modern cars, however some of the effects are mitigated by improved electromagnetic interference practices/standards.

Also if the car is not running at the time of the EMP, it will probably be OK. Of those that were running the effects were mostly minor, the most significant being engine stall but really no long term effects.

The statement that an EMP will result in years of no automobiles is ludicrous.

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  • $\begingroup$ Huh, I guess I should've read Rekesoft's answer below in more details before posting my own... $\endgroup$ – ventsyv Jun 30 '17 at 16:05

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