As I understand it, Volkswagen had software to artificially enhance their efficiency ratings on a test rig. Since it would only be active under test, what is the point of recalling millions of cars to remove software that will never be run?

I can see a lot of hassle and uncertainty for the owners.

  • We should add a "German Engineering" tag for questions like these :D
    – rana
    Oct 15, 2015 at 19:17
  • Related question at Engineering.SE: How was Volkswagen able to trick the lab pollution test? Oct 15, 2015 at 21:28
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    You have it backwards - they made their cars 'cleaner' during testing (with the cheat device) and were dirtier, more powerful and more fuel efficient with the cheat device off during normal driving.
    – CramerTV
    Oct 15, 2015 at 22:43
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    In a sentence: They artificially enhanced their efficiency ratings on a test rig, so now they're required to have that level of efficiency all the time, because that's what was tested.
    – user253751
    Oct 16, 2015 at 3:00
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    @DmitryGrigoryev I suspect it'll be a simple case of "if you don't get the patch installed, your car will fail the annual roadworthyness/emissions test". Unless you happen to live in a country/state that doesn't regularly test vehicles, in which case you're free to carry on!
    – Nick C
    Oct 19, 2015 at 9:19

3 Answers 3


The recall is not to remove the cheating logic; it is to actually make the engines meet emissions requirements so they do not violate the law any more. From Autoblog's initial article on the scandal:

Volkswagen intentionally installed software in nearly a half-million diesel vehicles that helped the cars evade substandard results on emissions tests, the federal government charged Friday.

The Environmental Protection Agency issued a notice of violation to the German automaker, saying the company's software broke the law by violating two provisions in the Clean Air Act. Circumventing the standards meant affected cars emitted as much as 40 times the allowable level of certain pollutants.

Both the EPA and California Air Resources Board have launched investigations. In its notice of violations, the EPA said Volkswagen officials admitted to installing and concealing what they call a "defeat device," which was designed to detect when the cars were undergoing official emissions tests – and only turn on emissions controls during that time.

Some articles have suggested that the affected engines need more than just a software patch; hardware changes will be required (emphasis my own):

According to Automotive News citing Reuters, two remedies to cover different NOx-reducing systems could be necessary, and both potentially affect performance.

Earlier examples of the EA 189 diesel engine used a lean NOx trap to reduce the harmful material coming from the tailpipe. According to experts in the Automotive News report, a software update might allow the engines to achieve compliance, but that could affect fuel economy. VW already tried this route once before the scandal came to light, but tests by the California Air Resources Board still showed the figures were too high.

Later, some of the 2.0 TDI engines began using Selective Catalytic Reduction that reduced NOx by injecting a urea solution into the exhaust stream. According to Automotive News, a software update for this equipment might increase the amount of the substance used. Not only would that mean topping up the fluid more often, but there still could be some reduction in fuel economy. But, since the 2-liter, 4-cylinder TDI engine that sits inside the diesel vehicles first mentioned as being affected by the issue in the US don't have a urea treatment system, VW would need to install them into these cars.

The irony of this whole episode is that regulatory compliance would have been far, far cheaper.

  • I agree that it would almost have to be software and hardware updates. They clearly did this for a reason, probably to save costs initially, though it's clear now that they would be better off to have been in compliance from the beginning. If it was a simple software update to bring it to regulations, it would have been much cheaper to just do that rather than program the car to cheat the test. Oct 15, 2015 at 18:49
  • @PoissonFish Indeed, $335 per vehicle suddenly doesn't sound like a lot of money any more.
    – Zaid
    Oct 15, 2015 at 18:54
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    @Zaid The $335 number doesn't take into account how many extra vehicles were bought because of VW's "clean diesel" marketing campaign. Now on the flip side, you have to take into account how many sales they have lost from this PR fiasco. So it's probably costing them a ton more than $335 in car parts. Oct 15, 2015 at 23:53

The way I understand the issue, VW wanted to increase performance and fuel mileage. The easiest route was to allow the car to pollute more. This was not possible while meeting the stringent emission standards

So they developed software that would allow the vehicle to pass the emission requirements only while in test mode. Then essentially alter the emission parameters during everyday driving to achieve more performance and better fuel economy. And they got caught.

I am sure there is a team of lawyers trying to figure out how to compensate owners for the reduced economy and performance they will get for the rest of the vehicles' life. Not to mention reduced value as the vehicles now have a tarnished reputation.

  • Think lemonade, not lemons. The value will increase as savvy consumers seek out these cars because they have better performance! Oct 18, 2015 at 13:48

The problem is they are running on an illegal tune. It is running all the time. They need to detune the vehicles so they will run within spec, or they will face greater penalties.

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