The Defeat Device

What is the Defeat Device that VW installed, and how does it work?

Until VW lift the lid on how the Defeat Device works, it's difficult to say exactly what it does, and how it manages to reduce the emissions on the vehicle it is installed on.

However, the US Environmental Protection Agency's notification that it issued to VW has given the industry some indication of how it was installed, and how it works.

What do we know?

The EPA reported that "VW manufactured and installed software in the electronic control module (ECM) of these vehicles that sensed when the vehicle was being tested for compliance with EPA emission standards", which means that there is a clever algorithm contained in the engine CPU software that detects when the vehicle is undergoing emissions testing.

The algorithm sounds particularly intuitive, but although its complex, it should be relatively straightforward. Contrary to the name suggests, it's not an actual physical device, but rather some code written into the software in the engine ECM that controls various factors.

We can speculate that the software records the engine speed, barometic pressure, tyre rotation and other various inputs, and if this matches official emission testing conditions, then the Defeat Device will probably be started. This will 'tune' the engine to change the way it behaves under the conditions, lowering the amount of emissions produced as a result.

Because the software is located behind a 'firewall' underneath the dashboard, it is difficult - if not impossible - to access by anyone other than those working for the company themselves.

How does European emissions testing work?

Vehicles undertaking the Euro emissions test undergo a range of tests in laboratory conditions. Click on a photo below to find out more about the test, and how it can be manipulated.

Tyres Exhaust Fan

The test process

Click on each of the images to find out more about the European emissions testing, and how technicians attempt to replicate on-road driving conditions.

Rear Lights Temperature Air Conditioning

What else?

Urea. Remember that word, as you'll be hearing it a lot over the coming weeks and months. Urea is a fluid that is used to reduce the amount of nitrogen oxide (the bad stuff) that is pumped out of the exhaust. The more urea that is pumped into the exhaust system, the more NO2 is reduced.

However, urea is used quickly by the exhaust system, and it runs out quickly, so it isn't used under normal road driving conditions (i.e. by anyone other than an emissions testing lab).

An urea injection system is often expensive, and can't be justified for cars at the lower end of the price scale, so VW decided to beat the system by creating the Defeat Device piece of software. When the algorithm detects that the vehicle is being driven under laboratory test conditions, the ECM will make changes to the engine running state to reduce emissions and meet official efficiency levels.

As a result, engine power levels and efficiency are reduced, which is bad news for the owner-driver, but great news for the emissions testing team because it ensures it passes the required levels.

See also