This Is How Volkswagen's Diesel Emissions Cheat Works, According to ECU Hacker (Video)

Volkswagen’s emissions cheating program closely follows a set of parameters that are very similar to those defined by the New European Driving Cycle (NEDC), an engineer said this week.

The cheat exists in the ECU’s “main mode,” said Felix Domke, and triggers a normal dosage of urea and other exhaust controls to bring NOx emissions to within acceptable levels.

Domke presented his findings of an unpacked Volkswagen ECU to the 32nd Chaos Communication Congress in Germany.

His findings are mostly in line with what the automaker has already admitted: its 11 million cars worldwide cheated emissions tests by using two different modes for operation, and that its cars could pollute up to 40 times the legal limit of nitrogen oxides when running normally.

But Domke, who said he owns a Volkswagen Sharan equipped with a 2-liter diesel engine, said his own observations showed a severe change in the ECU’s behavior when it exceeded the bounds of what it considered was an emissions test — more than what’s been reported so far.

Domke said he purchased a Volkswagen ECU online and extracted its millions of lines of code. The VW ECU’s behavior is mostly governed by parameters defined outside of its code — not constants that would be hard-coded into the programming — embedded within the computer’s hardware.

He said the car’s main modes for exhaust management were a “normal mode” and an “alternative mode,” the latter of which mostly dominated the car’s behavior. In his own driving, after observing the state of the car, Domke said he found the car ran in a “cold start” cycle for roughly 20 percent of the time and on its “alternative mode” for nearly 80 percent of his driving. Only a small fraction of his normal, everyday driving was in “normal mode.” During “normal mode,” the selective catalytic reduction system used by Volkswagen would consume significantly more diesel emissions fluid than in “alternative” mode. Domke said that finding was supported by additional observations: his van used far less urea than he anticipated.

Domke said he graphed the European emissions testing cycle and overlaid those results with the upper and lower limits of the ECU’s “normal mode” and discovered that the mode aligned perfectly with the limits.

He didn’t test differences in engine performance, nor could he say whether the cheat applied to cars in other countries. But Domke pointed to a parameter in the engine’s code that seemingly always initiated its “alternative” exhaust program: the outside temperature would only need to be suitable for life to exist — above -6,357.9 degrees Fahrenheit (-3,550 degrees Celsius).

Only after a fairly specific set of conditions were met: atmospheric pressure, temperature, speed and distance, which coincide with the NEDC testing parameters, would the car begin its “normal” cycle.

Domke presented his work with Daniel Lange, a former BMW engineer who said the likelihood that the ECU was developed by a “small group” of Volkswagen engineers is hard to believe. Lange said roughly 1,000 hard disks were confiscated from 380 employees, which is hardly a small group.

Also, Lange said the paper trail for documenting changes to an engine’s ECU is prolific — there are too many laws that govern how cars are controlled and automakers fastidiously document those changes for legal reasons.

The presentation is just over 1 hour long. If you want to get to the meaty stuff right away — like how the “defeat device” worked — skip ahead to around 51 minutes in. Otherwise, grab some popcorn.