An entire marketplace exists on the Internet for tuners, devices that help drivers crank up the power on vehicles and then hide the evidence. We visit a local diesel shop to see how it works.

The nefarious workaround — and the crux of the Dieselgate scandal — was for engineers to reprogram the vehicle's Electronic Control Unit (ECU).

Lawmakers want to know more about Volkswagen's massive cheat — how the automaker used software to crank up the power on a vehicle, and then hide the fact.… ...