Part 6/9:

In response to these challenges, manufacturers resorted to compromises that undermined the fundamental efficiency of diesel engines. The introduction of diesel particulate filters (DPFs) and various emissions control technologies, while theoretically solutions, resulted in higher vehicle maintenance costs and complex operational requirements for owners. The discrepancies between emissions testing in controlled environments and real-world conditions—exacerbated by outdated testing methodologies—hid the growing problems associated with diesel.