Dieselgate: the less visible side of the scandal

The emissions scandal that became public in 2015 around Volkswagen AG and its diesel vehicles created enormous public attention. Some owners worried about the resale value of their cars, others were angry that the emissions figures declared by the manufacturer were very different from real-world operation, while many simply ignored the whole story. The situation soon became known worldwide as Dieselgate.

The Dieselgate scandal mainly affected many diesel engines produced between 2008 and 2015: 1.6 TDI, 2.0 TDI, some 1.2 TDI engines and also certain 3.0 TDI versions, although the latter were often mentioned less openly in public communication. In many cases, emissions values — specifically nitrogen oxide (NOx) emissions — were partly manipulated during official emissions testing.

The wider public was mostly presented with information about environmental pollution from Volkswagen, Audi, Škoda and Seat engines. Much less attention was paid to the fact that similar software strategies or emissions-related investigations also appeared around some Mercedes-Benz, BMW, PSA Group, General Motors / Opel and Fiat diesel vehicles. So what happened next?

In Europe, many affected vehicles received software updates intended to reduce NOx emissions substantially. The smaller 1.6 TDI engines also received a small plastic insert in the air intake system, usually referred to as an airflow straightener. This part slightly changes the airflow characteristics entering the engine. The question is: what was the cost of this “fix”?

1.6 TDI plastic airflow straightener used during the Dieselgate update campaign

European customers were treated rather differently from customers in the United States. Due to a different legal framework and different vehicle compliance requirements, Volkswagen AG had to pay significant compensation to US buyers and repurchase a large number of affected vehicles, reportedly more than 300,000 units. In Europe, the approach was different: instead of broad compensation, most customers received software updates and, in the case of some 1.6 TDI engines, the plastic airflow insert.

In simple terms: after Dieselgate, many US customers received compensation or buyback options, while European owners mostly received software updates and hardware inserts. The consequences of these updates are the subject of this article.

Dieselgate engine control software updates

Volkswagen AG, looking for a practical way out of the situation, had to solve a difficult task: reduce emissions from already-produced diesel vehicles sold in Europe. More specifically, instead of paying compensation to all owners, the manufacturer had to reduce nitrogen oxide (NOx) emissions through engine control software updates.

This is how the so-called Dieselgate software updates appeared. In many cases, they really did reduce NOx concentration in exhaust gases. But again, the important question is: at what cost?

Engine torque had to be reduced across a wide RPM range in many software versions, which noticeably reduced vehicle performance
Fuel consumption increased, statistically often by around 5–12%
CO2 emissions increased proportionally with fuel consumption
EGR valve service life became noticeably shorter
DPF service life became shorter due to much more frequent regeneration cycles
Injectors and high-pressure fuel pumps experienced harsher operating conditions, often together with a sharper and louder engine sound under load or at higher RPM

Frequent DPF regeneration increases fuel consumption and shortens the useful life of the filter. One common symptom is the engine cooling fan continuing to run after the engine has been switched off, even when the outside temperature is not high. This often indicates that a DPF regeneration process was interrupted.

A more frequently opened EGR valve means more exhaust gas — and therefore more soot — being fed back into the intake system and engine. This increases contamination inside the intake system and reduces the service life of the EGR valve itself.

What changed after the updates?

To meet the required nitrogen oxide emission values, fuel quantity and combustion strategy had to be changed. Energy does not appear from nowhere: when fuel quantity and combustion behaviour are altered, available torque is reduced. Peak torque may drop by 10–20%, but the more serious issue is the loss in the important diesel working range of around 1500–2300 rpm. In some 2.0 TDI cases, torque in this range may be reduced dramatically — for example, from around 380 Nm before the update to around 220 Nm after it, according to data observed on VW Passat 2.0 TDI 130 kW vehicles.
Fuel consumption after Dieselgate software updates often increases by around 6–13%, depending on the exact engine and software version. This is mainly related to more frequent EGR operation, changes in injection timing and additional fuel used for DPF regeneration. The result is less torque and higher fuel consumption.
In addition to more frequent EGR operation, DPF regeneration happens much more often. Extra fuel is used for this process. The exhaust system and the turbocharger located near the DPF are exposed to higher thermal load more frequently, which does not help their service life. One typical Dieselgate symptom is the radiator fan continuing to run for several minutes after the car is switched off — an attempt to control temperature after frequent DPF regeneration.
In many engines that received Dieselgate software updates, fuel pressure parameters were also changed. In some versions these changes are aggressive enough that injector “knocking” can be heard at low RPM. It may sound as if the injectors are worn and need replacement. We have seen many cases where 1.6 TDI and 2.0 TDI engines started working louder immediately after Volkswagen, Audi, Škoda or Seat dealer software updates. In some cases, workshops even suggested replacing injectors costing several hundred euros each. After restoring non-Dieselgate engine control software, the symptoms often disappeared.

The conclusion is simple: Dieselgate software updates may reduce NOx emissions, but they can also harm engine behavior, vehicle dynamics, fuel consumption and the service life of related components. Unfortunately, many vehicle owners do not notice or understand these technical consequences immediately. The situation was convenient for the manufacturer, but not necessarily for the vehicle owner or their wallet.

We can detect Dieselgate engine software quickly and clearly. When performing engine programming work, we restore a more engine-friendly software version where technically appropriate. As a separate service, this is usually not expensive and depends on the engine type and how deeply the updated software strategy is hidden.

300000 Dieselgate affected cars bought back from US customers