Emission Tampering

W. Addy Majewski

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Abstract: Tampering involves changes in hardware or software that may impair the performance of the vehicle’s emission control system. In modern engines, tampering comprises not only changes to emission system hardware, but also modified engine management software. Electronic defeat devices include ‘performance tuners’ that recalibrate the engine to improve performance or fuel economy, and ‘delete tuners’ that overwrite the OBD system to allow the removal or deactivation of SCR catalysts, particulate filters, and other emission system components.


Terms & Definitions

The term tampering refers to changes in hardware or software that may impair the performance of the vehicle’s emission control system or—in a more general scope—its environmental protection systems. In US legislation, tampering is described as “to remove or render inoperative any device or element of design installed on or in a motor vehicle or motor vehicle engine in compliance with regulations[42 USC 7522]. European type approval regulations define tampering as the “inactivation, adjustment or modification of the vehicle emissions control or propulsion system, including any software or other logical control elements of those systems, that has the effect, whether intended or not, of worsening the emissions performance of the vehicle[3493].

Using simpler language, emission tampering could be described as any action that takes an emission certified engine or vehicle out of the certified state. The hardware components and/or software used to tamper an engine or vehicle are known as emission defeat devices, after a legal term used by emission regulations in the United States and other countries. Colloquially, tampering is also referred to as deleting an emission control system or its components.

In older, mechanically controlled engines, tampering typically involved changes to various components in the fuel injection system and EGR. In modern electronic engines, tampering involves not only changes to emission system hardware, but also—and foremost—modified engine management software. The tampering software files, known as “tunes”, are used in tandem with electronic hardware devices, known as “tuners”, to interface with and reprogram the vehicle’s original software. In diesel engines, these devices are also known as “diesel chips”. An example tuner device is shown in Figure 1.

Figure 1. Superchips F5 GM Flashpaq performance programmer

A handheld tuner applicable to a range of Chevy and GMC pickup trucks with gasoline and Duramax diesel engines. Superchips part number 2845.

(Source: Superchips, 2021)

Tampering can have a very significant effect on emissions, particularly when it involves the removal or deactivation of aftertreatment devices. In modern engines, this is facilitated by “delete tunes”, an important class of aftermarket defeat devices that reprogram engine functions and override the OBD system so the tampered vehicle operates without any diagnostic trouble codes, even though the vehicle’s aftertreatment systems may be removed.

‘Tunes’ and ‘tuners’ that reprogram the vehicle software or calibration are commonly used for tampering in the North American market. In the European market, electronic ‘emulators’ that manipulate various messages send and received by the engine control module are often used to disable emission system components. For instance, an ‘SCR emulator’ can be used to disable the SCR system and to operate the vehicle without urea, while an ‘EGR emulator’ allows to electronically disable EGR flow, without physically blocking off the EGR pipe.

How Widespread Is Tampering?

People can tamper vehicles and engines for a number of reasons. In light-duty vehicles, common reasons for tampering include increased performance (power and torque) or customization of the vehicle. As vehicles age, tampering can provide a cost-effective repair option—various forms of tampering or the use of sub-standard aftermarket parts is an attractive alternative to the otherwise costly repairs of the emission system.

In commercial vehicles, tampering is commonly driven by a desire to reduce costs, such as by reducing fuel consumption and by avoiding the cost and time to maintain emission aftertreatment devices. Examples include DPF removal to improve fuel economy and avoid the need to service the filter, or deactivation of SCR systems to avoid the need to replenish urea solutions (AdBlue, DEF).

In same cases, tampering may be necessary to enable travel into areas of different fuel quality and availability of urea. For instance, some European truck operators feel they need to “delete” or disable the DPF/SCR components when traveling to countries outside of the EU, where ultra-low sulfur diesel fuel and urea solutions may not be readily available.

Under most jurisdictions, emission tampering is illegal. Various regulatory prohibitions of tampering may be applicable to manufacturers, vehicle dealers, repair facilities, technicians, fleet operators, vehicle owners, and the general public. In spite of statutory prohibitions, tampering remains widespread worldwide. In some localities, anti-tampering regulations are inadequate and/or are not enforced. Even in jurisdictions with otherwise strong record of enforcement of emission regulations, tampering remains a common practice.

The US EPA believes tampering occurs in most vehicle categories, including commercial trucks, passenger vehicles, pickup trucks, motorcycles, forestry equipment and agricultural equipment [5036]. Aftermarket emission defeat devices are commonly available from many, usually smaller size, suppliers and are widely advertised on the internet. However, emission tampering remains elusive to quantify, and estimates on the scale of the problem or its emission effects can vary considerably.

In the United States, a 1978 survey by the EPA found that 19% of model year 1973-1978 cars were tampered, and an additional 48% of cars showed at least one “arguably tampered” item [5037]. Fast-forward through four decades to 2020, and another EPA study found that approximately 15% of the national population of diesel pickup trucks that were originally certified with emission aftertreatment were tampered [5036]. The report focused on emission aftertreatment delete kits (other types of tampering were excluded) installed in 2009-2020 Class 2b and 3 heavy pickup trucks, such as the Chevrolet Silverado and Dodge Ram 2500. According to other estimates, some 30-60% of newer model year light-duty diesel pick-up trucks in the USA may have been tampered with [1335]. Data on tampering in other vehicle categories such as commercial trucks or nonroad equipment is even more scarce. Some estimates put the rate of tampering with engine electronics in heavy-duty trucks at 5-15% [1457].

In the European Union, various pilot studies on SCR tampering in heavy-duty trucks produced estimates ranging from 1-2% in Sweden to some 20% in Germany and Denmark [5038][5034]. An enforcement campaign by the Spanish Guardia Civil found, using remote emission measurements, that about 20% of Euro V trucks produced excessive NOx emissions [5035]. The offending vehicles were then pulled over for an inspection. It was found that 47% of the high-emitters were tampered, which would translate to an overall SCR tampering rate of around 10%.

According to estimates, 5-10% of the diesel passenger car fleet in Europe is deemed to have either defective or missing DPF systems. Considering passenger car DPF manipulations and defects, approximately 10% of the fleet is responsible for 90% of the total emissions [5038].

Prevention of Tampering

A number of approaches and technologies can be used to make tampering more difficult. These include a range of vehicle design and approval features such as marking of OEM and replacement components with mandatory approval marks, better access to vehicle systems (visual and mechanical access, sensor readings, actuators operation), self-diagnostic software features, and an anti-tuning control unit [5032].

Software features can be designed to detect tampering, and used in addition to visual checks. For instance, the vehicle calibration identification (Cal-ID) and the calibration verification number (CVN) can be a good and tamper-proof indication that changes have been made to the vehicle software or calibration. The Cal-ID is the identifier of the vehicle software assigned by the vehicle manufacturer, while the CVN is a unique code calculated based on the Cal-ID, such as using checksum. Whenever vehicle’s software or calibration is modified, a new CVN is automatically generated that will differ from the one originally associated with the Cal-ID.

Cal-ID/CVN requirements are included in most OBD regulations worldwide, but the effectiveness of this approach depends on the quality of specifications. California OBD regulations are very strict on the details in their Cal-ID/CVN implementation. As a result, California Cal-ID/CVN is considered highly challenging to manipulate, while some Cal-ID/CVN implementations in other jurisdictions are easily exploited.

The EU-funded DIAS project has been formed to harden vehicle emission control systems against tampering. The objective of the project is to develop techniques to detect and prevent changes to the vehicle’s emission hardware or software. In the case of detection, the tampering information would be used to introduce countermeasures, such as the activation of a driver inducement system [5033].

In addition to hardening the vehicle emission control system, a number of anti-tampering approaches are possible beyond vehicle approval:


We appreciate the help of Marcel Romijn of Roben Automotive, who provided background technical information and valuable feedback on this article.