Audi Q8 vs. Mercedes-Benz GLS: Complete comparison 2026

Audi Q8 represents the brand's flagship offering in the luxury SUV coupé segment, where it confidently combines sporting dynamics with first-class technology and an attractive design. Standing against it is the Mercedes-Benz GLS, a model formerly known as the GL-Class, which serves as the proverbial S-Class among giant SUVs and places extraordinary emphasis on absolute comfort and maximum interior space for seven passengers. Let's take a detailed look at how these two prestigious representatives of the premium class stand in a head-to-head battle and which of them will better suit your daily and driving needs.

Exterior Dimensions and Proportions

Although the Audi Q8 and Mercedes-Benz GLS belong to the prestigious luxury SUV segment, their exterior proportions reflect completely different approaches by the two automakers to design and interior space. If we focus on used car market models roughly four years old (the 4M generation for Audi and 167 for Mercedes from 2020–2022), it is clear at first glance that while Audi bets on a dynamic silhouette evoking a sports coupe, Mercedes-Benz offers a more classic, boxy concept of a full-sized family cruiser. In terms of overall length, the Mercedes-Benz GLS dominates with an impressive 5207 mm, meaning it is exactly 221 mm longer than the Audi Q8, which measures 4986 mm in length. A similar difference exists in the wheelbase, where Mercedes offers 3135 mm compared to 2995 mm for Audi. This significant difference in overall length and the 140 mm longer wheelbase clearly earmark the Mercedes-Benz for larger families who care about maximum space and the option of a third row of seats, while the more compact Audi Q8 will be appreciated by drivers looking for a compromise between luxury and at least partially acceptable maneuverability when parking in city centers and underground garages.

However, a very interesting turn occurs when we compare both SUVs in terms of width. Although the Audi Q8 is a noticeably smaller car in the longitudinal direction, with its width of 1995 mm, it paradoxically surpasses the mammoth Mercedes-Benz GLS (1956 mm) by a significant 39 mm. This contrast is further enhanced by the vast difference in body height. The Mercedes-Benz towers to a majestic height of 1823 mm, while the athletically cut Audi measures only 1705 mm. This represents a huge difference of 118 mm in favor of the Stuttgart representative. The wide track in combination with the significantly lowered roofline gives the Audi a much more aggressive and road-hugging stance. While the lower and wider build of the Audi Q8 contributes to significantly higher stability in corners and gives the driver more sporty confidence behind the wheel, the tall and narrower body of the Mercedes guarantees unsurpassed headroom for all passengers and a dominant view of the road, sought after by lovers of traditional large SUVs.

When choosing a luxury SUV, trunk capacity often plays a key role, especially if you plan to use the vehicle as your primary family car. The difference between the Audi Q8 (4M generation) and the Mercedes-Benz GLS (167 generation), which dominate the market for roughly four-year-old used cars, is quite fundamental in this regard. Both cars approach the concept of interior space differently – while the Mercedes-Benz GLS is a massive family cruiser offering up to a seven-seat layout, the Audi Q8 bets on a more dynamic silhouette and an exclusively five-seat interior, which directly affects both the available and stated trunk capacity.

The Audi Q8 scores with excellent accessibility and offers a very generous 605 liters in its basic configuration, which is plenty of space for weekend shopping or longer vacations. After folding the rear seats, the total capacity increases to an impressive 1,755 liters. However, if you are considering a more eco-friendly option, it's good to know that the popular plug-in hybrid versions (such as the Q8 55 TFSI e) have a slightly reduced trunk space of 505 liters due to the traction battery being placed under the floor. This still represents a solid value, but this difference can play a role when packing bulkier items.

In contrast, the Mercedes-Benz GLS is literally the king of space. While the tables show a basic value of 355 liters (where the Audi Q8 has a technical lead of 250 liters), this only applies when all seats in all three rows are upright. The real advantage of this model fully manifests as soon as you start folding the rear rows into the floor. In a two-seat configuration, the GLS provides a gargantuan 2,400 liters of maximum volume, outclassing the Audi Q8 by a staggering 645 liters. In practice, this means huge space for several extra suitcases, trouble-free transport of bulky sports equipment, or even the possibility of transporting smaller furniture.

Trunk Capacity Comparison

When choosing a large premium SUV from the used car market, towing capacity often plays a key role. The weight of the trailer that the car can safely pull determines its practicality for an active lifestyle – whether it's towing a heavy caravan, a horse trailer, or a boat. Here, it turns out that between roughly four-year-old Audi Q8 (generation 4M) and Mercedes-Benz GLS (generation 167) models, there are quite fundamental differences that could significantly influence your decision.

While the Mercedes-Benz GLS, as a massive full-size SUV, offers a standard and maximum braked trailer capacity of a full 3,500 kg in all common engine versions (GLS 450 and diesel GLS 450 d), the situation with the Audi Q8 is a bit more varied. Common combustion variants of the Audi Q8, such as the popular 45 TDI and 50 TDI diesel engines or the 55 TFSI petrol from 2020–2022, can standardly handle a braked trailer weighing 2,800 kg (with some older petrol versions even only 2,700 kg). Both manufacturers then consistently offer a capacity of 750 kg for an unbraked trailer, which is the maximum set by European legislation.

The differences deepen if you focus on alternative powertrains. An interesting exception in the Audi range from those years (2020–2022) is the top-of-the-line plug-in hybrid model Q8 60 TFSI e, whose design allows for towing a maximum of 3,500 kg, matching the GLS. However, if you were considering the fully electric Q8 e-tron (generation GE), expect a significantly reduced capacity – this electric car can only tow a trailer up to 1,800 kg.

In practice, this difference means that the Audi Q8's towing power at 2.8 tonnes is fully sufficient for a standard family caravan or a medium-sized boat for a longer holiday, but it may reach its limits with professional and extremely heavy trailers. In contrast, with the 3.5-tonne capacity of the Mercedes-Benz GLS, you get maximum versatility without having to worry about which engine you actually have under the hood.

Conclusion: If you plan to use the car as the ultimate workhorse for the heaviest loads, the Mercedes-Benz GLS represents a safe bet. With the Audi Q8, you either have to settle for a slightly lower (though still very good) towing capacity, or you must specifically look for the particular high-performance Q8 60 TFSI e plug-in hybrid from the specified production years.

When choosing a luxury SUV, the range of engine options plays a crucial role, as it affects not only dynamics and fuel consumption but also the overall character of the vehicle. Both the Audi Q8 and Mercedes-Benz GLS rely exclusively on powerful six-cylinder units with all-wheel drive, yet their approach to electrification and performance differs slightly. While the Audi Q8 offers a wide spectrum of classic TDI diesel engines and advanced plug-in hybrid (TFSI e) variants with the possibility of purely electric range, the Mercedes-Benz GLS focuses its internal combustion versions on velvety smooth inline-six engines supported exclusively by 48V mild-hybrid EQ Boost technology. For used car buyers looking at vehicles approximately four years old, this means a clear choice: the sportier-styled Audi can be very efficient with regular charging from the grid, while the majestic Mercedes-Benz scores with the mammoth torque of its mild-hybrids, which excel during long highway journeys and when towing heavy trailers.

Audi Q8 Engine Options

The engine range for the Audi Q8 (generation 4M) covers a wide spectrum of needs, with all standard versions relying on a 3.0-liter V6 and the proven eight-speed Tiptronic automatic transmission paired with quattro all-wheel drive. The base of the diesel range is the 45 TDI version with 170 kW, however, a much more sought-after choice on the used car market is the more powerful 50 TDI with 210 kW and a solid 600 Nm of torque. Traditional petrol engines are represented by the standard 55 TFSI (250 kW). For drivers who want to combine high performance with the possibility of daily emission-free commuting, Audi offers the 55 TFSI e plug-in hybrid models and the flagship 60 TFSI e, boasting a powerful system output of 340 kW. The electrified TFSI e variants became a permanent part of the range between 2020 and 2025, although for used units, it is necessary to keep in mind the higher curb weight due to the built-in batteries.

Mercedes-Benz GLS Engine Options

The Mercedes-Benz GLS (generation 167) takes a more majestic approach to propulsion, hiding refined 3.0-liter inline-six engines under the hood, which are always paired with the smooth-shifting 9G-TRONIC nine-speed automatic transmission and the 4MATIC all-wheel drive system. A specific feature of the GLS engine range is the widespread implementation of mild-hybrid technology, which effectively aids efficiency and the smoothness of starts, and allows for "coasting" with the internal combustion engine switched off. The petrol GLS 450 version offers a generous 270 kW (increased to 286 kW in newer model years). Although older diesel versions like the 350 d or 400 d were available on the market in the first years of production, today's selection of younger used cars and newer models focuses on more advanced units. A major innovation from 2023 is the GLS 450 d model, which confidently replaced the previous diesels with 270 kW and a mammoth 750 Nm of torque. These mild-hybrid six-cylinder engines represent an absolutely ideal compromise between dazzling dynamics and reasonable running costs.

Choosing the right engine is crucial for long-term satisfaction, and both premium SUVs require a powertrain adequate for their dimensions. While the Audi Q8 bets on a sharper design and is tuned with a greater emphasis on the driving experience, the massive Mercedes-Benz GLS functions as a luxury family cruiser that must effortlessly move a weight approaching 2.5 tons. An interesting point from a development perspective is the different approach of the manufacturers to six-cylinder engines – Audi relies on the traditional V-shaped (V6) layout for its core TDI units, while Mercedes-Benz returned to masterfully balanced inline-sixes (R6) for the X167 generation. Our recommendations for the market of roughly four-year-old used cars (or a generation younger) are based on performance, real-world fuel consumption, mechanical durability, and long-term owner feedback.

For the Audi Q8, we recommend: 50 TDI (210 kW)

In the vast competition of premium engines, the 3.0 V6 TDI diesel (labeled as 50 TDI) represents the best compromise between dynamics, reliability, and everyday usability. As shown in the table with available years (AVAILABLE_YEARS), the early iteration of the 50 TDI version for the market of roughly four-year-old used cars from 2020–2022 is no longer produced in its original form today, making it an exceptionally interesting and sought-after choice on the secondary market.

• Why it's the best choice: The engine offers a massive 600 Nm of torque, which handles the heavy SUV coupe with ease. At the same time, it pleases with excellent real-world fuel consumption oscillating around 8 to 9 l/100 km, which is an excellent value considering the size of the vehicle and all-wheel drive.
• Technical advantages: The engine block itself (EA897evo3 generation) is mechanically very robust. It pairs perfectly with the traditional eight-speed Tiptronic automatic transmission (torque converter from ZF), which guarantees an exceptionally smooth highway ride and keeps the RPMs very low at higher speeds.
• Risks and solutions: The most well-known user weakness is a slight delay in throttle response when starting from a standstill, caused by conservative emission mapping of the transmission software. Furthermore, if the vehicle served as a means for short shopping trips around town, there is a risk of gradual clogging of the diesel particulate filter (DPF) and carbon buildup in the intake manifolds. Crucial advice: When buying, require a check of the DPF fill level via diagnostics, avoid neglected units, and after purchase, regularly take longer, brisker trips to allow for trouble-free filter regeneration.
• Who it's for: A perfect choice for highway mile-munchers, dynamically-minded travelers, and drivers who require confident power complemented by a huge range on a single tank.

For the Mercedes-Benz GLS, we recommend: GLS 450 d (270 kW)

For the majestic seven-seater SUV, a powerful diesel six-cylinder is the only truly rational choice. If you are looking for a classic roughly four-year-old used car, you will likely come across older versions labeled as 350 d or 400 d. However, as you can notice in the availability data (AVAILABLE_YEARS), these older engines are no longer recorded in the databases of newer generations and are not available. Therefore, for maximum reliability, we recommend focusing on slightly younger used cars with the modernized and extremely successful GLS 450 d unit (available from late 2023), which is their direct successor.

• Why it's the best choice: The 270 kW (367 hp) output from the OM 656 M inline-six offers stunning and refined power. While gasoline engines (such as the GLS 450) offer similar performance, in such a colossal car fully loaded with passengers, the diesel pays off with much better low-end pull and significantly friendlier operating costs.
• Technical advantages: The integration of a 48V electrical system with an integrated starter-generator (ISG) ensures that starts are completely imperceptible and the electric motor effectively smooths out any turbo lag or throttle delay. The nine-speed 9G-TRONIC automatic transmission is tuned to perfection with this unit and shifts practically imperceptibly.
• Risks and solutions: A luxury and heavy SUV hides many complex mechanical solutions. The emission system (multiple AdBlue fluid injection) is sensitive to fuel degradation and deposits from cold starts. Additionally, the massive curb weight takes an unforgiving toll on the consumables of the air suspension (air bellows, compressor). Recommendation: Choose exclusively cars from the first owner with a flawlessly documented service history. Avoid units used only for school runs in city centers, as their exhaust gas treatment system and chassis are under the highest load.
• Who it's for: Built for maximum comfort and travel across all of Europe. An ideal choice for large families, lovers of quiet, supple suspension at the "S-Class" level, and for drivers who need to tow boats or horse trailers with absolute confidence.

Paper fuel consumption values stated by manufacturers according to measurement standards often differ significantly from everyday reality in practice, which is doubly true for large and heavy SUVs with a weight reliably exceeding two tons. To obtain an objective and as accurate as possible picture of the actual operating costs of approximately four-year-old used cars, it is therefore ideal to look at long-term user statistics. Data from the popular independent platform Spritmonitor.de, where thousands of drivers enter real values from every refueling, provide us with a clear idea of the appetite with which individual engines of the Audi Q8 (4M generation) and Mercedes-Benz GLS (167 generation) operate in the real world.

A detailed look at the averaged data reveals a completely clear trend: despite today's massive onset of electrification, modern diesel six-cylinders remain an absolutely unsurpassed benchmark of efficiency for giant premium SUVs. The popular Audi Q8 50 TDI diesel or the majestic Mercedes-Benz GLS 450 d can, despite their gigantic dimensions and standard all-wheel drive, drive with a real average consumption of around nine liters per hundred kilometers, which is a fantastic result considering their power and frontal resistance. Large purely gasoline engines (Q8 55 TFSI and GLS 450) score with drivers for their top-notch refinement, but in practice, they regularly ask for about 2.5 to 3 liters more fuel. Plug-in hybrids, such as the Audi Q8 55 TFSI e, are a completely specific category. Their standardized "paper" consumption of around two liters is illusory in normal mode without daily battery charging. In long-term combined operation, their real average most often settles around 6.5 l/100 km.

For the average user and those interested in a luxury family SUV, these values mean a relatively clear layout of priorities. For drivers who use the vehicles for long highway commutes or regularly swallow hundreds of kilometers across Europe, classic diesel power makes the most sense both economically and for the user. It offers not only reasonable fuel bills but, above all, a confident range approaching a thousand kilometers on a single tank. Gasoline variants, on the other hand, are more suitable for buyers with lower annual mileage who are happy to pay extra for absolute silence and do not mind more frequent visits to gas stations. The Plug-in hybrid Audi Q8 is then an ideal choice almost exclusively for that circle of owners who have the possibility of trouble-free overnight charging at home or at work and whose daily city commuting is fully covered by the purely electric range.

Fuel consumption may not be the only and absolutely most important parameter when buying a premium used car with a price tag exceeding €41,000, but it plays a very significant role in total operating costs at higher mileages. Summarizing the real data above, diesel variants for both cars remain the most rational possible choice in terms of everyday economy, robustness, and travel comfort. Whether you reach for the sportier-tuned Audi Q8 or prefer the maximally spacious Mercedes GLS, diesel under the hood will guarantee you a reliable and, by the standards of the class, surprisingly frugal companion.

Used Car Price Comparison: Audi Q8 vs. Mercedes-Benz GLS

The luxury used SUV market offers very interesting opportunities after approximately four years of operation. In this comparison, we focus on models from 2021 and 2022, which represent the ideal age for buying a used car. In the case of the Audi Q8, these are first-generation vehicles (code name 4M) that defined the category of sportily styled SUV coupés with the four rings on the grille. During the same period, the Mercedes-Benz GLS falls into its third generation (X167), which is considered the proverbial "S-Class among SUVs" and, unlike the Audi, offers massive space for up to seven passengers.

Both cars started at very high purchase prices when new. While they experience a significant drop in value after a few years, their price dynamics on the used market differ slightly due to their different character and target audience.

Estimated Price Overview (2021–2022 models)

The table below shows the approximate price range for four-year-old models with a verifiable history and clear origin on the European market.

Audi Q8: Sporty Elegance with a More Affordable Price Tag

Used Audi Q8s from 2021 and 2022 are very popular choices for drivers looking for a prestigious and dynamic design backed by cutting-edge technology.

• Dominance of diesel engines: The vast majority of listings consist of the 50 TDI diesel versions (a three-liter V6 with 210 kW). These models with higher mileage can be purchased just below the €41,000 mark.
• Plug-in hybrids and petrol: Models labeled 55 TFSI e (plug-in hybrid) or pure petrol 55 TFSI are rarer on the used market, and their prices usually stay about 10 to 15% higher than comparable diesels.
• Impact of equipment on price: A key element for maintaining value on the used market is the S line sport package, which gives the car a significantly more aggressive look. Units in the base visual trim tend to be noticeably cheaper but may be harder to resell later.

Mercedes-Benz GLS: The Seven-Seater Giant Holds Its Value

The Mercedes-Benz GLS is a physically larger vehicle that has targeted a different – more family-oriented and maximum-comfort-oriented – clientele from the start. This is positively reflected in its residual value.

• Powerful and efficient diesels: Similar to Audi, diesel six-cylinders dominate the secondary market for Mercedes, namely the popular GLS 350 d and the more powerful GLS 400 d. They represent the best compromise between smooth pulling power for a heavy SUV and real-world fuel consumption.
• Premium for family space: The GLS features three full rows of seats, making it a highly sought-after commodity for larger families. There is stable demand for such vehicles on the market, so used units hold their price better and do not depreciate as quickly as the Q8.
• Extreme top of the range: While Audi ends with the extremely fast RSQ8 model, Mercedes can go even further. It offers not only the sharp AMG 63 variant but also ultra-luxury Maybach versions. For these, prices can easily exceed the €144,000 mark even after four years.

Depreciation and Market Outlook

Luxury vehicles in this weight and price category experience the steepest drop in value during the first three years of operation. When buying a four-year-old car, the buyer pays only about 50% of the original list price of a new vehicle.

The Audi Q8 loses value slightly faster in percentage terms, partly due to strong competition in the prestigious large SUV coupé segment (where it competes fiercely with the likes of the BMW X6 or Mercedes-Benz GLE Coupé). In contrast, the GLS benefits from its relative exclusivity. There are fewer luxury family cruisers of this size on the European market (practically the only direct rival is the BMW X7), which naturally keeps used GLS prices at a higher level.

When choosing a used premium SUV, safety is often one of the main criteria. In this class, a five-star Euro NCAP rating is common, but it is crucial to put these results into the correct context and take the year of testing into account. Euro NCAP crash test methodology and protocols are constantly evolving and becoming more stringent. They include, for example, new frontal impact simulations, more advanced cyclist detection, or emergency scenarios at intersections. For this reason, percentage ratings from different years cannot be directly compared, as an older five-star result may no longer meet today's stricter safety standards.

Audi Q8 underwent Euro NCAP crash tests in 2019, receiving the maximum five-star rating. Given this year, the certification is older by current standards and was conducted according to the regulations of the time; however, the car showed above-average structural strength and a high level of protection. The model achieved a score of 93 % for adult occupant protection, 87 % for child occupant protection, 71 % for vulnerable road user protection (pedestrians and cyclists), and 73 % for safety assist systems. The results show that while occupant protection is top-notch, there is already a gap between its active assistants and the most modern requirements of today.

In the case of the Mercedes-Benz GLS (current generation X167), official data is missing because Euro NCAP did not test this model directly. This is a relatively common practice for very expensive and heavy luxury SUVs with lower sales in Europe. However, conclusions can be drawn from the results of the technically related and slightly smaller Mercedes-Benz GLE, which also received a full five stars in the same year. Since there is no relevant crash test data specifically for the GLS model, we are leaving its values in the table blank.

In conclusion, both vehicles offer superior protection due to their massive construction, advanced crumple zones, and a wealth of active safety features. Although the Audi Q8 has its safety level formally confirmed by an older test and the Mercedes GLS lacks this confirmation, both models represent an exceptionally safe choice on the four-year-old used car market.

In addition to the rich standard equipment, each of the models offers several unique features that clearly demonstrate their different approaches to luxury and overall added value.

Audi Q8: Technological avant-garde and sporty style

The brand's flagship SUV-coupe focuses primarily on combining dynamic design with advanced dashboard digitalization.

• Infotainment and digitalization: At the heart of the interior is the MMI touch response system, which relies on two large stacked touchscreens. It completely replaces physical buttons while providing haptic and acoustic feedback for more confident control while driving. This is complemented by the top-tier Audi virtual cockpit digital instrument cluster.
• Cleverly designed: The car's exceptional appearance is highlighted by frameless door windows, a feature more typical of classic sports coupes than large SUVs. The unmistakable light signature is provided by rear LED headlights connected by an elegant light strip.
• Chassis and maneuverability: Given the car's larger dimensions, the optional all-wheel steering is a crucial feature. At low speeds, it reduces the turning circle for easier city parking, while at higher speeds, it increases stability. Naturally, an adaptive air suspension for seamless ride height adjustment is included.
• Sport variants: For drivers seeking the ultimate experience, Audi offers the SQ8 and especially the RS Q8. The latter shares chassis and engine technology with its relative, the Lamborghini Urus, and is among the fastest SUVs on the market.

Mercedes-Benz GLS: The S-Class of SUVs and absolute comfort

Mercedes' largest SUV is designed from the ground up as the ultimate family cruiser, prioritizing maximum space, state-of-the-art assistance systems, and unparalleled passenger care.

• Infotainment and telematics: The MBUX (Mercedes-Benz User Experience) system dominates the interior via two interconnected 12.3-inch screens. It excels with innovative augmented reality (AR) navigation, which projects directional arrows and street names directly onto a live feed from the front camera, and advanced voice control that responds to natural commands ("Hey Mercedes").
• Innovative everyday features: A very practical and popular feature is the special Carwash mode. With a single button press, the car automatically folds the mirrors, closes all windows including the sunroof, deactivates the rain sensor, and raises the air suspension to its highest position for easier wheel arch cleaning.
• Chassis and electronics: The revolutionary E-Active Body Control active suspension uses cameras to scan the road ahead and prepare the dampers for bumps in advance. It also includes a unique "recovery mode" that can bounce the car to free it if it gets stuck in deep sand or mud.
• Maximum luxury and space: The GLS can accommodate up to seven passengers as standard, or offers a configuration with six individual seats (Captain's chairs). The pinnacle of the range, turning the vehicle into a mobile limousine, is the Mercedes-Maybach GLS version, featuring optional massaging rear seats, a built-in refrigerator, and a unique two-tone paint finish.

The Audi Q8 is an ideal choice for those looking for a prestigious and sporty SUV with an emphasis on attractive design and a premium feel on board. It is perfectly suited for couples or smaller families for whom style, dynamics, and driving experience are more important than maximum transport capacity.

The Mercedes-Benz GLS represents the absolute pinnacle of family luxury and is intended for demanding buyers who require a full seven-seater vehicle without any compromises in comfort and spaciousness. It is an ideal highway cruiser for long journeys, but one must expect that its size and weight bring higher maintenance costs and poorer maneuverability in the city.

Based on long-term user experience, service reports, and our detailed inspections, such as an independent car condition check, we have compiled an overview of the most common problems that used car buyers should watch out for.

Audi Q8

The Audi Q8 is a robust and precisely crafted SUV, but its complex electrical system and emission systems take their toll on used cars.

• Electronics and mild-hybrid system: By far the most common and serious problem with six-cylinder engines (especially the popular 50 TDI) is the failure of the 48V belt-driven starter-generator (BSG). This defect usually leads to a complete battery drain, electrical system error messages, and the need for a tow.
• Engine and transmission: Owners of 3.0 TDI diesel engines very often complain about a significant delay (so-called turbo lag) and hesitant reactions of the automatic transmission when pulling away from an intersection. Uploading the latest software update for the control unit at an authorized service center usually helps.
• Chassis and brake wear: Due to the high curb weight exceeding two tons, brake discs and pads wear out significantly faster. The air suspension is generally reliable, but older units with higher mileage may suffer from leaking air springs.
• Infotainment: The MMI Touch Response system with two displays occasionally freezes, restarts spontaneously, or has a slower startup immediately after starting the car.

Mercedes-Benz GLS

The Mercedes-Benz GLS offers extreme space and maximum luxury, but its massive dimensions and advanced technologies bring their own specific risks and high service costs.

• Electronics and EQ Boost system: Just like with Audi, mild-hybrid gasoline versions of Mercedes (e.g., GLS 450 or 580) struggle with the reliability of the 48V battery and starter-generator. The problem manifests as a yellow or red battery warning on the instrument cluster and can lead to the car failing to start.
• Airmatic air suspension: The adaptive suspension system is very comfortable but complex. At mileages approaching 100,000 km, there is a risk of compressor failure or leaks in the air struts themselves. In the case of the optional E-Active Body Control system, any repairs are extremely expensive.
• Interior and seat mechanisms: A frequent mechanical fault is the jamming of the electric motors for folding the third-row seats. Owners also occasionally report creaking plastics in the panoramic roof area or the dashboard when driving over larger bumps.
• Short tire life: The enormous weight approaching 2.5 tons and specific geometry mean an excessive load on the tires, which wear out disproportionately faster on this model than on other large SUVs.
• MBUX Infotainment: The user interface can encounter software glitches, from occasional rear parking camera failures to mobile phone pairing issues, which are usually resolved by over-the-air (OTA) updates.

When buying a used car, a thorough inspection is key. Here are some specific points to focus on for these two models, which is why an Independent technical inspection of the car should take place before every purchase, as it can detect potential hidden defects in their very complex technology in time.

When choosing an Audi Q8:

• Functionality of the 48V mild-hybrid system: In engines (especially the popular 50 TDI) from around 2019–2022, the belt-driven starter-generator (BSG) fails quite often. During the test drive, watch for warnings about a fault in the electrical network on the dashboard. If the car starts poorly or hesitates during the start-stop function, it could be a very expensive repair.
• Tiptronic gearbox behavior at low speeds: The eight-speed automatic in the Q8 can sometimes suffer from a noticeable delay when pulling away from an intersection or when downshifting. During the test drive, try to accelerate suddenly from a very low speed – the gearbox should react smoothly and without a harsh jerk.
• Wear and noise of frameless windows: The Audi Q8 features stylish frameless windows, which are, however, prone to precise closing. At highway speeds, listen carefully for excessive aerodynamic noise around the door seals. Sometimes only window calibration helps, other times it's a deformed seal.
• Adaptive air suspension test: Most of these cars are equipped with air suspension. On a flat surface, try manually switching to the highest and lowest modes. The compressor should not be excessively noisy and the car must rise evenly. The vehicle should not "sag" on one wheel after parking, which indicates a bellows leak or a valve problem.
• MMI system and camera stability: The pair of touchscreens can freeze or load navigation very slowly on older software versions. During the drive, test the response speed and check if the 360-degree parking camera activates smoothly and without delay when shifting into reverse.

When choosing a Mercedes-Benz GLS:

• Complex Airmatic or E-Active Body Control suspension: Due to the extreme weight of the car, suspension components suffer a bit more on used vehicles. Drive the car over speed bumps and listen for any dull thuds. For the optional E-Active Body Control system, check the smoothness of the lean and the absence of error messages – repairing its hydraulic elements is usually astronomically expensive.
• Electric rear seat adjustment: The GLS offers fully electric folding of the second and third rows of seats. Gradually test every button in the trunk and at the rear passenger doors. The motors can be tired or clogged with dirt in three- or four-year-old cars, which you can tell by the jerky movement of the backrests or complete non-functionality.
• Smoothness of the EQ Boost (ISG) system: The integrated starter-generator (ISG) in six-cylinder and eight-cylinder engines must ensure completely imperceptible engine shutdown and startup. If you feel unpleasant vibrations or delays when the start-stop system is activated, it may indicate a problem with the expensive 48V network.
• Interior creaking and plastic fitment: Although it is effectively the "S-Class among SUVs," models from the first years of production of this generation (around 2020) can sometimes be troubled by noises in the dashboard or in the second-row seat attachment mechanism. Deliberately choose a rougher country road or cobblestones during the test drive and listen to the interior.
• Brake system load: The Mercedes-Benz GLS commonly weighs well over 2.5 tons, which places huge demands on the brakes. Visually check the edge of the brake discs. During the drive, try braking from a higher speed – the steering wheel must not vibrate in your hands, which would clearly indicate warped front discs from overheating.

Sources: ADAC, novinky.cz, lidovky.cz, motorvize.cz, autozive.cz, veteran.cz

This article was prepared using artificial intelligence tools. The section guarantor is Petr Dušek.