The Second Generation: X166 (2013–2019)
Originally launched as the GL-Class and later rebranded as the GLS in 2016, the X166 generation is a massive, incredibly comfortable cruiser. However, it is now entering an age where major components like the Airmatic suspension and turbochargers require expensive attention.
The diesel models (GLS 350d) are popular for their torque but can suffer from complex AdBlue system failures and oil cooler leaks. Petrol V8 models are smoother but exceptionally thirsty and can develop timing chain rattle if oil changes were neglected.
- Airmatic suspension: Check for sagging or a compressor that runs constantly.
- Inspect the oil cooler seals on V6 diesel engines (OM642).
- Verify all three rows of power-folding seats operate without hesitation.
The Modern Giant: X167 (2020–Present)
The X167 generation brought a massive upgrade in cabin technology with the MBUX system and the introduction of 48V mild-hybrid systems. These new technologies provide better efficiency and comfort but have also introduced '48V battery malfunction' issues that can leave the car stranded.
Build quality is generally high, but some early owners have reported rattles from the panoramic sunroof and software glitches in the infotainment system. Purchasing a Certified Pre-Owned (CPO) example is highly recommended for this generation.
- Ensure the 48V battery and associated software have been updated.
- Listen for wind noise or rattles from the large panoramic roof.
- Test every screen and touch control in the MBUX high-definition cockpit.
The Airmatic Reality Check
Air suspension is the defining feature of the GLS's ride quality, but it is also its most predictable high-cost repair. It's not a matter of 'if' the air bags will leak, but 'when.' A typical dealership replacement for all four corners can easily exceed $5,000.
When inspecting a used GLS, look for a car that sits level after being parked overnight. If the front or rear is slammed, the bags or the valve block are failing. A compressor that makes excessive noise is also a sign it's working too hard to compensate for leaks.
- Listen for a loud or vibrating compressor under the front wheel arch.
- Check for cracks in the rubber bellows of the air struts.
- Verify the 'Raise Vehicle' function raises the car quickly and evenly.
Best Configurations For Reliability
For those seeking the lowest long-term risk, the GLS 450 with the inline-6 engine (post-2020) or the facelifted 2017-2019 X166 models are the strongest choices. These avoid the extreme complexity of the V8 engines and the emissions-heavy diesel variants.
Regardless of the model, a full service history with records of transmission fluid changes and brake replacements (which wear fast on this 2.5-ton vehicle) is non-negotiable.