Overview
Community orientation
The X166 platform (GL-Class 2012–2015 / GLS-Class 2015–2019) is the full-size sibling of the W166 and shares its spine engines: the M276 V6 petrol (GLS 400), the M278 V8 petrol (GL 500 / GLS 500), and the OM642 V6 diesel (GL 350 BlueTEC / GLS 350d). The entire range is 4MATIC only. The 2015 rename from GL to GLS was cosmetic — the platform and powertrains were unchanged. The generation adds no new occurrence patterns of its own; those patterns resolve at the engine level onto the applicable build windows. Community orientation only, not a reliability rating or a purchase recommendation.
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Filtered: M278 · 4.7L V8 biturbo (M278).
Known issues
Sorted by severity. Tap an issue to reveal its symptom, repair and what to check.
Engines & reliability
Tap a row to filter the issues to that engine.
Pre-purchase checklist
Cold start
- ☐Start the engine cold and listen for a timing-chain rattle in the first seconds
Diagnostics
- ☐Scan stored DTCs and check live fuel/ignition/boost data before the test drive