The Mercedes-Benz GLS is the brand's flagship full-size seven-seat luxury SUV, competing directly with the BMW X7 and Range Rover. The current X167 generation arrived in Australia in 2019, replacing the X166 with a substantially revised line-up: the M256 3.0-litre inline-six petrol (GLS 450), the OM656 3.0-litre inline-six diesel (GLS 400d), a 48V mild-hybrid EQ Boost system, the 9G-TRONIC nine-speed automatic, AIRMATIC or E-ACTIVE BODY CONTROL air suspension, and the debut of the MBUX infotainment platform. It is a technologically impressive machine — and a genuinely complex one. Used X167 examples from 2019 onwards have attracted a meaningful number of documented complaints and several Australian recall actions, making careful pre-purchase research essential.
AIRMATIC air suspension faults
Air suspension is the most talked-about reliability concern for the X167 GLS. All Australian models use either AIRMATIC or the full E-ACTIVE BODY CONTROL system, both dependent on air struts, a compressor, and an electronic control unit.
- Air spring leaks are the most common failure. The rubber bellows crack with age or heat, causing one corner to sag — most obvious after the car sits overnight. A single air spring replacement runs $1,500–$2,500 per corner at dealer rates.
- Compressor burnout follows an unaddressed air spring leak: the compressor runs continuously trying to maintain pressure and fails. Add another $1,200–$2,000 on top of strut costs.
- AIRMATIC control unit software fault: Mercedes-Benz issued a technical service bulletin for the W167/X167 platform covering an "AIRMATIC fault" dashboard warning caused by an internal control unit software error (fault codes C220C04/C220C06), not a mechanical strut failure. The remedy is a software update; strut replacement will not clear this fault.
A full air suspension overhaul covering multiple components can reach $5,000–$8,000+ at dealership rates. Early intervention on any sagging corner is essential — a $2,000 repair left unattended can become a $6,000 job.
48V EQ Boost electrical system
The GLS 450's 48-volt mild-hybrid system has generated significant owner complaints and two confirmed Australian recall actions.
- 48V wiring harness fire risk (REC-005948): A manufacturing defect meant the threaded nut securing the 48V wiring harness under the driver's seat may not have been correctly torqued. A loose connection can overheat, posing a fire risk and causing widespread electrical faults. This recall covered GLE and GLS (167 series) vehicles built between 2019 and 2022.
- A/C drain water intrusion (REC-005676): A separate 2019 GLE/GLS recall (221 vehicles, published May 2023) found that air-conditioning drain hoses may have been incorrectly installed, allowing condensation to enter the cabin and short-circuit electrical systems — with potential consequences including eCall failure, inability to start, and fire risk.
- 48V battery failure: Some owners report sudden "48V battery malfunction" warnings, loss of stop/start, reduced acceleration, and in severe cases a no-start condition that a conventional jump-start cannot fix. Repairs range from $1,500 to $5,000+ depending on whether software recalibration or hardware replacement is needed.
M256 petrol engine: oil consumption
The M256 inline-six is technically sophisticated but has a documented tendency for above-average oil consumption in some examples, with piston ring wear cited by workshops as a probable cause. Mercedes recommends checking the oil every 5,000 km — important given the 25,000 km service interval. Some owners have also reported cylinder misfires (notably cylinders 3–4 at higher revs), though these appear less widespread and may relate to ignition coil or injector faults rather than a systemic engine issue. The electric auxiliary coolant pump is another component worth inspecting; pump failure can cause overheating.
OM656 diesel: DPF & AdBlue
The GLS 400d's OM656 diesel suits Australian highway conditions well, but urban use can block the diesel particulate filter (DPF). Short suburban trips prevent the DPF from completing full regeneration cycles, triggering warning lights, reduced power, and eventually limp-home mode. Keeping AdBlue topped up (required for the SCR system) and running regular highway stints prevents most issues. A blocked DPF that cannot be regenerated in-service may require replacement at $2,500–$5,000+.
9G-TRONIC transmission: shudder & recall
The nine-speed automatic is generally smooth but owners have reported low-speed shudder or hesitation during light acceleration, linked to torque converter clutch behaviour or fluid condition. A confirmed Australian recall (REC-005922) covered 4,837 GLE and GLS (167 series) vehicles built between 2019 and 2023 for a transmission control module software fault that could cause an unexpected downshift and sudden loss of engine power. The fix is a free software update. Transmission fluid changes around every 60,000–80,000 km are strongly recommended despite Mercedes' "lifetime fill" designation, to prevent shudder and solenoid wear.
MBUX infotainment glitches
The X167 introduced first-generation MBUX and early software was unreliable. Reported issues include screen freezing or going black on startup (sometimes requiring a 10-second steering wheel button reset), rearview camera interruptions, Bluetooth dropouts, and navigation errors. The rearview camera failure was serious enough to trigger a US recall (NHTSA #21V354) for 2019–2021 167-platform vehicles — buyers should verify Australian examples have received dealer software updates that address these faults. Persistent display hardware failures are expensive to fix out of warranty.
Servicing costs
The GLS is among the costliest vehicles to maintain in Australia. Mercedes-Benz's capped-price servicing runs approximately $1,100 per scheduled service (every 12 months or 25,000 km), with a three-service bundle around $3,300. This covers routine items only — any air suspension work, 48V system repairs, transmission fluid, tyre replacements on large-diameter staggered fitments, or brake service adds substantially. Budget ownership of an X167 GLS is not realistic; prospective buyers should factor ongoing maintenance costs into their purchase decision from the outset.
Recalls & safety
The Mercedes-Benz GLS X167 has been subject to multiple recall actions in Australia. Confirmed recalls affecting 2019-model vehicles include the 48V wiring harness fire risk (REC-005948), the A/C drain water intrusion electrical fault (REC-005676), and the transmission software power-loss fault (REC-005922). Carify has recall data mapped against the 2019 GLS recall page — always cross-reference any vehicle's VIN on vehiclerecalls.gov.au to confirm all outstanding work has been completed. You can also explore the full car problems and recalls hub for a broader overview.
Buying a used Mercedes-Benz GLS? What to check
- Air suspension: Park overnight and check ride height in the morning — any sagging corner signals a leak. Listen for compressor noise and check for suspension warnings during the test drive.
- 48V recall status: Confirm REC-005948 (fire risk) and REC-005676 (A/C drain) have been rectified on the specific vehicle. Ask for dealer documentation.
- Transmission: Test the 9G-TRONIC across all drive modes; shudder at low speed warrants specialist inspection. Confirm the REC-005922 software update has been applied.
- MBUX: Test the rearview camera, screen responsiveness, and Bluetooth before committing. A poor-functioning display may need a reflash or hardware replacement.
- Engine oil level: Check it even on low-mileage cars — M256 oil consumption can occur between scheduled services.
- Service history: Insist on a complete Mercedes-Benz stamped history. Any gap in records on a vehicle this complex is a serious concern.
- Finance check: Run a PPSR check to confirm no money is outstanding before you buy, and consider a full VIN check for write-off and odometer history.
The verdict
The Mercedes-Benz GLS X167 delivers genuine flagship-level luxury with seven seats and an impressive suite of technology. But that same technology — AIRMATIC suspension, 48V mild-hybrid, MBUX, and the 9G-TRONIC — has produced documented reliability weak points and multiple Australian recall actions. Out-of-warranty repair bills can be substantial. Buyers who demand full service history, verify all recall rectifications, and budget realistically for high-end European running costs will find the GLS a rewarding ownership proposition. Those expecting worry-free motoring on the cheap are likely to be disappointed.