The 2022 GLS450 X167 with M256 3.0L inline-six is still relatively new, but early patterns show the EQ Boost 48V mild-hybrid system and ISG (Integrated Starter-Generator) causing issues, plus occasional turbocharger oil seepage and transmission cooler leaks. The severe engine jobs listed (pistons, bearings, rebuilds) are outliers—typically catastrophic failures from oil starvation or neglected maintenance rather than design flaws.
ISG (Integrated Starter-Generator) Failure
Occasional · high severityTypical onset: 40,000-80,000 mi
Symptoms: Check engine light with P138A00 or P138B00 codes (ISG position sensor), Rough start-stop operation or complete failure of start-stop function, Intermittent no-start condition—vehicle won't crank, 48V battery warning on dash
Fix: ISG unit is sandwiched between engine and transmission—requires trans removal or significant subframe drop depending on shop approach. Book time is 12-16 hours for full R&R. Mercedes updated ISG software multiple times, but hardware failure requires replacement. Some early '21-'22 units had bearing issues.
Estimated cost: $5,500-8,000
Transmission Oil Cooler Line Leaks
Common · medium severityTypical onset: 30,000-70,000 mi
Symptoms: Transmission fluid puddle under vehicle center/front, Low transmission fluid warning or limp mode, Lines weep at crimp connections or cooler inlet/outlet
Fix: 9G-Tronic cooler lines on X167 have quick-disconnect fittings that can weep or crack. Cooler itself sometimes develops pinhole leaks. Line replacement is 3-5 hours depending on access; cooler replacement adds another 2-3 hours if failed. Requires fluid refill and ATF level calibration via Xentry.
Estimated cost: $800-1,800
Turbocharger Oil Feed Line Seepage
Occasional · medium severityTypical onset: 50,000-90,000 mi
Symptoms: Oil smell from engine bay, especially after highway runs, Small oil drips on undertray near turbo, Visible oil wetness on turbo housing or feed line banjo bolt
Fix: M256 turbo oil feed uses crush washers at banjo connections—these can weep over time, especially if overtorqued during previous service. Occasionally the feed line itself cracks. Replacement involves partial intake removal for access—4-6 hours. Not catastrophic but can lead to turbo starvation if ignored long-term.
Estimated cost: $600-1,200
Fuel Filter Housing Cracks
Occasional · medium severitySymptoms: Fuel smell in engine bay or cabin, Hard start or extended crank, especially when hot, Check engine light for fuel pressure deviation (P0087, P0088), Visible fuel weeping on driver-side cylinder head area
Fix: Plastic fuel filter housing on M256 can crack at mounting boss or seam—seems related to heat cycling and vibration. Filter is integrated, so housing replacement required. 2-3 hours labor, includes fuel system depressurization. Mercedes issued updated part numbers for reinforced housings mid-production.
Estimated cost: $500-900
Airmatic Suspension Compressor Relay Cycling / Failure
Occasional · medium severityTypical onset: 60,000-100,000 mi
Symptoms: Suspension compressor runs excessively or constantly, Vehicle sags overnight or after sitting, Airmatic warning on dash: 'Vehicle too low' or 'Malfunction visit workshop', Compressor overheats and shuts down
Fix: X167 Airmatic uses updated ADS Plus struts, but compressor and valve block still fail. Common culprits: leaking air spring (strut), valve block solenoid, or compressor itself. Diagnosis requires leak test and Xentry pressure readings. Compressor replacement 3-4 hours, valve block 4-6 hours, single strut 2-3 hours. Air spring leaks often show as oily residue at lower bellows.
Estimated cost: $1,200-3,500
Catastrophic Engine Failure from Oil Starvation (Rare but Documented)
Rare · high severityTypical onset: 20,000-60,000 mi
Symptoms: Sudden catastrophic knock or rattle, Metal debris in oil or on magnetic drain plug, Rod bearing failure or spun bearing—often follows low oil event, Seized engine or total loss of power
Fix: The severe jobs listed (pistons, bearings, short block, rebuild) result from oil starvation—usually owner neglect (extended oil change intervals, ignoring low oil warnings) or very rare oil pump failure. M256 has direct injection and runs hot; needs MB 229.52 spec oil changed at 10k max. Engine rebuild or short block replacement runs 40-60 hours labor. This is NOT a common pattern failure—treat as outlier.
Estimated cost: $15,000-25,000
Solid powertrain with EQ Boost complexity—buy a CPO or extended warranty if going used; ISG and Airmatic repairs get expensive fast outside warranty.
AI-assisted summary drawn from NHTSA recall data, our labor-times database, and platform knowledge. Not a substitute for a pre-purchase inspection on a specific vehicle.