The 2009 G55 AMG is a hand-built supercharged beast with legendary off-road capability and surprising reliability for its performance level, but the M113K engine can grenade catastrophically when supercharger bearings fail or connecting rod bearings starve for oil under high-load conditions—often with zero warning.
Symptoms: Sudden metallic knocking from engine bay, Catastrophic loss of power, Metal shavings in oil, Check engine light with multiple misfires, Engine seizes completely in worst cases
Fix: Total engine rebuild or short block replacement required. Remove engine, disassemble, replace all bearings, pistons, rings, and machine work. 40-60 hours labor plus parts. Many shops recommend complete reman longblock to avoid repeat failures.
Estimated cost: $15,000-25,000
Supercharger Bearing and Coupler Failure
Common · high severity
Typical onset: 70,000-120,000 mi
Symptoms: High-pitched whine or grinding from supercharger, Loss of boost pressure, Metal debris in intake tract, Sudden power loss, Smoke from engine bay if impeller contact occurs
Fix: Supercharger must come off for bearing replacement or full rebuild. If caught early, bearing replacement alone (12-16 hours). If run too long, internal damage requires complete supercharger rebuild or replacement unit. Input shaft coupler often replaced simultaneously.
Estimated cost: $3,500-8,000
Transmission Oil Cooler Line Leaks
Common · medium severity
Typical onset: 60,000-100,000 mi
Symptoms: Transmission fluid puddles under vehicle, Burnt transmission fluid smell, Transmission running hotter than normal, Pink/red fluid stains on frame rails, Low fluid warnings on dash
Fix: Steel transmission cooler lines rust through where they pass along frame. Replacement requires lift access, sometimes cutting/fabricating new lines. 4-6 hours labor. Lines often replaced with upgraded stainless or rubber high-pressure hose sections.
Estimated cost: $800-1,500
Transmission Mount Failure
Common · medium severity
Typical onset: 50,000-90,000 mi
Symptoms: Clunking when shifting from Park to Drive/Reverse, Vibration at idle that changes when shifting, Visible transmission sag when inspected from below, Harsh engagement into gear
Fix: Rubber transmission mount deteriorates from heat and stress. Support transmission with jack, unbolt mount, replace. Often done with transfer case mount simultaneously. 2-3 hours labor for both.
Estimated cost: $600-1,200
Air Suspension Compressor and Strut Failures
Occasional · medium severity
Typical onset: 70,000-110,000 mi
Symptoms: Vehicle sits low on one or more corners, Compressor runs constantly, Suspension warning light, Harsh ride quality, Hissing sounds from corners when parked
Fix: Airmatic struts develop leaks at seals; compressor overworks and burns out. Individual strut replacement 2-3 hours each. Compressor replacement 3-4 hours. Many owners convert to coilover suspension to eliminate recurring costs.
Estimated cost: $1,200-2,500 per strut, $1,800-2,800 compressor, $4,000-6,000 coilover conversion
Fuel Pump and Filter Issues
Occasional · medium severity
Typical onset: 90,000-130,000 mi
Symptoms: Hard starting when hot, Loss of power under hard acceleration, Fuel starvation feel at high RPM, Check engine light with lean codes, Stumbling during full-throttle runs
Fix: In-tank fuel pump fails or inline fuel filter clogs. Filter replacement is 1-2 hours. Pump requires tank drop (6-8 hours labor). Supercharged engines very sensitive to fuel pressure drops. Both often done together preventively.
Symptoms: Oil seepage visible on valve covers, Burning oil smell from engine bay, Oil drips on exhaust manifolds causing smoke, Low oil warnings more frequent
Fix: Valve cover gaskets harden and leak. Both covers need removal, gasket replacement, cam position sensor seals replaced simultaneously. 6-8 hours labor. Not urgent but prevents bigger messes and oil consumption.
Estimated cost: $1,200-2,000
Owner tips
Change oil religiously every 5,000 miles with quality 0W-40 synthetic—bearing failures often trace to extended drain intervals or low oil levels
Inspect supercharger coupler and listen for bearing noise every oil change; catching whine early saves $10K+ in engine damage
Use Mercedes-approved transmission fluid only; 722.6 transmission is sensitive to fluid spec and deteriorates rapidly with wrong fluid
Budget $3,000-5,000 annually for maintenance and repairs beyond normal wear items—this is a hand-built AMG, not a Camry
Have compression and leak-down test done during pre-purchase inspection; these engines either run perfectly or are time bombs with weak rings
Buy one only if you have a $10K emergency fund and find a meticulously maintained example with full service records—when healthy they're incredible, but engine failures are financially catastrophic and often happen without warning.
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.
Fitment notes: H9 group also compatible; battery located in engine compartment passenger side
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Every control module on the 2008-2012 Mercedes-Benz G55 AMG — where it lives, replacement time, and what it takes to program a replacement. Modules marked dealer / factory tool won't work after a part swap alone — budget for programming.
⚠️ Memory seat function; position relearn required after replacement.
Fuel Pump Control Module (FPCM)no coding
📍 Rear cargo area, integrated with SAM-R
⚠️ Function integrated into SAM-R; no separate module. Relay replacement only.
Pre-Safe Control Unit (PSM)no coding
📍 Center console area, integrated with SRS
⚠️ Function integrated into SRS module on this generation; no separate unit.
Aftermarket tool coverage varies by software version and vehicle build — treat "aftermarket tool" rows as "usually possible" and verify against your tool maker's coverage list before promising a customer. Spot a wrong location or hour? Tell us — corrections ship fast here.
Size-standard part numbers — verify your connector type before buying. Rear blades are model-specific; check the package's vehicle list.
Fuel economy figures are EPA data via fueleconomy.gov (median across matching trims). Performance figures are compiled estimates for the 2009 Mercedes-Benz G55 AMG 5.4L V8 Supercharged M113K and can vary by trim.
🔧 Database maintained under the daily editorial review of Chris Hackleman · Master Technician · 20+ years.