The 2009 GL450 X164 with the M273 4.6L V8 is a capable luxury SUV plagued by catastrophic engine failure issues due to balance shaft defects, plus typical Mercedes aging drivetrain and cooling concerns that can add up fast.
Symptoms: Metal shavings in oil during changes, Check engine light with low oil pressure codes, Rattling or knocking noise from engine bay at startup or idle, Sudden catastrophic failure with complete engine seizure
Fix: The M273 balance shaft gears strip their bolts, sending metal through the engine and destroying bearings, camshafts, and cylinder walls. Requires complete engine rebuild or replacement. Preventive fix involves removing balance shafts before failure (12-16 hours labor). Full rebuild after failure: 25-35 hours labor plus machine work.
Symptoms: Pink milkshake appearance in transmission fluid, Coolant in transmission pan or transmission fluid in coolant reservoir, Transmission slipping or rough shifts after coolant intrusion, Engine overheating or coolant loss without external leaks
Fix: The 722.9 transmission cooler inside the radiator fails internally, allowing coolant and ATF to mix. Requires radiator replacement, transmission fluid flush (multiple), and often transmission rebuild if driven after contamination. Cooler replacement alone: 3-4 hours. Transmission rebuild adds 18-22 hours.
Symptoms: Vehicle sagging on one or both corners, especially after sitting overnight, Airmatic warning light on dash with fault codes, Compressor running constantly or excessively, Harsh ride or inability to adjust ride height
Fix: Air struts leak at seals, compressor fails from overwork, or valve block develops leaks. Struts are 2-3 hours each, compressor is 2.5-3.5 hours, valve block 4-5 hours. Most vehicles need multiple components by 100k miles. Aftermarket coil conversion available for $1,800-2,200 installed.
Estimated cost: $800-1,400 per strut, $1,200-1,800 compressor, $1,500-2,200 valve block
Front Lower Control Arm Bushings and Ball Joints
Common · medium severity
Typical onset: 60,000-100,000 mi
Symptoms: Clunking over bumps from front suspension, Wandering or loose steering feel, Uneven tire wear on inside edges, Vibration through steering wheel at highway speeds
Fix: The heavy GL450 eats front control arm bushings and ball joints. Mercedes sells entire control arm assemblies only—no serviceable bushings. Front lower arms are 2.5-3 hours per side and require alignment. Most need both sides plus upper arms eventually.
Estimated cost: $1,400-2,200 (both lower arms with alignment)
Intake Manifold Flap Actuators / Resonance Flaps
Occasional · medium severity
Typical onset: 70,000-120,000 mi
Symptoms: Check engine light with P2004, P2006, P2009, or P2015 codes, Loss of power at low RPM or sluggish acceleration, Rough idle or stumbling on acceleration, Rattling noise from intake manifold area
Fix: Plastic actuator arms and linkage rods break inside the intake manifold. Requires intake manifold removal and replacement of actuators or entire manifold. 6-8 hours labor to remove intake, diagnose, and replace failed components.
Estimated cost: $1,200-2,200
Transmission Mount and Engine Mount Deterioration
Common · low severity
Typical onset: 80,000-130,000 mi
Symptoms: Clunk or thud when shifting from Park to Drive or Reverse, Excessive vibration at idle in Drive, Shudder during acceleration from stop, Visible sagging or torn rubber on mount inspection
Fix: The heavy V8 and 7-speed transmission destroy mounts. Transmission mount is most common failure (2-2.5 hours). Engine mounts require more disassembly (3-4 hours each). Recommend replacing all mounts together for labor efficiency.
Estimated cost: $600-900 transmission mount, $1,800-2,800 all mounts
Owner tips
Check for balance shaft recall completion (code P73-60) or proactive delete—this is the single most important item on this engine
Flush transmission fluid every 40k miles and inspect for coolant contamination religiously
Budget $2,000-3,000 annually for suspension and drivetrain wear items after 80k miles
Get pre-purchase inspection with oil analysis and borescope inspection if buying used over 60k miles
Only buy if balance shaft delete is documented and you have a $5,000 repair fund—this is a ticking time bomb that drives beautifully until it grenades.
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: Located under front passenger seat; AGM battery required for vehicle electronics
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Every control module on the 2007-2012 Mercedes-Benz GL450 X164 — 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.
⚠️ One per front seat. Controls memory, heating, ventilation. Seat removal not required.
Bi-Xenon Control Unit (XCU)0.6 hr R&Raftermarket tool +0.2 hr▸ programming details
📍 Behind each headlight assembly (left and right)
🔧 Star Diagnosis or Autel MaxiSys
⚠️ One per headlight. Headlight removal required. Adaptive headlight calibration if equipped with AFS.
Fuel Pump Control Module (FPCM)no coding
📍 Integrated into SAM-R
⚠️ Not a separate module; fuel pump relay controlled by SAM-R. Replace SAM-R if faulty.
4MATIC Control Unit (4M)no coding
📍 Integrated into ESP/ABS module
⚠️ Not a separate module; 4MATIC logic integrated into ESP. No standalone replacement.
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 GL450 X164 4.6L V8 M273 and can vary by trim.
🔧 Database maintained under the daily editorial review of Chris Hackleman · Master Technician · 20+ years and Jeff Moore · Master Lexus & Toyota Mechanic · 20+ years.