2017 MERCEDES-BENZ GLS63 AMG

Typical onset: 40,000-80,000 mi

Symptoms: Excessive oil consumption (quart per 500-1000 miles), Blue smoke on cold starts or under hard acceleration, Metallic rattling or knocking from cylinder bank, Check engine light with misfire codes (P0300-P0308), Loss of compression on one or more cylinders

Fix: This is the M157's Achilles heel — thin Nikasil cylinder liners wear prematurely, allowing pistons to score the bores. Only permanent fix is complete engine rebuild with resleeved cylinders or used/reman engine replacement. Rebuild takes 40-60 hours labor, replacement engine 25-35 hours. Mercedes issued extended warranty on some VINs but 2017s are mostly out of coverage now.

Estimated cost: $18,000-35,000

Typical onset: 60,000-100,000 mi

Symptoms: Rattling or whirring noise from front of engine at idle, Noise increases with RPM then disappears above 2000 RPM, Check engine light with camshaft correlation codes, Metal shavings in oil during changes, Engine runs rough or fails to start after sitting

Fix: M157 balance shaft module and timing chain guides wear, causing chain slap and potential timing jump. Requires front engine disassembly including radiator removal, timing cover, chains, guides, tensioners, balance shaft module, and cam adjusters. Critical to inspect oil pump drive gear simultaneously. 18-25 hours labor depending on additional damage found.

Estimated cost: $6,500-11,000

Typical onset: 50,000-90,000 mi

Symptoms: Rough idle and hesitation under acceleration, Oil in intake tract or intercooler pipes, White or blue smoke from exhaust, P2006, P2004 intake manifold runner codes, Oil consumption without visible leaks, Collapsed or oil-soaked air filter

Fix: The PCV valve integrates into valve covers and oil separator fails, allowing oil into intake system and creating vacuum leaks. Requires both valve cover assemblies (they're not serviceable separately on M157) plus intake manifold cleaning. Often find damaged intake manifold runners requiring manifold replacement too. 8-12 hours labor for covers, add 4 hours if manifold needed.

Estimated cost: $3,200-5,800

Typical onset: 60,000-120,000 mi

Symptoms: Transmission fluid puddles under vehicle center, Burnt transmission fluid smell, Transmission temperature warning on dash, Harsh or delayed shifts when fluid gets low, Red fluid visible along transmission bellhousing seam

Fix: The 7-speed MCT transmission cooler lines corrode where they connect to the cooler and transmission, especially the quick-disconnect fittings. Lines run through crossmember requiring subframe drop for proper access. Replace all cooler lines as a set plus transmission fluid/filter service. 6-8 hours labor. Do NOT drive with low trans fluid or you'll grenade the MCT.

Estimated cost: $1,800-2,800

Typical onset: 70,000-110,000 mi

Symptoms: Vehicle sagging at one corner, especially overnight, Airmatic suspension warning on dash, Compressor running excessively (hear it cycling frequently), Rough ride quality or bottoming out over bumps, Visible fluid leak on strut body

Fix: Airmatic struts develop seal leaks or the air bladder separates. Front struts 3-4 hours each, rears 2-3 hours. Compressor often overworks trying to compensate and fails simultaneously — add 4 hours if compressor needed. Replace struts in pairs per axle. Must perform Airmatic calibration with Star Diagnostics after replacement or ride height will be incorrect.

Estimated cost: $2,800-4,500 per axle, $5,500-7,500 if compressor included

Typical onset: 80,000-130,000 mi

Symptoms: Grinding or whining noise that changes with speed, Clunking when shifting from Park to Drive, Vibration at highway speeds (55-70 MPH), 4MATIC warning light illuminated, Metal shavings in transfer case fluid

Fix: The transfer case chain stretches from torque load (this thing makes 560+ lb-ft) and bearings wear prematurely. Requires transfer case removal and complete rebuild or replacement unit. Rebuild 12-16 hours, replacement 8-10 hours. Used units from low-mile wrecks are common and cost-effective if you verify build date and service history. Update transfer case fluid to latest spec during any work.

Estimated cost: $4,500-7,000 rebuild, $3,500-5,500 replacement