The 2020 A45 AMG W177 with the M139 2.0L turbo is Mercedes' most powerful production four-cylinder, pushing 416 hp through an 8-speed DCT. Early examples are showing serious engine durability issues under hard use, particularly bearing and piston failures, plus transmission cooling problems that can cascade into expensive replacements.
Connecting Rod and Main Bearing Failure
Occasional · high severityTypical onset: 30,000-60,000 mi
Symptoms: metallic knocking from lower engine block especially when cold, low oil pressure warning, metal shavings in oil during change, catastrophic failure with loss of power
Fix: Full engine teardown to inspect crank journals and replace bearings, often requires crankshaft machining or replacement. If caught early, bearing replacement alone runs 18-24 hours labor. If the crank is scored, you're looking at short block replacement or full rebuild at 35-45 hours.
Estimated cost: $8,000-18,000
Piston Ring Land Cracking and Piston Failure
Occasional · high severityTypical onset: 40,000-70,000 mi
Symptoms: excessive oil consumption (1 qt per 1000 mi or more), blue smoke on startup or under boost, misfires under load, loss of compression in one or more cylinders
Fix: Complete top-end rebuild with piston and ring replacement. All four pistons should be done together. Cylinder bore inspection required—if scoring present, needs full short block. Labor runs 28-35 hours for piston replacement with honing, more if block needs replacement.
Estimated cost: $9,000-16,000
AMG Speedshift DCT Transmission Oil Cooler Failure
Common · medium severityTypical onset: 25,000-50,000 mi
Symptoms: transmission overheating warning on dash, harsh shifts when hot, slipping between gears under acceleration, burnt ATF smell, trans temp exceeding 230°F in normal driving
Fix: Replace transmission oil cooler and flush ATF system. Cooler is integrated into the bottom pan area. If caught early, just cooler replacement at 4-6 hours labor. If driven hot for extended periods, clutch packs may be damaged requiring full trans rebuild.
Estimated cost: $1,800-3,200
Transmission Mount Failure
Common · low severityTypical onset: 35,000-60,000 mi
Symptoms: clunking when shifting from park to drive, excessive vibration at idle, lurching during aggressive launches, visible separation or tearing of rubber mount
Fix: Replace transmission mount assembly. The high torque output accelerates mount degradation. Straightforward job at 2-3 hours labor including subframe access.
Estimated cost: $600-1,000
Head Gasket Failure (Both Cylinder Banks)
Rare · high severityTypical onset: 50,000-80,000 mi
Symptoms: coolant loss with no visible leaks, white smoke from exhaust, overheating under boost, oil in coolant reservoir or coolant in oil, rough idle and misfires
Fix: Both head gaskets must be replaced as a pair on this inline-four. Requires complete head removal, surface inspection, and valve job if warping occurred. Plan for 20-26 hours labor. If heads are warped beyond spec, add machining or replacement costs.
Estimated cost: $6,500-10,000
High-Pressure Fuel System and Filter Issues
Occasional · medium severitySymptoms: intermittent check engine light with fuel pressure codes (P0087, P0088), rough running under boost, hesitation or stumble during hard acceleration, long crank times especially when hot
Fix: High-pressure fuel pump or fuel filter clogging from contaminated fuel. Filter is not serviceable on regular intervals per MB, but early carbon buildup clogs it. Pump replacement runs 5-7 hours, filter access requires fuel tank drop adding 3-4 hours.
Estimated cost: $1,500-2,800
High-performance bargain with serious reliability risks—only buy with full service records and budget $3-5k annually for repairs, or wait for 2022+ models with revised bearing specs.
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.