Mercedes-Benz AMG A 45
The M139 is the logical development of the M133 and surpasses it in every respect: more power, better thermal management through an improved cooling concept, combined direct and port injection to fight intake valve carbon build-up. As a young engine with limited long-term data it is considered robust so far. Isolated reports of coolant sensor issues and water pump failures at high speeds. Tuning potential is enormous, but fuel supply must be upgraded at higher power levels.
A 45 AMG — Most Powerful Four-Cylinder
285 kW from a four-cylinder — unmatched worldwide at the time. The W177 AMG 45 is even sharper than the W176 and continues the legend.
Engine Weaknesses 6
The world's most powerful series-production four-cylinder at 421 hp subjects its turbocharger to extreme stress. Without adequate cool-down periods after full-load operation, premature bearing wear is likely.
Symptoms: Whistling at high load, oil mist in intake tract, power drop in heat
The high-performance turbocharger on the M139 can push oil into the intake tract due to excessive shaft play. Early vehicles were subject to a recall for turbocharger bearing defects.
Symptoms: Oil consumption without visible leaks, smoke cloud on cold start, power drop under high load
The M139 cooling system is designed at its limits. After extended high-load phases coolant temperature can reach critical values, especially in warm weather.
Symptoms: Coolant temperature warning after spirited driving, restricted engine power through thermal management
Individual owners report coolant temperature warnings at high-speed driving. Diagnosis: faulty coolant pump or sensor. Isolated cases, no systematic problem known.
Symptoms: Coolant temperature warning on display, especially at high speed (170+ km/h)
Despite combined direct and port injection the M139 can build up deposits on intake valves under intensive use. Considerably less than pure DI engines.
Symptoms: Slight hesitation at part throttle, minimal power loss, rarely noticeable
The M139 shows elevated oil consumption under high-load operation. As a high-performance engine with 7.0-litre oil capacity, regular oil level checks are mandatory.
Symptoms: Dropping oil level between service intervals, slight oil smell on hot engine
Vehicle Weaknesses 7
On 135,454 A-Class W177 vehicles (production Sept. 2017 – Feb. 2019) the A/C condensate drain hose was not correctly routed. Condensation water could enter the footwell and cause short circuits.
On A-Class W177 with DCT gearbox from the production period January 2018 to March 2020, the gearbox may have been underfilled with oil. Consequence: possible drivetrain failure and increased fire risk.
Defective A/C connections can lead to fire risk. A recall was issued. Affected vehicles should be checked for completion of the recall.
The dual clutch gearbox in the W177 exhibits juddering and rough pull-away between 1,500–2,000 RPM. At high mileages and in urban use the clutch packs wear prematurely. Software updates alleviate the problem but do not resolve it permanently.
The MBUX infotainment system freezes or restarts spontaneously. Navigation, Bluetooth and voice control fail. Software updates usually only temporarily resolve the problem.
The MBUX system in the W177 shows sporadic issues in practice: frozen screen, incorrect traffic sign recognition and Bluetooth connection drops. Software updates are needed; on older vehicles problems are persistent.
Due to the high quiescent current draw of the numerous control units and driver assistance systems in the W177, the starter battery is particularly at risk during short-distance use and seasonally operated vehicles.
Reports & Tests
71 owner complaints filed with NHTSA (2018–2025). Most reported: Electrical (24), Other (20), Engine (14).