Mercedes-Benz AMG SL 43
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.
Open-Top Pleasure
280 kW open-top — wind in the hair and power under the bonnet.
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 6
On the R232 with V8 engine, the starter-generator wiring harness can be damaged by friction against the driveshaft. Fire risk and drive loss. 12,341 vehicles affected.
The roof frame trim above the windscreen was not adequately secured on 795 vehicles and could detach while driving -- risk of accident.
On 795 vehicles worldwide, the roof frame trim above the windscreen was not adequately secured. The trim could detach while driving and endanger other road users.
The R232 draws excessive quiescent current through permanent internet connections. After just a few days standing, the 12V battery is too weak to start.
Jerky downshifts into lower gears at low speeds have been reported on the R232. Software updates as a remedy.
The 12V battery of the R232 discharges completely after just a few days standing. The cause is high quiescent current draw from always-on systems. Mercedes proposed retrofitting a CTEK charger in the boot.
Reports & Tests
9 owner complaints filed with NHTSA (2021–2025). Most reported: Electrical (5), Engine (4), Lane Departure (1).