"The M133 engines are generally reliable and solid units, as long as you don't push them beyond their limits — operating at or over 30 psi and expecting long-term reliability is completely unrealistic."
RISKY
62/ 100
"Fast thrills, expensive bills ahead"
—
Max HP
—
Torque Nm
10,000
Oil interval km
0
Recalls
6
Known issues
Known Issues
Oil Infiltration into Engine Wiring Harness€1,500-4,000 · 60,000-150,000 kmCRITICAL
Oil migrates into the engine wiring harness, causing widespread electrical faults, sensor failures, and ECU communication errors. Reported across M133 and related AMG engines. Mercedes has offered no official remedy or goodwill outside of warranty, leaving owners fully exposed to repair costs.
Fuel System Failures – Pump and Control Module€600-2,000 · 50,000-120,000 kmHIGH
Persistent fuel system issues reported including fuel pump failures, wiring/connector faults, and fuel pump control module failures. Symptoms can be intermittent, making diagnosis difficult. Owners have reported recurring faults even after partial repairs.
Hard starting or no-start condition
Intermittent stalling
Fuel pressure drop under load
Engine hesitation at high RPM
DIY: Moderate
Turbocharger Wear and Anti-Surge Valve Issues€1,200-3,500 · 80,000-160,000 kmHIGH
The Borg Warner turbocharger fitted to the M133 is known to suffer from wear, especially on tuned or hard-driven examples. Anti-surge valve issues can cause compressor surge, accelerating turbo wear. High boost pressures above factory spec dramatically shorten turbo life.
Boost pressure irregularities
Audible compressor surge or flutter
Turbo lag increasing over time
Blue smoke on acceleration
DIY: Hard
Thermal Management / Power Reduction in Hot Conditions€200-800 · 0-200,000 kmMODERATE
The M133 exhibits significant power reduction when heat-soaked during track or aggressive driving conditions. This is a known characteristic of the engine and its thermal management strategy, limiting sustained performance use.
Noticeable power loss during spirited or track driving
Engine pulling timing under sustained load
Reduced boost pressure when engine temperature is elevated
DIY: Easy
MAF Sensor and Throttle Body Seal Deterioration€150-600 · 60,000-130,000 kmMODERATE
MAF sensor inaccuracies and deteriorating throttle body seals have been reported, causing surging, pulsing throttle response, and idle instability. Seal fitment is model-year specific and care is needed to ensure correct part application.
Mercedes designed the M133 to discourage traditional rebuilding, preferring full engine replacement. Aftermarket cylinder sleeves are available from specialist suppliers but the process is non-standard, raising long-term rebuild costs and complicating ownership at high mileage.
High oil consumption at high mileage
Compression loss across cylinders
DIY: Expert
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Buying Checklist
Connect a Mercedes-compatible diagnostic tool and check for any stored fault codes, especially fuel system, boost, and electrical codes
Physically inspect the engine wiring harness and connectors for any signs of oil contamination or corrosion
Request full service history and verify oil changes were performed at or below 10,000 km intervals with the correct MB-approved spec oil
Ask specifically whether the car has been tuned, remapped, or run at elevated boost — inspect for aftermarket intercooler, intake, or exhaust modifications
During a test drive, perform sustained hard acceleration to check for turbo surge, power hesitation, or thermal power reduction symptoms
Check for any oil leaks around the turbocharger, valve cover, and cam cover, and inspect the coolant for any signs of contamination
Service Reality
Community oil interval10,000 km
Oil specificationMB 229.5 or 229.51, 5W-40 or 0W-40 fully synthetic
Est. ownership cost (2yr)€2,500–5,000 per year depending on mileage, condition, and whether major components such as the turbo or wiring harness require attention
The Mercedes A45 AMG M133 is a genuinely impressive performance engine that delivers extraordinary power from a small displacement, but it carries meaningful reliability risks that buyers must take seriously. The wiring harness oil contamination issue is particularly concerning as Mercedes has offered owners no official remedy, meaning any used example could be carrying a costly hidden problem. Avoid any car showing signs of aggressive tuning, as operation above factory boost levels dramatically shortens turbo and engine life. Budget for higher-than-average maintenance costs and always insist on a pre-purchase inspection by a Mercedes specialist before committing.