Mercedes A45 AMG M133
"Mine's at 90k on the original turbo and harness, no issues yet, but every A45 thread has someone with the oil-in-the-wiring problem and Mercedes just tells them tough luck, out of warranty, pay up."
Power Variants
Recommendation
Do not choose between the 360hp and 381hp M133 based on power alone. The facelift's higher output comes from a factory recalibration, not a weaker part, so it is not a red flag by itself. What matters more on both versions is documented oil change history at or below 10,000 km, physical confirmation the wiring harness is dry, and proof the car has never been run at boost levels above factory spec. A well maintained pre-facelift car is a safer buy than a neglected or tuned facelift car.
Known Issues
Oil Infiltration into Engine Wiring HarnessCRITICAL
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 ModuleHIGH
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.
Turbocharger Wear and Anti-Surge Valve IssuesHIGH
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.
Thermal Management / Power Reduction in Hot ConditionsMODERATE
The M133 exhibits noticeable 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 rather than indicating a fault in most cases.
MAF Sensor and Throttle Body Seal DeteriorationMODERATE
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.
Engine Rebuild Difficulty, Proprietary Sleeve DesignLOW
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.
Buying Checklist
Service Reality
Strong Points
Also Found In
Time Bomb Parts Inspect Proactively
Tuning Risk If This Example Has Been Modified
HIGHA tune on this ECU can generally be reverted to a stock-reading file; at least one tuner for this exact engine explicitly notes that many customers flash back to stock before a dealer service visit. Separately, and critically important for this specific engine independent of any tuning history: early production cars (around 2014) shipped from the factory without an anti-surge valve on the turbocharger, a genuine design flaw that let excess boost pressure escape only through the turbo impeller itself, causing premature bearing wear and turbo failure. Mercedes issued a recall to retrofit the fix, but multiple sources note many used examples on the market today never had this recall work completed, making this a critical, tuning-independent check for any buyer.
This is one of the more unambiguous cases in this database of a specialist source directly stating that tuning itself materially raises risk on an already-marginal factory design: additional boost pressure is described as accelerating every documented failure mode on this engine, not just adding power. That said, the tuning ecosystem for this engine is mature and staged sensibly: Stage 1 software-only tunes are widely offered as comparatively safe, while Stage 3/4 turbo upgrades are explicitly paired with forged internals, upgraded fueling, and better cooling by reputable tuners rather than sold as simple bolt-ons. A car showing any tuning history should be checked especially carefully for whether the anti-surge valve recall was completed, since a tuned car built on an un-retrofitted turbo combines two compounding risk factors rather than one.
A catless downpipe is described as the standard, near-mandatory Stage 2 modification for this engine. Whether this matters for emissions compliance depends on market and production year: cars without a factory gasoline particulate filter (GPF), such as pre-GPF-era or certain export-market cars, make downpipe installation straightforward from a compliance standpoint, but later EU-market cars fitted with a GPF for emissions compliance would need this considered specifically, since a removed GPF is illegal for road use in the UK/EU and will fail an MOT/roadworthiness emissions inspection. Confirm whether the specific car in question was originally fitted with a GPF before assuming a catless downpipe carries no compliance risk.
This profile reflects consensus from a detailed specialist buyer's guide (ThreePiece.us, drawing on documented owner cases including a Belgian and a French forum account), tuner-published technical guides and product listings (YPG Motorsport, Weistec, RENNtech, MACHGRADE, Kinugawa, TunedMercedes), and TorqueCars' M133 tuning guide, not manufacturer-confirmed limits beyond the anti-surge valve recall itself, which was a genuine, Mercedes-acknowledged factory action. Treat any suspected tuned or previously tuned example as needing a full pre-purchase inspection specifically including turbo shaft play, confirmation the anti-surge recall was completed, a cold-start listen for chain tensioner noise, transmission temperature logs, and oil leak inspection near the wiring harness, rather than relying on an OBD scan alone.
Buying Advice
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 since 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, since 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 or AMG specialist before committing, including a physical look at the wiring harness, not just a code scan.
Community Sentiment
Mixed. Enthusiasts appreciate the M133's extraordinary performance credentials and tuning potential, but experienced owners consistently warn that this engine punishes neglect, aggressive tuning, and infrequent oil changes severely. The wiring harness oil issue has caused significant frustration given Mercedes' refusal to support owners outside warranty, and it comes up in nearly every long-term ownership thread.
Frequently Asked Questions
❯How reliable is the Mercedes A45 AMG M133?
The Mercedes A45 AMG M133 has a reliability score of 50/100, rated "RISKY". Fast thrills, expensive bills ahead
❯What are the common problems with the M133?
The most frequently reported issues are Oil Infiltration into Engine Wiring Harness, Fuel System Failures, Pump and Control Module, Turbocharger Wear and Anti-Surge Valve Issues, Thermal Management / Power Reduction in Hot Conditions, among others. See the Known Issues section above for symptoms, affected mileage, and repair costs.
❯Does the M133 have oil infiltration into engine wiring harness problems?
Yes, this is a documented issue on the M133, typically appearing around 60,000-150,000 km. 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. Typical repair cost: €1,500-4,000. DIY difficulty: Hard, harness replacement is labor intensive and connectors are tight to access.
❯Does the M133 have fuel system failures, pump and control module problems?
Yes, this is a documented issue on the M133, typically appearing around 50,000-120,000 km. 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. Typical repair cost: €600-2,000. DIY difficulty: Moderate, pump access is straightforward but wiring diagnosis takes time.
❯Does the M133 have turbocharger wear and anti-surge valve issues problems?
Yes, this is a documented issue on the M133, typically appearing around 80,000-160,000 km. 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. Typical repair cost: €1,200-3,500. DIY difficulty: Hard, turbo removal needed for thorough inspection or replacement.
❯Does the M133 have thermal management / power reduction in hot conditions problems?
Yes, this is a documented issue on the M133, typically appearing around 0-200,000 km. The M133 exhibits noticeable 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 rather than indicating a fault in most cases. Typical repair cost: €200-800. DIY difficulty: Easy, no repair needed, upgraded intercooler or oil cooler can mitigate.
❯Does the M133 have maf sensor and throttle body seal deterioration problems?
Yes, this is a documented issue on the M133, typically appearing around 60,000-130,000 km. 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. Typical repair cost: €150-600. DIY difficulty: Easy, both parts are bolt-on replacements.
❯Does the M133 have engine rebuild difficulty, proprietary sleeve design problems?
Yes, this is a documented issue on the M133, typically appearing around 150,000-250,000 km. 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. Typical repair cost: €3,000-8,000. DIY difficulty: Expert only, block work requires specialist machine shop involvement.
❯Is the M133 worth buying used?
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 since 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, since 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 or AMG specialist before committing, including a physical look at the wiring harness, not just a code scan.
❯Should I buy a Mercedes A45 AMG with the M133 engine?
Do not choose between the 360hp and 381hp M133 based on power alone. The facelift's higher output comes from a factory recalibration, not a weaker part, so it is not a red flag by itself. What matters more on both versions is documented oil change history at or below 10,000 km, physical confirmation the wiring harness is dry, and proof the car has never been run at boost levels above factory spec. A well maintained pre-facelift car is a safer buy than a neglected or tuned facelift car.
❯What should I check before buying a used M133?
Before buying, check: 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.
❯How many km will a M133 last?
There's no fixed mileage limit, it depends on maintenance. The parts worth budgeting for proactively are: Engine Wiring Harness (60,000 km), Borg Warner Turbocharger (100,000 km), Fuel Pump and Control Module (80,000 km), MAF Sensor (60,000 km). Engines that clear these checkpoints with documented maintenance commonly continue well beyond typical ownership periods.
❯How much does it cost to maintain a M133?
Estimated ownership cost is €6,000-12,000 over 3 years depending on mileage, condition, and whether major components such as the turbo or wiring harness require attention, based on known issues and typical service needs.
❯What is the real-world fuel consumption of the M133?
Owners report real-world fuel consumption of around 11 L/100km.
❯What oil should I use in a M133, and how often?
Community-reported real-world usage suggests changing oil every 10,000 km using MB 229.5 or 229.51, 5W-40 or 0W-40 fully synthetic, often more conservative than the official service schedule.
❯Is it safe to tune or remap the M133?
The M133 is commonly modified, with a high risk level when pushed beyond stock. Typical weak points under tuning: Turbocharger (anti-surge valve / bearing and shaft), Camshaft adjuster solenoids, Timing chain tensioner, DCT clutch. Emissions-delete modification is a known risk area on this engine.
❯What other cars use the M133 engine?
The M133 is also found in: Mercedes-AMG CLA45 (C117), Mercedes-AMG CLA45 Shooting Brake (X117), Mercedes-AMG GLA45 (X156).
❯Why does the M133 have a bad reputation?
Fast thrills, expensive bills ahead The biggest recurring complaint is Oil Infiltration into Engine Wiring Harness. Mixed. Enthusiasts appreciate the M133's extraordinary performance credentials and tuning potential, but experienced owners consistently warn that this engine punishes neglect, aggressive tuning, and infrequent oil changes severely. The wiring harness oil issue has caused significant frustration given Mercedes' refusal to support owners outside warranty, and it comes up in nearly every long-term ownership thread.