Mercedes-Benz C300 W205

This is one of the most common and well-documented M274 failures. The crankcase ventilation system consists of an upper PCV valve and a lower air/oil separator. Both components tend to fail, typically between 60,000 and 120,000 km. Symptoms include check engine light with code P052E, rough idle, oil consumption increase, and sometimes oil leaks. The lower component requires approximately 4-5 hours of labor due to poor accessibility, which drives up the repair cost. Mercedes dealer repairs run €1,500-2,000 including parts and labor. Independent specialists can perform the repair for €800-1,200. Some owners have experienced this failure multiple times. There is no official recall, though it affects a large number of M274-equipped vehicles.

Early M274 engines (primarily 2015-2017 production) were manufactured with wrist pins that had excessive tolerance. This causes a knocking or clattering noise, particularly when the engine is cold. In severe cases, the piston can crack, leading to catastrophic engine failure with white smoke and loss of power. NHTSA investigated this issue but did not issue a formal recall. Mercedes addressed the problem in production from approximately April 2016 onward with revised wrist pin specifications. Not all early engines are affected, but if you hear persistent cold-start knocking that doesn't resolve within a few seconds, have the engine inspected immediately. Repair involves short block replacement at €5,000-8,000 or used engine installation at €3,000-5,000.

The M274 camshaft adjusters can develop faults from around 60,000 km onward. Symptoms include a sharp tapping noise on cold start, erratic idle, and check engine light. The problem is often progressive - initially appearing only on cold starts and gradually worsening. Both intake and exhaust adjusters can be affected. Parts cost approximately €400-600 for the adjusters, with 5 hours of labor required. Total repair at a dealer is typically €1,800-2,500, while independent specialists charge €1,200-1,800. Some shops recommend replacing the timing chain simultaneously, which increases the total cost but addresses two related concerns at once.

The M274 uses a dual-row timing chain that is improved over the notoriously problematic M271 chain. However, the tensioner can still lose pressure over time, causing the chain to rattle on cold starts for a few seconds. This typically appears between 80,000 and 120,000 km. While less catastrophic than the M271 issue, ignoring a stretched chain risks chain skip and potential valve contact. Mercedes recommends inspection at 100,000 km. Replacement cost including chain, guides, tensioner, and sprockets is €1,200-2,200 depending on whether you use a dealer (higher) or independent specialist (lower). The M274 chain issues are far less frequent than on the M271, but still worth monitoring.

The IHI turbocharger on the M274 uses an electronic wastegate actuator that can stick due to carbon buildup, particularly on cars driven gently or mostly on short trips. Symptoms include check engine light, loss of power, limp mode, and sometimes a rattling sound from the turbo area. If only the actuator is faulty, replacement is relatively inexpensive at €300-600 including labor - the part itself costs €100-200 and the job takes about an hour. However, if the turbo internals are damaged from running with a stuck wastegate, full turbo replacement costs €1,200-1,500 at an independent shop. Regular spirited driving helps prevent carbon buildup on the wastegate.

Mercedes considers oil consumption of up to 0.5 litres per 1,000 km as normal for the M274 engine. Consumption typically increases after 40,000-60,000 km. Many owners report burning 1 litre per 2,000 km, which exceeds the normal threshold. Causes include worn piston rings, valve stem seals, or PCV system failures. If consumption is excessive (more than 1L per 1,500 km), a compression test and borescope inspection are recommended. Valve stem seal replacement costs approximately €1,500-2,000, while piston ring replacement requires engine disassembly at €2,500-3,000. Monitoring oil level between services is essential on M274 engines.

Mercedes recalled approximately 270,000 W205 C-Class vehicles with M274 engines produced between March 2014 and February 2018. Diode failures in the generator rectifier can cause a short circuit from the battery through the generator, potentially leading to generator overheating and fire risk, particularly during extended idling. The recall remedy involves updating the engine control unit software with an optimized generator control strategy. This is a free recall repair - verify with a Mercedes dealer using your VIN that it has been completed. If not yet done, avoid extended idling until the software update is applied.