Mercedes-Benz C 300
Modern turbocharged four-cylinder with direct injection and piezo injectors. Successor to the M271. Less susceptible to timing chain issues. Good balance of power and economy.
C 300: Lively Without Excess
180 kW M274 in the W205 — brisk enough for spontaneous overtaking, refined enough for everyday use. A solid all-rounder.
Engine Weaknesses 6
The high-pressure fuel pump on the M274 is driven by a lobe on the intake camshaft. Wear on the drive lobe or pump follower leads to pressure drop.
Symptoms: Metallic ticking from engine area, starting problems or extended cranking, power loss, fault code P0087
On the M274 too, the camshaft adjuster solenoids develop leaks. Oil penetrates the wiring harness by capillary action and can damage the engine ECU.
Symptoms: Fault code P0010, CEL, oil traces at camshaft connectors, lambda sensor failure, in severe cases ECU failure
Primary weak point of the M274: the electric thermostat sits deep in the engine block and is hard to reach. Replacement takes around 3 hours.
Symptoms: Engine does not reach operating temperature or overheats, temperature fluctuations, fault codes P0597–P0599
The PCV valve on the M274 clogs or breaks. Fault code P052E. Parts are inexpensive (~€63), but installed hidden under the engine ECU.
Symptoms: Fault code P052E, CEL, power loss, fault returns immediately after clearing
The M274 petrol engine has two NOx sensors that frequently fail. Each sensor costs around €600 as a part; with both sensors the repair bill quickly reaches €1,500.
Symptoms: Check engine light, NOx sensor fault code, elevated exhaust values, possible limp mode
The M274 with direct injection and no port injection tends to carbon deposits on intake valves like all GDI engines. Walnut blasting every 60,000–80,000 km is recommended.
Symptoms: Stumble under partial load, rough idle, slight power loss
Vehicle Weaknesses 7
Longitudinal members, jack-point attachment holes and rear axle subframe rust through. MB offers goodwill replacement.
Polycarbonate blind cover of the panoramic roof incorrectly bonded. When opening, the blind can come loose. Recalled by MB.
Ball joints on the wheel-side wishbone and rubber-metal bushes wear. New suspension geometry makes repairs more involved.
Some W205 models discharge the battery unusually quickly during extended parking. Cause: elevated quiescent current draw from control units.
The W205 shows above-average front axle issues from the second MOT onwards according to TÜV statistics. Worn control arms and drop links are the main causes.
W205 A/C fails with 'Air conditioning off' without a fault code in the onboard computer. Often the compressor or A/C control unit is defective.
Panoramic roof on the W205 creaks when opening and closing. Guide linkage can bend and jam the roof. Repair often requires complete removal.