For safety, allow some time before getting under the hood. The fan can run for up to about 5 minutes at a PWM setting of 40% after key-off to help cool the engine, but if battery voltage sinks too low, this can be suppressed. If a problem is detected, the fan is commanded to maximum speed. The reason these values are not 0% and 100%, respectively, is to allow for diagnosis: PWM values below 10% or above 90% should never be seen, and if they are, there is a fault somewhere. Using a Pulse-Width-Modulated (PWM) signal, the fan speed can be varied from off (10% PWM) to full speed (90% PWM). The Power Train Control Unit controls the electric cooling fan. This allows for fine-tuning of the warm-up process while still allowing coolant to flow to the cabin heating system, as well as careful regulation of the coolant temperature to a range of 98☌ to 108☌. Within the thermostat is a wax element that, when heated, adjusts the position of a rotary ball valve. The coolant thermostat contains a heating element, activated by a ground signal from ME, which is used to control engine temperature via the thermostat. The wax element moves the valve in response to heating from element R48, which is controlled by the ME-SFI unit. The coolant thermostat has a rotary slide valve (48b) to control coolant flow. After a cold start, ME switches off the coolant pump switchover ball valve via a vacuum actuator, stopping coolant flow. This allows the engine to reach operating temperature more quickly, which is intended to reduce exhaust emissions while improving heating performance. The ME-SFI engine control unit (ME) closely regulates the coolant temperature in the engine. The oil pump is driven by a separate chain from the crankshaft. Two overhead camshafts, each with solenoid adjusters and driven by a conventional timing chain, actuate a total of four valves for each cylinder. The crankcase and oil pans are made of die-cast aluminum with an open-deck crankcase, with high-strength aluminum alloy cylinder heads. The cooling and oil circuits are carefully regulated and controlled for better efficiency. The single turbocharger is vacuum-controlled. A high-pressure fuel pump delivers up to 200 Bar (nearly 3,000 psi) and is driven mechanically by the intake camshaft. The DI system uses Piezoelectric fuel injectors for extremely fast and precise fuel delivery. In the United States, the M274 is a 2 liter engine, but other displacement variants are found elsewhere. Intake air and engine thermal management are especially new systems, and the ECO Start/Stop function is standard equipment. Improvements in CO2 emissions, power, torque and engine noise were the goals for the design of this M271 replacement. The M274 is a gasoline direct-injection (DI) engine equipped with a single turbocharger. While not as widely installed as the big brother M276 and M278 engines, there are still millions of these engines on the road worldwide, many of them needing to visit your shop for maintenance and service. While our focus will be on the longitudinally-mounted M274 intended for rear-wheel-drive vehicles, the transverse-mounted M270 is essentially the same engine, and much of this information applies to both. Introduced to the United States in the Model 205 C-Class in Model Year 2015, the M274 4-cylinder engine joined its year-old sister engine M270.
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