The Definitive Guide To The Mercedes-Benz M272 And M273 Engines - Common Failure Symptoms and Diagnosis

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When you think of a ten-year-old Mercedes, what's the first thing you imagine? For me, it's comfort and luxury, not high performance and reliability. But in reality, the M272 and M273 engines actually check all of the marks offering smooth operation and strong, reliable power. 

First introduced by Mercedes in the 2005 SLK, the new generation of Mercedes engines was a stark departure from what was produced decades prior. Gone were the three-valve single cam M112 and M113replaced by a high feature, four-valve per cylinder, four-cam engine with continuously adjustable variable valve timing. This new generation also featured the addition of a balance shaft. Because of these changes, these engines produced greater power with reduced noise and emissions compared to the preceding M112 and M113. The M272 and M273 could be found in all of the model classes (minus the Maybach) and was offered in 2.5, 3.0, 3.5, 4.7, and 5.5-liter variants.

In 2017, we campaigned an M272-equipped C300 in the AER series. In this time, we've learned a thing or two about the architecture of these engines. The only modification we made was the single stage composite manifold offered in the SLK. This wasn't mandatory, it was just more suitable for continuous high RPM operation that’s common in a racing environment. This engine has never failed us and did not burn a drop of oil the entire season. Since the M272/M273 has been in production for the last fifteen years or so, many of its common ailments are well documented and easy to reference.

FCP Euro Mercedes-Benz C300 AER

 

These are the most common issues you will run into with the M272/M273:
  • Secondary Air Injection Pump - The Mercedes ECU injects fresh air into the exhaust system on cold starts to aid in rapidly lighting off the catalytic converters. This air is injected by commanding an air pump and opening an air injection valve that feeds air into the injection points of the cylinder head. With age, these motors can become very loud during operation and are prone to failure. It’s recommended to replace both the pump and the relay at the same time.
  • Air Cleaner Sealing Ring- The air induction system is a well-engineered combination of components designed for both maximum unobstructed airflow and noise suppression. Within the air hoses is a nylon wire fabric used for noise suppression. It’s common for the fabric to separate from the plastic frame and cause obstructions. The air cleaner box features two air filters. Improper removal and installation of the air cleaner sealing ring can lead to codes indicating that the system is running rich, self-adaptation faults P0172, P0175, P0337, P0338, P0341 as well as a fluctuating idle at operating temperature.
  • Intake Manifold Swirl Flaps - Flap position is controlled by the ECU and is driven by a vacuum diaphragm mounted on the front of the intake manifold. The shaft position is monitored by hall-effect sensors mounted on the rear of the intake manifold. It's common for the shafts to fail due to a broken operating lever and set off fault codes P2004, P2005, P2006. We always recommend replacing the manifold assembly as we have seen instances of manifold flaps failing internally and breaking. These broken pieces can get sucked into the combustion chamber, damaging the valves or the cylinder.
  • Upstream Oxygen Sensors- Upstream oxygen sensors provide data that the ECU uses to determine many things. The correct ignition timing, fuel required for proper engine operation, converter heating, self-adaptation for idlethe list goes on. A rough idle, out of range self-adaptation values, and oxygen sensor codes are typical indicators that the sensors need to be replaced. Sensor performance diminishes with age, so we recommend replacement every hundred-thousand miles. Idle self-adaptation values above four percent are typically a cause for concern. Poor performing sensors will cause the ECM to shift fuel trim towards rich which causes spark plug fouling. It's good practice to replace the plugs at the same interval. As a reference, normal self-adaptation values range from -1.25- 1.25%.
  • Engine Thermostat - The single most common failure we see on the M272 and M273 is the map-controlled thermostat. This is an electronically controlled thermostat designed to regulate coolant temperature between 85 and 105 degrees Celsius. As such, temperature fluctuations are common with coolant temperature ranging from 80 to 95 degrees Celsius with a properly operating thermostat. We recommend thermostat replacement at the sixty thousand mile interval. The thermostat resistance specification is 15.2 ohms ± 1.5 ohms. If maintenance history is unknown, consider replacing the thermostat and radiator hose at the same time. Old hoses have a tendency to seal poorly at the O-ring connection. When the computer can no longer control the thermostat element, the common fault codes are P0599, P0598, and P0597. As for coolants, Genuine Mercedes Benz and Pentofrost NF can be used.
  • Upper Guide Pulley - Mounted on the water pump are two guide pulleys for the serpentine belt system. The upper grooved pulley experiences greater bearing wear than all other pulleys in the system. A high pitched cyclical noise during operation in high humidity or a grumbling RPM- dependent noise are typical indicators of excessive bearing wear. When the pulley fails, at a minimum, it will shred the belt. This leads to loss of all accessory drive components, such as the power steering pump, alternator, and water pump. Belt tensioners and idler pulleys should be replaced every sixty-thousand miles or immediately after purchasing the car if the maintenance history is unknown.
  • Oil Leaks - Compared to the outgoing M112 and M113 series engines, oil leaks are much less common and practically speaking, a non-issue. Valve cover leaks are basically unheard of; from the factory, they used sealant instead of the traditional gasket, and it's solid. One place you should look for leaking is at the electrical plugs for the camshaft adjuster magnets. They are known to leak through the electrical connector and oil will wick its way up the engine harness. Factory sacrificial pigtails are available to protect the main harness from damage.

    • Engine oil cooler seals will leak with age. The telltale sign of a coolant seal leak is a dirty belt tensioner, as oil seepage from the cooler mists onto the tensioner and the oil attracts dirt. Depending on which model car you drive, replacing the oil cooler seal on V6 applications, it might require removal of the power steering reservoir.

    • Another potential leak is at the engine oil separator. It has a plastic cover sealed by a rubber O-ring that becomes brittle and loses its effectiveness over time. Look for oil residue on the retainer screws of the cover to determine if the cover is leaking. These retainer screws are Torx on older engines and external Torx on the later variants. In extreme failure cases, oil will fall on the exhaust manifold, and when it burns off, you will smell it in the cabin. If you smell oil, you should assume the covers are leaking. 
  • Balance Shaft and Idler Gear Sprocket - Many early production (2004-2008) M272 and 273 engines were manufactured with balance shafts or in the case of M273 engines an idler gear sprocket that would get eroded aggressively by the timing chain. This would cause the engines to fall mechanically out of time, would produce cam and crank timing correlation codes and extremely rough running. The most common fault codes related to this are P0059, P0060, P0064, P0272, P0275, and P0276. The factory codes are typically 1200 and 1208. Verifying that the engine is mechanically in time requires removal of the 4 camshaft sensors and placing the engine at 305 degrees. You will be able to see the part number stamps in the windows. If it is determined that the engine requires a balance shaft, it is an engine out service and our repair kits can be found at this link

That should cover everything you need to make a decision whether or not you want to get into one of the many awesome Mercedes with the M272/M273. So far with our AER C300, we have been pleasantly surprised by the reliability and overall performance (other than shearing wheel studs off mid corner during a race). If you want to see our C300 and other Mercedes content, make sure to check back in and subscribe to our YouTube channel. 

 

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