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Common Mercedes Problems
Oil Leaks
There are several possibilities for causes of an oil leak on your Mercedes. On older models, worn or incorrectly fastened oil pan gaskets can cause oil to leak through. For M272 or 273 engines, the plastic expansion plugs located on the back of the cylinder heads may need to replaced. If you notice oil leaking from the passenger side, you may need to tighten cambox covers to prevent oil from leaking onto the exhaust or manifolds. Loose transmission cooler line unions can also cause oil to leak onto the exhaust. Finally, failure of the PCV system in your Mercedes’ crankcase ventilation system may cause it to collect excess oil vapors and begin to leak.
Coolant leaks
Proper pressure in the cooling system is maintained by the radiator cap, and it should be checked first if you notice a coolant leak. If the radiator cap is working fine, an internal leak could be caused by a faulty cylinder block, cylinder head, or head gasket. It is common with Mercedes for the fitting to come off of the back of the driver’s side cylinder head where the heater hose is connected. If you notice coolant leaking externally from below the exhaust manifold, a blown head gasket is the likely cause.
Power steering leaks
Fluid leaks can often develop from the power steering rack, causing a lack of steering fluid and damage to the power steering pump. The seal on the front of the power steering pump, the power steering pressure line hose, and the steering box are also places to check for leaks. Signs of a steering fluid leak include a whining or squealing sound when you start to accelerate or when you turn the car and notice more stiff steering.
Check engine light
The first easy fix if your check engine light is on is to make sure the gas cap is tightened. If the gas cap is loose or cracked, the check engine light will stay on for extended periods of time. If the gas cap is intact and the light is on, you may be experiencing problems such as a blown head gasket, faulty fuel injector, faulty oxygen sensor, or cracked or loose hoses.
If the light is flashing, this indicates serious issues with the engine that should be tended to immediately.
Suspension concerns
(ie. Noises and leaks)
Noticing creaking noises and vibrations when going over bumps or hitting a pothole? The most common Mercedes suspension issues typically originate from the control and thrust arm bushings, because they endure the most force when braking, turning, or accelerating.
For manual suspension systems, check for binding on the sensors on each suspension arm, water damage, and wiring issues. For automatic systems, there could be a problem with the sensor for the suspension system module.
If your vehicle gives you the command, “Car is low, visit workshop,” there may be an air leak in the suspension system causing the car to rise but too slowly to adequately reach normal driving level. In this case, the shock absorbers and air hose connected to each shock should be examined.
Maintenance light/Service A service B due now
The first indication that your Mercedes is in need of service should come between 5,000 and 6,000 miles when your vehicle needs an inspection and tire rotation. Service light A is a wrench icon that will illuminate on your control panel, indicating that it’s time for a motor oil replacement, filter replacement, fluid checks, and other minor maintenance. When two wrenches are lit up, your vehicle is due for Service B, which includes inspection of the mechanical, electronic, and computer systems, the heating and cooling system, and the fuel lines and connectors.
To reset your service interval, press either of the top arrow buttons on the steering wheel until the FSS indicator appears. Then, press the R button on the instrument cluster for 2-4 seconds, and then press it again after the display reads “Do you want to reset service interval?”
Steering wheel shakes/pulsation while braking
A cracked flex disk, or guibo, is a likely cause of the shaking you feel when you brake or accelerate past certain speeds. The transmission shaft, drive shaft, and differential are all connected by the flex disk, and a faulty disk can result in abnormal driveshaft movement and vibration of the vehicle floor.
In addition, the joints at the front axles of your vehicle that control power and torque transfer from engine to wheel are prone to wear and can cause shaking with vehicle speed changes. Unbalanced wheels are another possible cause of steering wheel shakes at high speeds.
Window doesn't go up or down/crunching noise while moving windows
Quick Tip: Before taking your Mercedes to a dealer, pull up all four window tabs and hold them for about 10 seconds in order to reset the windows. This simple solution has solved issues for many owners.
If the above trick does not work, there is most likely a problem with your power window regulator. Issues with the power window regulator mechanism can cause the windows on your vehicle to refuse movement. An electrical problem with the window regulator can cause the window to roll up or down slower than it should, but before assuming the regulator is the issue, make sure the window switch itself is inspected, as this is also a likely cause of window failure. If you hear clicking or grinding when the window is rolled up or down debris may be trapped between the window and the motor assembly, which can cause the regulator to work harder than it should to move the window.
Electrical concerns
(ie. Battery keeps dying)
Often poor battery life is caused by parasitic drain caused by electrical components in your vehicle that continue drawing current after it is turned off. While some drain is normal (i.e. for the clock, radio, and security alarm), electric problems such as a faulty seat control module can result in too much battery drain when your vehicle is not running.
An alternator with a faulty diode that causes the circuit to charge even when the engine is off can also cause excessive battery drain.
Finally, a defective Control Unit or Controller Area Network Bus can also cause your Mercedes battery to die quickly.