2009 Mercedes-Benz C350 Problems

RepairPal has identified the most common problems with the 2009 Mercedes-Benz C350 as reported by actual vehicle owners. We'll tell you what the problem is and what it'll take to fix it.

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24
Known Problems

The Mercedes Benz C350 may have engine oil seeping or leaking from the back of the cylinder heads. This is commonly misdiagnosed as leaking valve covers.

On the back of the cylinder heads there are three, in total, plastic expansion plugs that plug access ports to the camshafts. These plugs are well known for seeping oil, and leaking if left unattended. The oil will run down the back of the engine and eventually make it to the ground. 

Replacement of these three plastic plugs is extremely simple, and should be done as regular maintenance. The recommended interval for replacement is every 60,000 miles.

The power steering reservoir designed for the Mercedes Benz C350 commonly leaks power steering fluid causing a screeching sound when turning the steering wheel, especially when the vehicle is stopped. The power steering light may illuminate on the dash for more severe leaks.

This is caused by cracking in the plastic reservoir, or a hardened, brittle seal between the power steering reservoir and power steering pump.

Remediation involves replacing the power steering fluid reservoir, power steering fluid, bleeding the system of air, and replacement of the seal between the reservoir and power steering pump.

When starting the engine after sitting for several hours, a knocking sound may be heard for several seconds. This is a common issue with the 2005-2010 Mercedes Benz C350. There are three common problems that can cause this sound to occur:

-Oil pressure building too slowly, allowing for movement between the crankshaft and crankshaft bearings

-Stretch or wear of timing chain and components

-Balance shaft (counter rotating shaft) gear wear

The remediation for these problems can be crankshaft bearing replacement with correct size, replacement of timing components, or balance shaft replacement.

Inside grab handles, the upholstery on the center console cover, and door trim panels can delaminate. Most commonly replacement of the affected part is necessary.

The camshaft adjuster solenoid (which is related to the variable valve timing system) may fail or timing chain/balance shaft components may wear, resulting in illumination of the Check Engine Light and various drivability issues. Mercedes-Benz has released a service bulletin outlining specific repair instructions depending on fault codes stored.

Failed spark plug wires and/or ignition coils can cause intermittent misfires (rough running); the Check Engine Light may also illuminate. Diagnoses of the ignition system will be necessary to determine which components are at fault.

The crankshaft position sensor may fail. Symptoms of this are: The engine will crank—but not start—especially when the engine is warm. The car may start again if it is left to cool off, but it may run roughly or have poor performance. Communicating these specific symptoms to your technician can save diagnostic time.

Catalytic converter failure is common and may cause a Check Engine Light to illuminate.

The mass air flow sensor tends to fail causing poor fuel economy and Check Engine light illumination. The engine air filter should be replaced when the mass air flow sensor is replaced; a dirty filter can allow debris to damage the new sensor.

Vehicles equipped with a 7-speed automatic transmission may develop a rough shifting condition, most commonly going up from first to second gear and going down from third to second or second to first gear. Our technicians tell us this is due to an internal component failure. Mercedes has released updated parts; the transmission will need to be removed and disassembled to complete the necessary repairs.

The heating, ventilation and AC (HVAC) heater box is susceptible to mildew buildup. This can result in a musty odor from the HVAC system, most noticeable when the system is first turned on.

A vibration felt through the center floor of the vehicle can be caused by driveshaft flex discs, which crack and shred, causing excessive driveshaft movement. Not repairing these can cause damage to the driveshaft center support bearing, or, in the worst case scenario, damage to the transmission or differential.

High mileage or older vehicles commonly develop leaks from the differential seals and/or cover. Our technicians recommend a complete reseal of the differential unit whenever these leaks are repaired.

The anti-lock brake system (ABS) modulator assembly may fail due to dirty brake fluid. Our technicians recommend a complete brake system flush every two years in order to help prevent this problem.

Due to the size and material used on the brakes of these vehicles, the brakes may start to squeak around the 50 percent wear point. The brake rotor surfaces become uneven, causing a lip to form at the outer edge of the rotor. Because of this, the rotors are usually replaced when the pads are worn (pad life varies depending on driving style and terrain).