Common Problems Mercedes-Benz 2006 to 2013 W221

The S-Class is the Mercedes-Benz flagship model and, without a doubt, a masterpiece. The S-Class W221 chassis was manufactured from 2006 until 2013.

Even though it is such a complex luxury sedan, it is one of the most reliable S-class Mercedes-Benz in the last few decades. That doesn’t mean that the S-Class W221 has no issues. This article discusses the most common problems that affect models such as S350, S550, and S400 Hybrid.

Common Problems

1. Auxiliary Battery

The W221 S-Class has two batteries. The main battery starts the engine, but the second auxiliary battery runs various electronics. Because the W221 has an electronic transmission shifter, it also puts the vehicle in Park if the main battery fails.

Like any battery, the auxiliary battery needs to be replaced. The auxiliary battery mostly fails if the car is over seven years old or has over 100,000 miles. Replacing the auxiliary battery on a W221 is relatively easy and can be completed at home.

2. Air Suspension Compressor

The S-Class is equipped with air suspension. The air compressor is the heart of the air suspension. It is utilized to raise and lower the vehicle.

It often fails or might wear internally to the point of not generating enough pressure to raise the car. Once the air compressor fails, it causes the vehicle to drop to the ground, and the warning message “Stop Vehicle Too Low” displays on the dashboard.

The compressor is located behind the front bumper and passenger side. It can be easily replaced in about an hour. It used to be a costly repair, but the price of a W221 air compressor has decreased significantly; you can find a replacement W211 air suspension compressor for under $150 online. It is an easy job for any car owner with a few essential tools to complete in their driveway.

3. Transmission Electronics

Another common problem affecting the pre-facelift model (from 2007 to 2009) primarily concerns transmission electronics inside the 722.9 7-speed automatic transmissions. The transmission control unit (TCU), valve body, or conductor plate can fail, which sends the car into limp mode, and the transmission no longer shifts.

In the early days, the dealer was the only one who could replace the valve body. The valve body has the Transmission Control Unit (TCU) mounted. This means they are both located inside the transmission. In addition, the TCU requires coding.

Mercedes-Benz was refusing to sell these parts even to independent auto repair mechanics. Some companies specialize in reprogramming used TCUs, a service not offered by any Mercedes-Benz dealership.

Today, not only will the dealer sell the valve body to Independence repair shops, but you can also find third-party transmission experts capable of restoring your old TCU, valve body, and conductor plate. The right transmission expert can also program a used conductor plate to match your Mercedes-Benz VIN.

The pre-facelift W221 S600 was equipped with the 5-speed 722.6 transmission, as the 722.9 could not handle the torque of the V12 at the time.

4. Amplifier

The amplifier, located on the left side of the trunk, does all the heavy work of running the COMAND. S-Class COMAND uses a fiber optic loop to connect components such as the radio, navigation, and CD changers.

When the amplifier fails, you will have a radio that turns on but won’t hear any sound. Other problems caused by a lousy amplifier include the command not turning on or your battery drains when the vehicle is parked.

5. OM642 Diesel Engine

If you have an S-class with a diesel engine, such as the S350 BlueTech, with over 200,000 miles, you will likely start experiencing problems with the oil cooler, chain, swirl flaps, turbo actuator, EGR, and injectors, especially if the vehicle wasn’t maintained properly.

This engine is very popular in the European market. Very few S350 BlueTech models with diesel engines were sold in the US market.

6. Window Problems

It’s common to see a Mercedes Benz S-Class with a window that will not go up or down. The problem is usually the window regulator, but it can also be the module itself.

The window regulator is the mechanism that moves the window up and down. The window motor can also fail, but it is much less likely. To fix the window problem, you need to remove the door panel and replace the window regulator.

The door modules are the brains that control the window operation. They often fail due to corrosion or internal failure and must be replaced or updated.

To update the door module on a W221, you need an authorized Star Diagnostic scanner with an active Daimler login. This problem was common for models up to VIN# A161249.

7. Air Suspension Airbag

The S-Class suspension is overall more reliable than the suspension of the W220. It is not uncommon for air suspension airbags to fail. It is a repair that you should expect once the vehicle passes the 100,000-mile mark. It is most likely to happen sooner if you do many City driving or drive on poorly maintained roads. We often see S550 with over 150,000 miles and original air suspension airbags.

8. Rear Level Height  Sensor

The rear-level suspension sensor is above the rear axle and determines the vehicle’s height on the back. The sensor can fail, which causes the car to drop to the ground, again only at the back. It will affect both rear struts, unlike when you have a bad rear airbag that causes the car to drop at one corner.

It is an inexpensive repair, and many S-Class owners with DIY skills can fix it themselves. The challenge is accessing the rear-level sensor mounted above the rear axle.

9. Gear Selector Module

The S-Class no longer has a mechanical connection from the gear shifter to the transmission. It uses what is known as a shift by wire.

When you change the gear between PRND, the shifter module sends a signal to the transmission valve body, which controls the valve body. The Intelligent Servo Module (ISM) is responsible for this, and it can fail.

10. Inverter Converter Assembly: Hybrid Only

The high-voltage inverter converter is only found on the Mercedes-Benz S400 Hybrid. Unfortunately, it is a widespread problem affecting virtually all S400 vehicles as they age. Once the Inverter Converter fails, the S-Class no longer starts. The part is challenging and unavailable from aftermarket suppliers other than Chinese suppliers.

The Inverter Convert Assembly (Part number 540 44 50) costs between $2500 and $3000 at the dealership. The repair can range between $5000 and $6500 if you consider time and parts. Depending on how many miles the S400 Hybrid is on, fixing this problem can sometimes cost more than the car is worth.

11. A/C Blower Motor

The blower fan may fail, so your A/C and heat will stop working. The blower motor usually fails due to moisture. At first, the blower motor will work intermittently, turning on and off randomly. Eventually, the blower motor fails and will not turn on, leaving you with no air conditioner and heat.

When the blower fan starts intermittently, it is time to check the vehicle. Please don’t wait until it fails because it will happen when you least expect it. Replace the blower motor before it completely fails. Replacing the blower motor at the dealer costs between $650 and $900. It is not a complex repair; if you decide to replace it, plan for up to two hours.

Other possible problems that can affect the W221 include:

• Camshaft Adjuster Solenoid Can Fail
• Crankshaft Position Sensor Can Fail
• Driveshaft Flex Disc May Crack
• Auxiliary Battery

12. Seats

The front, optional, dynamic multi-contour seats look simple yet complex.

They contain numerous air bladders, valves, hoses for the air bladders, electronic control modules, Motors for seat adjusting fail for the seat ventilation, and seat heating pads. On top of that, there is also a separate external air pump for the bladders in the trunk. And what can go wrong? Well, mostly, the air bladders can leak somewhere. Then, occasionally, the electronic modules can be faulty, or they will only need a software update, and sometimes even the seat wiring can be damaged.

13. Drains

Sunroof drains can clog. There are four drains on the regular sunroof, but if you don’t want to remove the headliner, you can access only the front drains, so occasionally carefully clean them with some fish tape or edge trimmer line.

Conclusion

The most common problems with Mercedes-Benz S-Class W221 (S350, S400, S550) are the transmission valve body, air suspension compressor, suspension airbag, and amplifier. These repairs are generally expensive, ranging between $700 and $1500. If you have DIY skills in fixing these problems, the repair will cost you around $150 to $300. A well-maintained Mercedes-Benz W221 S-Class, especially the S550 4Matic, can be a pleasure to drive and is, overall, a very reliable vehicle.

The most reliable W221 is the 2008 to 2011 S550, equipped with the naturally aspired M273 engine and 7-speed automatic transmission. The 2010 to 2011 S550 is a great choice for an upgraded look. The 2012 S550 has a new twin-turbo engine. Even though this engine has a few issues, it is not expected to last as long as the M273 engine.

The W221 has no common significant problems requiring a complete engine or transmission overhaul. However, if you depend on a mechanic or Mercedes-Benz dealer for help, any problem with the S-Class will be expensive. If you don’t plan on maintaining the S-Class, an aftermarket vehicle warranty is worth considering.

Frequently Asked Questions

Is the Mercedes W221 S-Class reliable?

It can be with good maintenance, but it has many complex systems. Air suspension, electronics and battery related faults are the most common costly repairs.

What is the most common W221 problem?

Auxiliary battery warnings and Airmatic air suspension failures are among the most common issues owners report.

Why do so many W221 warnings appear at once?

The W221 relies on many networked modules. A weak main or auxiliary battery can trigger several unrelated warnings at the same time.

Check these troubleshooting and repair guides for more help on your Mercedes-Benz.

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