4Matic is a common all-wheel-drive system that was developed and patented by Mercedes. However, since this system is used on many Mercedes cars, it can cause numerous problems. In this blog, we’ve outlined the most common issues. We explain how you can identify them and how to fix them. Read on!
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1. Problem With The Viscous Couplings In The Transfer Case
This is a significant problem arising in the 4matic system on the Mercedes vehicles. Since the 4matic system causes a variation in speed between the rear and front axle, this often leads to the problem with the viscous couplings.
Usually, the viscous couplings on the 4matic system last about 60,000 to 75,000 miles. But, once it becomes faulty, it should be replaced soon. Some signs of failed or defective viscous couplings include – a rough ride on tight turns, shuddering, and, at worst, the drivetrain can lock up completely.
Moreover, the actual sign of failure usually occurs once the vicious couplings get too aggressive and start coming on too hard and too much. If this happens, then it implies that the components in your 4matic transmission are struggling with each other to work correctly. To learn more about viscous couplings, watch the video below.
The most common symptom that will help you know that your viscous coupling is too aggressive is when you make tight turns after highway driving. In that case, you would notice that your Mercedes seems to want to stop as if you had put the brakes on. In simple words, the vehicle will hate tight turns.
Furthermore, there can be a bucking and binding sensation while driving if the steering is turned all the way to its limits. Besides, there can often be a slight scrubbing of tires, which might indicate a problem in the 4matic system on your Mercedes.
Testing For Problems
There is also another test that will help in identifying any problem with the viscous couplings. To perform this test, you first have to put the vehicle in two-by-four mode. Then jack the vehicle’s rear end up in the air via a rolling jack. Next, slowly let the clutch out in first or low gear.
Subsequently, after a few tries, you will notice that you can let the clutch out with the engine running while the viscous couplings let enough slop allowing the wheels to stay still at one end of the car without overriding the two-by-four. At the same time, the engine powers the wheels at the other end of your Mercedes.
You should perform the above test after highway driving for about 25 miles or so.
If you fail this test, you must consider replacing the viscous coupling immediately to avoid damaging your 4matic transmission. Note that your viscous coupling is working fine if you pass this test once out of many tries. Additionally, if you fail four times in a row and then pass the test, you are also OK.
If the viscous coupling on your Mercedes is faulty, you should replace it with a new one. Or else you would have to remove the center driveshaft from the vehicle to disengage the four-wheel drive. If you choose to do this, you can drive your car in two-wheel drive for years without needing to replace the viscous coupling or harming any other vital components.
However, it is not recommended to disengage the center driveshaft. Instead, it would help if you consider replacing the viscous coupling.
2. Problem With The 4Matic Shifter
Another problem that occurs with the 4matic transmission on the Mercedes is the shifter getting stuck. When this happens, your car will start just fine, but the car won’t shift when you move the shifter into drive. This is because the shifter hesitates to move and is stuck.
Most Mercedes cars with the automatic 4matic transmission have a gear selector shifter interlock safety feature. This safety feature locks the gear shifter in park when the engine is turned off. While, if you need to move and turn the gear shifter into drive, you must insert the key and turn it to position I or II.
This interlock mechanism allows the shifter to move out of the park if both these conditions are met –
- The brake pedal is pressed
- Turn ignition to spot I, II, or run
If the shifter on your Mercedes gets stuck or does not move out of park. Then any of the following can be the culprit –
- Low voltage or dead battery
- Defective shift interlock solenoid
- Spilled liquid on the shifter assembly
- Defective brake light switch
- Loose shift rod or a broken transmission shift cable
- Faulty ECU (engine control unit) or TCU (transmission control unit)
Suppose you suspect a problem with the shifter in your Mercedes. Then firstly you should check the battery for any fault. Once confirmed that the battery is working fine and is adequately charged. You should check for the two most common problems: a damaged shifter module or a defective brake light switch.
Brake Light Switch
The failure of the brake light switch is persistent in Mercedes vehicles. Moreover, it is the most common reason for transmission getting stuck in park problems. The shifter will not work unless the brake pedal works correctly, which Federal law requires.
Once the brake light switch becomes faulty, the shifter cannot know if the brake pedal is pressed or not. Therefore, the shifter will get stuck in park.
As a result, to confirm whether the brake light switch is working or not, you might want to check if the brake lights are operational. But this is not a good test to troubleshoot whether the brake light switch is working.
When the brake light switch fails and the car can’t get out of park, a common indication is that the ABS, ESP, or BAS light will also turn on. If this happens, then you should replace the brake light switch.
To replace the brake light switch on your own, you might have to consider buying a star Torx bit set costing around $20-$30. Also, a new brake light switch will come about $25-$30 in the United States. Next, follow these steps –
Locate The Brake Light Switch –
The brake light switch on your Mercedes is located above the brake pedal. Remove the underside panel cover to gain access to it. Usually, the panel would be held in place with 3 to 5 Torx head screws. So, you would need a Torx set for that. However, some older models might have Phillips screws, so check before buying a screwdriver set.
Remove The Panel –
Once you have removed the screws, you will have to pull down the cover to access the brake light switch. Remember that the cover won’t come out entirely in some models.
Remove The Brake Light Switch –
Once you have accessed the switch, remove it by pressing the locking tab and rotating it clockwise.
Install The New Switch –
Once you have removed the faulty brake light switch, unplug all the wirings from it. Next, connect wires with the new switch and install it by twisting it in a counter-clockwise direction.
Gear Shifter Assembly
The shifter module (gear shifter assembly) can fail on the Mercedes due to internal failure or wear. Shift interlock solenoids located inside the shifter assembly often fail or quit working. Moreover, plastic parts of the shifter can break over time.
If the gear shifter assembly is at fault, you must manually get the vehicle out of park until the part is replaced.
An easy way to detect the problem with the shifter module is to look at the gear selector on the instrument cluster and check if it displays the correct shifter position. If not, then the shifter module is bad and needs to be replaced to ensure proper working.
The ignition switch must be in positions I, II, or engine running for the shifter to work. Once the key is at any of these positions, the shifter gets unlocked from park via an electronic switch or cable. If the switch or cable is not working correctly, the shifter might get stuck in park.
A faulty or dead battery is the most common reason for the shifter to get stuck and not come out of park. If the battery on your Mercedes is bad, it needs to be replaced to ensure proper working of the shifter and other vehicle’s essential components.
3. Transmission Goes Into Limp Mode
Another common problem is the 4matic transmission in the Mercedes vehicle going into limp mode.
To solve this problem, you can try –
- Pulling your car over and turning it off
- Remove the key and don’t press any buttons or the gas pedal
- Wait for about 20 seconds
- Start the vehicle and drive to see if it is out of the limp mode
If following the above steps doesn’t help your car to come out of the limp mode, then there might be underlying problems that you should address. If ignored, your Mercedes will go into limp mode more frequently.
To diagnose any underlying problem, check the following –
Transmission Fluid Level
Verify that the fluid level is optimal. It is the most common and least expensive issue that could lead your transmission into limp mode. Fluid leakage issues on high mileage vehicles often lead to a low transmission fluid level. If the fluid level is below the limit, the 4matic transmission will go into limp mode.
To check the level of transmission fluid, take the help of a dipstick which is readily available for about $20.
Transmission Control Unit (TCU) Fault Codes
When the Mercedes 4matic goes into limp mode, it stores fault codes in the vehicle’s computer. Specific code related to the transmission system is stored in the TCU (transmission control unit). In comparison, generic codes like P0705 are kept in the ECU (engine control unit).
You can check the fault codes yourself by using an OBD II scanner.
13 Pin Connecter Adapter Plug And O-Ring
If you detect fault codes pointing to communication problems with the valve body, gear ratios, or similar issues. Then instead of spending hugely on a new valve body, check the 13-pin connector adapter plug and replace the O-rings. The O-ring plug usually leaks and disturbs the connection between the valve body and the TCU.
Replacing the O-ring is easy and can be done at home. Once replaced, use an OBD II scanner to erase all the fault codes.
If after replacing the O rings, the problem with the car going into limp mode remains, and the diagnostic scanner points in the direction of the valve body. Then you might have to consider replacing it.
The valve body is located inside the 4matic transmission, and the transmission does not need to be removed to replace the valve body. The total replacement cost of changing the valve body is around $500-$1000 in the United States.