Coolant Line to Turbo Metal Line O Ring Mercedes Blue Tech 350

What is Limp Mode?

Known as the limp / fail safe / emergency mode is when your transmission is stuck in one gear and doesn't shift. In this condition, you only get speeds up to 30 mph max.

Why does this happen?

When the sensor input values from the different sensors inside the transmission, in the valve body, MAF sensor and other parameters are outside the normal operation range, the car could go into the limp mode, go home mode. The reason it was designed this way is to protect the transmission from further damage. Don't panic! Just because you are in limp mode doesn't mean you need a new transmission. You may also get a check engine light if your transmission goes into limp mode. When a Mercedes-Benz goes into limp mode, it only operates in second gear and reverse only. When you put it in gear, you may also feel a bang as transmission engages. The first thing you should try is to check the transmission fluid level. The transmission has a dipstick tube but with no dipstick in it.  You will need this special dipstick though to measure it correctly.

Top reasons causing Transmission To Go Into Limp Mode:

• Mass Air Flow Sensor could also cause your transmission to go into limp mode.
• Defective shift module,  inside the car.
•  Bad Speed Sensor
• Brake Light Switch
• Defective transmission control module.
• Old Battery

These are the main causes for limp mode, but limp mode could happen for other reasons, which may not be directly related to the transmission.

How to troubleshoot my car that is not shifting?

-First, determine if the car is in limp mode or if it is not moving at all. In limp mode, your car will drive in second gear.

– Get an OBD2/CAN scanner that also reads transmission codes and check the engine/transmission codes. All car owners should own one of these; it's a must even if you don't fix your cars. See our list of top recommended scanners here. You will get a fault code which will point you in the right direction. Write that code down, then go to our Mercedes-Benz custom search to search all the Mercedes Benz related pages, forums and website in one place.

– If your fluid level is OK, then listen for a whine. Do you hear one? Make sure to check the fluid level first and add if necessary. If the level is correct and you hear a whine, you may have serious transmission problems.  That means the fluid is not circulating in the transmission. This could be due to several issues such  bad a torque converter, bad transmission oil pump, water contamination in transmission.

Understanding  Mercedes-Benz Transmissions models.

– The5-speed transmission was introduced around 1994 and was used up to 2007 models. This was a bullet proof transmission, and you should be glad if your car has this transmission installed. This is designated as 722.6

– The7-speed transmission was introduced in early 2000. It was first installed in some 2004 models. The 4matics were the last models that were changed from the 722.6 five-speed to the 722.9 seven speed. This transmission is known as 722.9 or 7G.

To find out which transmission your car is equipped with go to www.mercedesmedic.com/decode Use one the decoding options in that link to see the transmission code. It will say if you have a 722.6 (5 speed) or a 722.9 (7 speed).

How to get the car out of Limp Mode?

You need to find and repair the problem that caused the car to go into limp mode first. Once you do that, in some cases the car will go out of limp mode right away. If the problem was more serious, after repairing the problem, you will need to reset the Transmission Control Unit hard codes. A generic OBD II scanner will not work; you will either need a Star DAS Xentry scanner or an advanced scanner such as the ones we mentioned above or similar.

Shifter stuck in park problem.

If your Mercedes Benz is stuck in Park and it won't come out then you could have a problem with:

– Shifter module. Could be defective.
– Brake Light Switch
– The connection between the ignition module and the shifter module. Some of the older models had cable used to unlock the car from park. After 2000 this is controlled by an electrical wire.

TIP: If this is your problem, look up in the owners manual. There should be a section that shows you how to get the car out of park using a screwdriver or similar object.

If you don't have a manual download it here: Mercedesmedic.com/ownersmanual/

The car will not move at all, when in Drive or Reverse.

Do you hear a whine? In that case, you may have serious transmission problems.  Some of the E-Classes and the CLK-Class and maybe other models had defective radiators. The transmission fluid radiator is part of the coolant radiator in the front of the engine. Even though the coolant and the transmission are running in the same radiator to be cooled they have separate chambers. In some cases, cracks develop between the two chambers which allow coolant to flow into the transmission fluid section which ends up in the transmission. The glycol entering the transmission will destroy it. This is happening primarily in cars with Valeo radiators.  If you had this problem and replaced the transmission, you MUST replace the radiator as well. You will need another transmission very soon otherwise.

Common transmission OBD-II Codes.

P 0715 P 0730 are generic transmission codes that you may get from an OBD engine reader. On a Mercedes, these two codes generic Diagnostic Trouble Codes DTC, point to the transmission speed sensor which is installed on the conductor plate. You can just replace the conductor plate. Can be done with the transmission still in the car. You can get a conductor plate here for less than $200.

IMPORTANT

If you have a defective shifter, most model years 2000 and newer (with a few exceptions) you need a shifter model wich is "virgin" or new. The shifter module will need to be programmed to match the VIN of your car. The only exceptions when a used shifter may work are Mercedes model year 2000 and older plus:

• W210/W208  up to 2003
• R170 SLK up to 2004
• W163 up to 2004

On models including 2000-up S-Class (such as W220), 2003-up E-Class (such as W211) and newer models you can't install a used shifter.It needs to be virgin shifter module and needs programming.

Regardless of the information provided here, you are responsible for verifying if your shifter module needs programming.

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Source: https://www.mercedesmedic.com/mercedes-transmission-problems-limp-mode-no-shifting-troubleshooting-tips/