What isLimp Mode?
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. It was designed this way 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 limp mode. When a Mercedes-Benz goes into limp mode, it only operates in second gear and reverses. You may feel a bang as transmission engages when you put it in gear. The first thing you should try is to check the transmission fluid level. The transmission has a dipstick tube but no dipstick in it. You will need this specialdipstick, though, to measure it correctly.
Top reasons causing Transmission To Go Into Limp Mode:
- Mass Air Flow Sensorcould also cause your transmission to go limp mode.
- Defectiveshift module inside the car.
- Bad Speed Sensor
- Brake Light Switch
- Defective transmission control module.
- Old Battery
These are the leading causes for limp mode, but limp mode could happen for other reasons which may not be directly related to the transmission.
How totroubleshootmycar that is notshifting?
-First, determine if the car is in limp mode or not moving. In limp mode, your car will drive in second gear.
– GetanOBD2/CAN scanner that readsand checks the engine/transmission codes. All car owners should own one, even if they don’t fix their cars. See our list of top recommended scanners here. You will get a fault code pointing you in the right direction. Write that code down, then go to our Mercedes-Benz customsearch to search all the Mercedes-Benz-related pages, forums, and websites in one place.
– If your fluid level is OK, then listenfor 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 as a bad torque converter, a bad transmission oil pump, and water contamination in the transmission.
Understanding Mercedes-Benz Transmissionsmodels.
– The5-speedtransmission was introduced around 1994 and was used up to 2007 models. This was a bulletproof transmission; you should be glad if your car had this transmission installed. This is designated as 722.6
– The7-speedtransmission was introduced in early 2000. It was first installed in some 2004 models. The 4matics were the last models changed from the 722.6 five-speed to the 722.9 seven-speed. This transmission is known as 722.9 or 7G.
To determine which transmission your car is equipped with, go to www.mercedesmedic.com/decode. Use one of 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 must find and repair the problem that caused the car to go into limp mode first. Once you do that, the car will sometimes go out of limp mode immediately. If the problem were more serious, after repairing the problem, you would need to reset the Transmission Control Unit complex codes. A generic OBD II scanner will not work; you will need an advanced scanner like the one mentioned above.
The shifter is stuck in the parking problem.
If your Mercedes Benz is stuck in Park and it won’t come out, then you could have a problem with the following:
– Shifter module. It 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 the park. After 2000 this is controlled by an electrical wire.
TIP: If this is your problem, look it up in the owner’s manual. A section should show you how to get the car out of the 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, the CLK-Class, and maybe others had defective radiators. The transmission fluid radiator is part of the coolant radiator in 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. You will need another transmission very soon otherwise.
Standard transmission OBD-II Codes.
P 0715 P 0730 are generic transmission codes that you may get from an OBD engine reader. On a Mercedes, generic Diagnostic Trouble Codes DTC codes point to the transmission speed sensor installed on the conductor plate. You can replace the conductor plate. It can be done with the transmission still in the car. You can get a conductor plate herefor less than $200.
IMPORTANT
If you have a defective shifter, in most models years 2000 and newer (with a few exceptions), you need a shifter model which 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
You can’t install a used shifter on 2000-up S-Class (W220), 2003-up E-Class (W211), and newer models.It needs to be a virgin shifter module and needs programming.
Regardless of the information, you must verify if your shifter module needs programming.
