Besides the odd defect from time to time, BMW transmissions are not known as being problematic. One common issue that appears with certain models, however, is that higher mileage vehicles will jerk suddenly whenever you brake. This problem is actually mentioned on CarComplaints.com as the second most common failure mode in BMW models fitted with ZF transmissions.
A BMW jerking when it stops is typically a symptom of a problem inside the transmission. The ZF mechatronics unit fitted to some BMW transmissions is notorious for downshifting from second to first gear. The most common cause is damaged or worn solenoids or solenoid springs in the valve body. DIY replacement of this part is possible, but a professional repair will cost up to $3,500.
Repairing this issue on your BMW is possible for owners skilled in error code analysis and repair of BMW transmissions. The DIY repair is rated as “Hard,” costing up to $2,000 and requiring two hours of work.
Luckily, this is not the only transmission-related issue that could be causing your BMW to jerk when you stop, and many of the other possibilities are simpler and cheaper to resolve. Let’s take a look at what the typical BMW ZF transmission problems are and how to address them.
Another common issue that is often reported by BMW owners is that their BMW is stuck in park, if you are having this problem, check out this article!
The Most Common BMW Transmission Problems
A jerky transmission may have some less serious causes that can be more easily rectified. The following are a few of the most common BMW transmission problems that could also be causing a jerky car and information on how they can be rectified.
1. Low Transmission Fluid Level
Low transmission fluid level may be caused by a leaking oil pan gasket or a leak at the transmission wiring harness plug. This problem has been found on some high milers and can easily be rectified by installing a replacement gasket, installing a plug seal, and refilling with fresh transmission fluid.
Low transmission fluid level can lead to hard shifting of the gears and may lead to the vehicle shuddering and going into limp mode.
It is important to keep in mind that it is recommended to change your transmission fluid every 60,000 miles. BMW used to claim that its transmission fluid was “lifetime”. You will notice that there is no transmission dipstick on a BMW because BMW uses sealed transmissions.
The idea is that this prevents contamination, however, it has been proven time and time again that sealed transmission fluid still degrades overtime.
2. Defective Mechatronic Unit
The solenoids in the valve body controlling the gear shifting can wear out over time, or the solenoid springs may lose their compression leading to poor shifting, especially between first and second gear.
The vehicle will usually indicate error messages on the instrument panel. Replacing the transmission fluid may help dissolve any built-up sludge in the transmission that may cause the solenoids to be sluggish; if this does not fix the problem, the solenoids and solenoid springs may need to be replaced.
The parts cost for this replacement is several hundred dollars, what really gets you here is the labor involved. If you find that you will need this replacement done, you can check out this DIY video for some helpful tips.
Below is a pretty good video of the problem. The valve body is located inside of the transmission.
3. A Weakly Charged Battery
A weakly charged battery has also resulted in gear shifting problems or the transmission getting stuck in gear. Check the battery voltage and recharge the battery to see if the problems persist. Check that the alternator is working and able to recharge the battery.
A faulty alternator regulator can lead to the battery not charging back up to an optimal state of charge to power the electronic functions in the vehicle.
Be aware though that this is a pretty rare occurrence on the scale of most likely causes of a jerking car. One of my old BMW E36s jerked pretty significantly upon acceleration when the battery was dying. But the battery was so fried that the vehicle only made it a few yards before the engine died.
4. Faulty MAF Sensors
Faulty MAF sensors can cause a car to shudder and jerk at low revolutions per minute. The Mass Air Flow (MAF) sensor measures the airflow to the ignition system and relays this to the electronic control unit (ECU).
Unfortunately, MAFs can be quite finicky and once the sensor had been coated in dust, pollen, or whatever other contaminant is in the air, it will start causing a number of different problematic symptoms.
Luckily, MAFs are one of the easiest problematic parts to address on a BMW. It sits at the front of the engine bay and is right underneath the hood. You can get some MAF cleaner from your local auto parts store and spray the sensor with it.
Diagnosing The Root Cause Of The Jerking BMW
You will need a BMW Scan Tool to read the error codes from the ECU and the transmission control unit. The ECU will force the vehicle into limp mode when it detects a damaged transmission. While unlikely, if your BMW is in “transport mode” it can also display some odd symptoms.
If you’re interested in picking up a BMW Scan Tool, by far my favorite is the Foxwell NT510. I love it because it features a lot of the same functionality that you would expect in a $500+ scan tool, but for less than $200.
In limp mode, the vehicle will be locked into second gear and will only be able to be driven very slowly to a safe point for inspection and repair. Some of the common BMW transmission error codes observed are:
- Transmission stuck in gear
- BMW Transmission slipping
- Transmission shifting hard
- Transmission malfunction drive moderately message
- The engine revolutions increase, but the transmission fails to shift
- Shift lag between first to second and second to third
- Gear ratio fault codes
- Fluid leak on the ground
- Shifting gears is delayed
- Rough shifting between second and third gear
- Transmission service due
If the BMW transmission is stuck in limp mode, check that the battery is fully charged. Switch the car off for at least one minute before restarting to reset the error message in the ECU.
To determine the exact cause of what is causing transmission trouble, plug the BMW Scan Tool into the OBD2 port and analyze the fault codes. It is likely to be one of the following:
Transmission Mechatronic Sleeve Defective
The mechatronic sleeve is where the harness from the Transmission Control Unit (TCU) connects to the transmission. Unplug the harness and check it for oil contamination on the connectors; this may cause poor communication between the TCU and the mechatronic valve body. The oil seal on the sleeve connector can be replaced from underneath the car.
Mechatronic Bridge Seal Adapter Defective
The BMW Scan Tool could indicate a Transmission Fault on the iDrive screen if the mechatronic adapter is cracked (Part #: 0501 215 783 01); also known as a trans-seal grommet.
The trans-seal grommet allows the fluid to flow from the transmission to the mechatronic valve body without any fluid loss, allowing the oil pressure in the mechatronic to perform normal gear shifts. The plastic grommet can become brittle over time and cause a leak.
The loss of operating pressure will result in the solenoid valves not opening and closing correctly, resulting in erratic shifting and shuddering of the engine. The replacement grommet is available in plastic or aluminum and can be easily replaced by DIY enthusiasts.
This error is common on these BMW transmissions: 6HP26, 6HP28, and 6HP32. Aluminum Part Number SFC-MA-001 is available from online part stores. The BMW models most affected by this problem are:
- 2001 to 2008 BMW E65/E66 7 Series
- 2004 to 2006 BMW E53 X5 V8
- 2003 to 2010 BMW E60 5 Series
- 2005 to 2011 BMW E90 3 Series
- 2003 to 2010 BMW E63/E64 6 Series
- 2007 to 2013 BMW E70 X5 Except 4.0d
- 2008 to 2012 BMW F01/02 7 Series
Mechatronic – Valve Body Defective
Some BMW ZF mechatronic units are known for problems in shifting down from second to first gear. Consider replacing the solenoids in the valve body first, remembering to change the foam strip between the solenoid terminals and the connectors.
Remanufactured mechatronic units are also available for fitment and can be purchased online. Someone can replace the unit with moderate DIY skills, but you will have to ensure that the new unit is coded to your VIN (Vehicle Identification Number) by the part seller or BMW dealer.
A qualified mechanic would typically charge you between $1,500 and $3,500 for a mechatronic unit replacement and coding. BMW dealers charge between $2,100 and $3,500 for this repair and issue a warranty on the work done. With such a slight difference, I recommend that you have the repair done at a BMW dealership.
If you are still having issues with your BMW or perhaps the symptoms are a little bit different, you can check out this article if your BMW is vibrating.
References:
https://www.youcanic.com/wiki/bmw-transmission-problems-explained
https://www.e90post.com/forums/showthread.php?t=1443603
https://www.bimmerfest.com/threads/jerk-coming-to-a-stop.936059/#
https://www.delphiautoparts.com/gbr/en/resource-center/making-sense-your-sensors-maf-sensor