BMWs have a lot of great features, they have refined interiors, precise handling, and great engines that produce buckets of torque. Unfortunately, BMWs also tend to be extremely expensive to repair when something inevitably goes wrong. One issue that has been common in the past among some model BMWs is a no-reverse problem.
The cause of a failure of a BMW to reverse will vary depending on the model BMW and transmission. Some of the most likely causes of a failure to reverse include (i) broken gear selector valve, (ii) mechatronics valve body, (iii) Reverse Drum, and (iv) the Reverse Solenoid. Luckily, many of these issues can be fixed within several hours by a DIY mechanic with the correct tool kit.
Over the years, BMWs have developed a mystique about them, that they are so complex and the engineering is so advanced, that the average DIY home mechanic cannot work on them without the aid of a significant amount of expensive equipment. This mindset earns the dealerships a lot of extra money, but it is frequently inaccurate. The reality is that in the case of a no-reverse problem, a DIYer can typically fix this problem within several hours and save an enormous amount on labor costs.
Why Some BMWs Don’t Reverse.
The GM6L45 Transmission No Reverse Problem
Some BMW models manufactured between 2007 and 2012 used a General Motors transmission designated GM6L45. The E90 3 Series BMW used this transmission, as well as the 1 Series and BMW X1 SUV.
The GM6L45 transmission is a 6-speed automatic transmission produced by General Motors.
The transmission was optimized for rear-wheel drive and all-wheel drive vehicles and was designed to handle engines that produced up to 332 ft-lb (450 NM) of torque for vehicles weighing up to 5,000 lb (2,268 kg).
When paired with a General Motors vehicle, the same transmission was designated GM6L50 and was used in the following GM cars;
- 2007 Cadillac STS-V, Cadillac STS, Cadillac SRX, and Cadillac CTS
- 2009 Holden VE Commodore, Holden VE Berlina, Holden VE Calais, Chevrolet Lumina, and Holden WM Statesman
- 2009 Cadillac Caprice, Chevrolet Caprice, and Daewoo Veritas
- 2009 Chevrolet Camaro.
All these model vehicles experienced the same reversing problem.
What Causes the No Reverse Problem in the GM6L45?
The most likely cause of the no reverse problem in the GM6L45 transmission lies with the gear selector valve which sits inside the transmission and connects to the mechatronics valve unit. The mechatronics valve body is an electronic valve body installed on the underside of the transmission and it controls the functions of the automatic transmission.
When reverse gear is selected, valves in the mechatronics body change the pressure, which moves the gear selector valve and activates the reverse gear.
If the gear selector valve fails, the transmission will not be able to go in reverse.
The gear selector valve fails because it is a two-part piece. One part is plastic and one part is metal and the plastic becomes brittle and breaks away from the metal rod, it is certainly the weak link in the transmission.
Dealers may diagnose that the entire gearbox needs to be replaced, however, you can easily replace the valve shaft while the gearbox and the mechatronic unit are in place.
Symptoms of a Faulty Gear Selector Valve
When the BMW is started, and the driver selects reverse gear, other than NOT going backward, the car correctly performs all of the below actions:
- The shifter indicates that the gearbox is in reverse gear.
- The external mirrors will dip into the reversing position.
- The reversing lights will switch on.
- You will also notice that no error codes are being displayed in connection with the transmission.
- All of the forward gears work as they should.
While the car has accepted the reverse gear selection, the reverse cog has not been actuated.
If the gear selector valve has broken, the hydraulic valves will operate and attempt to select reverse gear, but the gear selector valve is broken and will not move the actuators.
How to Replace the Gear Selector Valve
Despite what official BMW dealerships may tell you, the transmission does NOT need to be replaced if only the gear selector valve is bad, and you are not in for a potential bill enormous transmission replacement bill.
Whether you choose to do the work yourself or take the BMW to a reputable independent shop, replacing the gear selector valve is an exercise you can complete in under four hours.
- Jack the car up.
- Remove the plastic protection cover under the transmission.
- Drain the transmission fluid.
- Remove the oil pan.
- You will now see the mechatronics unit exposed.
- Check the condition of the selector rod (also known as the valve shaft.)
- Select park on the gear shifter and slide both ends of the broken gear selector valve out of the transmission.
- Remove the mechatronic valve body unit by undoing five of the six inverted torque bolts.
- The sixth bolt should be loosened but not removed on the front right side (looking forward).
- It will allow you to lower the mechatronic unit down slightly, which will give you enough angle to slide the new valve shaft in.
- Slide the new unit back in.
- Tighten the six inverted torqued bolts
- Undo the black plastic selector housing to create a sufficiently large angle to connect the other side of the selector valve.
- Connect the other side of the selector valve and retighten the housing bolts.
- Replace the oil pan.
- Ensure that the car is perfectly level before refilling the new transmission fluid.
Below is a great DIY video on replacing the gear selector valve, you can also check out this video for a brief synopsis on the gear selector valve issue.
The reverse gear should now be able to be selected.
The BMW E46 No Reverse Problem
The BMW E46 was an excellent 3 Series generation. I have owned several E46s and I did not have any complaints. No car is perfect, however, and one common problem that you will find on all of the E46 forums is the no reverse issue that was a common fault in all E46 automatic transmissions.
If you own a BMW E46 and it is suffering a no reverse problem, the first thing to do is to identify whether you have a GM or ZF built transmission. The surefire way to do this is by getting underneath the vehicle and taking a look at the green tag which will be in close proximity to the fill plug.
Identifying which transmission you have is not just important to ensure that you purchase the correct part, but it is also an important step in identifying the cause of the no reverse.
BMW E46 ZF Transmission No Reverse
The automatic ZF transmission is unfortunately a significantly more problematic no reverse issue than the GM. By far the most common cause is that the Reverse Drum (D-G Clutch Drum) will prematurely fail.
The issue here is that the snap ring that retains the reverse clutch inside of the Reverse Drum will snap and this will result in an inability of the Reverse Drum to engage properly. One good tell-tale sign of a Reverse Drum failure is if you open up the transmission pan you will find pieces of the snap ring in the pan.
Unfortunately, replacing the Reverse Drum is a significant job and will require removing the transmission from the vehicle. Independent mechanics will typically charge at least $3,000 to perform this repair and many BMW owners simply opt to swap out the transmission.
BMW E46 GM Transmission No Reverse
The automatic GM transmission is a significantly more mild fix and can be repaired by most DIY mechanics within several hours. The most common problem with the GM transmissions is the Reverse Solenoid.
The Reverse Solenoid is located inside the transmission and plugs into the valve body. The solenoid has a small filter screen inside of it which clogs up over time and will prevent the solenoid from regulating the pressure from the reverse gear. When this happens, the vehicle will fail to reverse.
The Reverse Solenoid is located at the front of the valve body and it will not require transmission removal in order to repair. If you opt to do it yourself, be aware that the part will cost somewhere in the neighborhood of $250-$300.
Other Possible Causes Of A No Reverse Problem
We have now covered three of the most problematic no reverse transmission problems found in several models. However, those are not the only issues that could be causing your transmission not to go in reverse. Let’s take a look at some of the other potential causes of a BMW no reverse problem.
The Transmission Fluid Level Can Cause A BMW Not to Reverse
The mechatronic valve system uses pressurized hydraulic fluid to change the gears.
If there is insufficient transmission fluid, it may not be producing sufficient pressure to activate the system. While this would affect the selection of all gears, and the automatic transmission would not change them, it is still worthwhile to check the transmission fluid level.
BMW claims that their transmissions are “lifetime fluid” transmissions. This means that you should never have to change the fluid in your transmission unless something has gone seriously wrong.
Unfortunately, this could not be further from the truth and after every 100,000 miles or so you should change the transmission fluid.
A Bad Valve Body Can Cause A BMW Not To Reverse
The valve body is not the most difficult part to replace in a BMW as it sits just inside the transmission, above the transmission oil pan. The valve body is not a specific fail point on any single BMW model, but all valve bodies will eventually become sluggish and fail overtime. The valve body is made up of many valve and passageways, and is connected to a number of sensors.
Symptoms of a Failing BMW valve body:
- Harsh and slow shifting between gears.
- Knocking sounds coming from underneath the vehicle when the car shifts gears.
- Warning light on dashboard indicating a transmission problem.
Check out a pretty good video on replacing a BMW transmission valve body here.
Certainly not the best look for ZF and GM to produce transmissions with significant inherent weaknesses that can and will frequently cause premature reverse gear failure in many models. Luckily, you now have the information to effectively identify the cause of your no reverse problem and determine whether you would like to have a mechanic perform the repair or whether you want to do it yourself. Remember, that most of the time you will not need an entirely new transmission when you have a no reverse problem and many of these repairs can be completed within several hours.