The very thought of an owner’s BMW going into limp mode is enough to drive fear into most drivers hearts. One minute you are driving down the road enjoying the wonderful Spring weather, the next minute there’s a loud “BEEP”, three lights flash on your dash and suddenly your car will not go over 3,000 RPMs.
What is limp mode anyway and is it really something to freak out about? What causes limp mode and what can you do about it if it happens to you? Read through this article to find out the answers to these questions regarding BMW limp mode.
What is Limp Mode?
It’s a known fact that modern day cars are virtually giant mobile computers with wheels. Nearly every system in your vehicle is controlled by a computer including the transmission, throttle, fuel injection, fuel mixture and many more. Sensors send signals to the various computers telling the car how it is operating. The computer system operates on a pre-determined range established by BMW.
So what happens when a sensor sends a signal that is below or above that pre-determined range? The car may go into emergency operation, otherwise known as “limp mode”. The idea is that if your car has entered limp mode that means that somewhere there is something wrong with the car and the computer is limiting the vehicle’s performance to prevent further damage.
Limp mode is a preventive measure, designed to allow a driver to allow a driver to finish his/her drive home and not be left on the side of the road. The signs that your vehicle has gone into limp mode are that the vehicle will not go over 2,500 or 3,000 RPMs, harsh idle, and the signs on the dash will light up like Christmas.
What Causes Limp Mode?
There are a variety of issues that can cause a BMW to go into limp mode. Some are significantly more serious and common than other issues.
Some of the most common causes of BMW limp mode, especially on newer models, are:
BMW N54 Charge Pipe: The charge pipe is only found on turbocharged BMWs. It connects the intercooler to the throttle body. The charge pipe handles all the compressed air that goes into the engine. The pipe is exposed to a lot of stress due to the heat of the engine bay and the incoming air, and unfortunately it is made out of plastic. If the pipe develops a crack the ECU will instantly go into limp mode and the pipe will have to be replaced. Luckily the charge pipe is not very difficult to replace, although it will likely set you back a few hundred bucks for the part.
BMW E90 M3 Throttle Actuator: The throttle actuators on the M3 S65 engines are prone to failure. There are two throttle actuators, one for each bank, and when one of them goes out it will throw the BMW into limp mode. The throttle actuator is not to difficult to replace, however, the part alone costs upwards of $500.
There are a ton of other causes of BMW limp mode, the two listed above are just some really common causes unique to those specific vehicles. Other common causes include: mass air flow sensor, automatic transmission issues, camshaft position sensor, crankshaft position sensor, throttle position sensor, and wiring issues.
As you can see, some limp mode causes are significantly less expensive and troublesome than others. A serious example of a sensor failure causing limp mode occurred on my BMW E36. One day I was driving my E36 out of the driveway during my morning commute to work and I noticed a sudden loss of power. My check engine light flashed, the car would not go beyond 3000 rpms, and the car would not shift gears. After checking the check engine light and scanning the ECU I realized that the camshaft position sensor had failed. Luckily the vehicle DID go into limp mode because driving a BMW with a bad camshaft position sensor can serious engine failure.
What Can You Do About It?
Unfortunately BMW limp mode sometimes gets a bad reputation from skeptics that think that it’s just another BMW gimmick to force BMW owners to the dealership. This contributes to the ongoing false narrative that BMWs are unreliable. This could not be any further from the truth. You should take limp mode seriously regardless whether you think your BMW has a serious problem or not.
The first thing you should do if your BMW goes into limp mode is drive the car straight home and park it. Do not take a chance with your BMW’s welfare and continue driving the vehicle around town. If you have a BMW scan tool or just a regular OBD 2 scanner you should check what codes come up. Hopefully that will narrow down the list of likely suspect causes.
If you do not feel comfortable with performing the diagnosis and repair yourself have the car TOWED to a BMW dealership or a quality indy mechanic. Another consideration is that depending on what caused the limp mode you may or may not be able to reset the mode after you have completed the repair. If it’s the case that you can’t reset the limp mode you will have to give the car to the dealer even AFTER you complete the repair!
Limp mode sucks whether you are driving a BMW or any other car. There are a few issues and symptoms that are unique to BMW limp mode, but besides that limp mode is pretty much the same across the board. The biggest thing is to take limp mode seriously as soon as it emerges, and have the vehicle diagnosed and repaired quickly.