BMWs are great cars to own, but when they start acting up out of nowhere, it can be scary. Most people don’t know much about cars, so when their car suddenly slows down and the dreaded “check engine light” comes on, they won’t know what’s going on. Don’t worry too much, because there’s a simple way to explain your car.
What Is Limp Mode on A BMW?
People sometimes call it “limp home mode.”
Limp mode on a BMW is supposed to be a safety feature that turns on when the transmission control unit or the engine senses a problem.
Either of these systems will put the car into limp mode, which will make less important parts of the car less useful, like the air conditioner, the speed of the car, etc.
The limp mode makes sure that less power is wasted on non-essential features and that the problem doesn’t get worse. In everyday language, it lets the car “limp home,” or in this case, to a repair shop.
It’s supposed to let the driver know that something is wrong and that they need to pay attention right away.
The limp mode is supposed to take care of things on its own to keep the engine from getting worse. If the owner doesn’t do anything when the “check engine light” comes on, the car will take more drastic steps and turn off important functions, including those that can affect the engine.
For example, it will turn off the turbo boost if it’s higher than the required 1.3 bar and lower the RPM limit to 3000 RPM to protect the engine.
How Long Can You Drive in Limp Mode?
Even though you can drive your car while it’s in limp mode, it’s not a good idea. It is made so that you can drive to the nearest auto repair shop to get the problem fixed.
If there are clear signs that your car is in limp mode, fixing it will save you money that would have been spent on fixing badly broken parts.
Don’t try to drive in limp mode if:
The engine is getting too hot.
Light for oil is on
Light for temperature is on
The check-engine light is on.
The engine or transmission is making noise.
There is also no set distance that a car can go in limp mode. This will depend on things like how well your car is running. Right now, you should worry about how far it is to your mechanic.
Read on to find out everything about limp mode, including what causes it, what its signs are, and how to fix it.
Signs That Your BMW Is in Limp Mode
These are the things you should look for to tell if your car is in limp mode. An expert can tell you where the problem is, but most people should let the experts do the diagnosing.
1. Check Engine Light
This is one of the easiest ways to know there is a problem because it is right there on your dashboard. Your EPC light or a similar one might come on at the same time as your check engine light.
But this light can come on for a very long list of things. So, the limp mode goes one step further and turns off the part that might be broken.
You can check the trouble codes and find out what they mean with an OBD2 scanner. This will help you figure out what might be wrong so you can fix it.
2. Reduced Engine Power
The only reason for limp mode is to keep the engine safe. So, it will try to make the engine work as little as possible by cutting power to parts that don’t need it.
3. Lowered RPM limit
When the limp mode is on, the computer will lower the RPM limit to 3000 RPM or less. Usually, this is paired with slow driving speeds of 35–45 mph.
4. Stuck in Lower Gears
In a car with an automatic transmission, the computer will stop you from changing gears if there is a problem. Most of the time, the transmission will keep the gear below 3 to protect the engine from getting any worse.
When the gear is below 3 and the RPM is only allowed to go up to 3000, it means you are driving very slowly. This shows that the limp mode is on and that something is wrong.
Common Causes For Limp Mode
1. Transmission Problem
When the car’s computer system has a logical problem, it goes into limp mode. This can happen if a sensor sends a signal value to the computer that is different from what it was programmed to send.
The computer will think that the sensor is broken because of this. The computer will then switch to its secondary programming, which will protect the transmission from more damage and send out another error signal.
2. Error in the Boost Deviation
If the turbo boost is just a little bit outside of the recommended range, the computer will flash the check engine light. This is a warning that there may be a mechanical problem that needs your help.
Some problems with boost control are a boost leak or too much boost. Overboost happens when a boost control valve, wastegate, wastegate hose, or boost pressure sensor is broken or not working right.
Check with an OBD2 scanner to see if any “soft codes” are listed. With these codes, you can find out if a low priority sensor is broken and needs to be fixed.
3. Battery Acid Leaks and Wiring Problems
When the acid in the battery leaks, it hurts more than just the battery. The acid eats away at the wiring, causing it to break. This makes it hard for the sensors to send signals to the computer.
Once the computer stops getting signals from the engine, which means it can’t talk to it, it will think there is a big problem with the transmission system.
Other things that can cause limp mode are:
Transmission valve body
boosts too much or not enough (Turbo engines)
Faulty engine sensors
Wire harness with damage
Link to the ground
Battery voltage is low
ABS or Brake system issues
Wheel speed sensor
Manifold absolute pressure (MAP) sensor
Sensor for the throttle position (TPS)
The engine got too hot.
The ECU needs to be set up.
Blown fuse for important parts of the car
If water gets into an engine sensor, like when you wash your car.
How To Bypass Limp Mode?
Even though you should take your car to a mechanic right away, there are three ways to get out of limp mode. You can try to reprogram your car’s computer to turn off the limp mode with these tips.
Stop in a safe place before you do anything else!
1. Check and Top Off Fluids
First, check your fluids while your car is sitting on a flat surface. To check the transmission fluid, put your car in park and turn the engine on. If it’s low, it could be what put the car into limp mode.
Take note of how the transmission fluid smells and what colour it is. If it’s burned or dirty, you’ll have to get a new one. If not, add the right amount of fluid and turn off the engine.
2. Shut Off Engine and Restart
Next, you must reset the ECU of the car. Wait 5 minutes after you turn off the engine. Check the levels of the other fluids, like engine oil, water, etc., and add more of what’s low.
This short break could be what the computer needs to reset itself and get out of limp mode.
3. Clear Check Engine Light
Third, you could unplug both of the battery cables and hold them together for 15 to 30 seconds. This is a manual way to get rid of any leftover power that was being used to store engine problem codes for the computer. If you do this, the computer will “forget” about the codes once they are cleared.
You can also use an OBD2 scanner to get rid of the codes. It will do the same thing faster and safer than doing it by hand.
Can Limp Mode Be Fixed?
Yes. You can fix the limp mode. Depending on what caused the limp mode in the first place, though, the cost of fixing it can range from $50 to $500 or even more in extreme cases. You can also do it yourself, which will save you some money but can only be done by a professional.
Fix the problem instead of trying to get around limp mode, which can be hard and sometimes doesn’t work. You do this by using the OBD/OBD2 scanner to read the codes stored in the car’s computer. With these codes, you can find out exactly what parts are broken so you can replace them.
The codes from the OBD/OBD2 scanner might help you figure out what’s wrong, but keep in mind that even small problems, like broken wires, can throw off the reading. This means that even if you replace a part, the check engine light will still be on.
Have a multimeter with you so you can check how well the wires conduct electricity. If electricity is flowing but not reaching the sensor, then you have to replace the wire.