Limp mode is a security function for your engine and transmission. When the engine or transmission control unit has recognized a serious faulty parameter from the engine or transmission, the car will go into limp mode. The limp mode does often reduce the power and limit the RPM of the engine so you can drive your car to a workshop without damaging the engine.
For example, Your engine control unit is detecting that your turbo boost pressure is 2.0 bar when the maximum boost pressure should be 1.3 bar. Overboost may damage your pistons or other internal parts fast. Because many car owners do not take enough notice of the engine light, the engine control unit sets itself to limp mode and shuts off the turbo boost completely and puts a max RPM limit to 3000 RPM’s, to make sure that you won’t blow or damage any engine parts.
In the video below, you will get in-depth information about what limp mode is. The video is specific for truck diesel engines, but the video will give detailed information for all car models.
Limp Mode Symptoms
The purpose of the limp mode function is to get you to the workshop in the safest way without damaging any engine components on the way to the workshop. Different car manufacturers design different kinds of limp modes to save your engine. The common characteristics of limp mode may differ a bit, depending on the problem with your engine/transmission and depending on which car and engine you have.
Here are some of the most common symptoms when it comes to limp mode.
Reduced engine power / turbo boost shut off completely
RPM limit lowered
Your automatic transmission is “stuck” in a gear/limited to max 3rd gear
If you experience all of these symptoms, your car is for sure in limp mode and it has to get fixed as soon as possible.
Below, you will find the most common things that usually cause the limp home mode. As you see, I only mention the most general issues.
The reason for this is that limp mode could be caused by a lot of different engine components in your engine bay. Therefore, the solution for this is to read the trouble code memory with an OBD2 scanner to find the problem before you are replacing any engine parts!
When the engine control module, transmission control module or brake control unit (ABS) detects a problem in the engine, transmission or with the brake system, it will store a trouble code in your DTC memory.
If one of the control units decides that the problem is dangerous for the engine or transmission, it will put the car into limp mode. Therefore, limp mode could be caused by a lot of different things.
Because of this, every time when the limp mode is active, there will be a stored trouble code in the trouble code memory. Therefore, the best solution to fix the limp mode without replacing the wrong parts is to find out which this trouble code is.
When the limp mode is active, you should read the trouble code memory with an OBD2 scanner as soon as possible, to make sure that the trouble code won’t get self erased, which could cause delayed troubleshooting.
Things to Consider
When researching on the internet, you will get many tips on what could cause the limp mode. People are often telling you that they had the same characteristics in their vehicle five years ago. For example, “I replaced this part and it fixed my problem.”
The problem with the limp mode is that you can get the same characteristics with a lot of different faults. That’s why you should never listen to anyone that has had the same problem before. You will only end up wasting your money on parts that were not faulty in the first place.
It is straightforward to read the DTC memory with a good scanner and find out the real solution to why your car has gone into limp mode. You could either drive your car to a friend or a mechanic to get help to read your DTC memory; it will probably not cost much money, and you will get a real answer to your problem.
How to Use an OBD2 Code Scanner?
The process to connect an OBD2 scanner is pretty simple. First, you have to locate the OBD connector, generally found under your steering wheel. I recommend attaching a car battery charger while you are doing this job to avoid any damages to the electrical system.
Never connect an OBD2 scanner when you have a bad/worn out car battery. If you think you need a new car battery, you can check out the best ones in this article at ReviewJam.com. If your car battery is good and you have a car battery charger connected, turn the ignition on and follow the manual with the OBD2 scanner.
Where Can I Get an OBD2 Scanner?
One thing that we strongly recommend, is to purchase a good OBD2 scanner to read your trouble codes at home by yourself. There are a lot of cheaper scanners on the market that will do the job, and it could be an excellent investment instead of taking it to your mechanic all the time. Workshops usually charge 20-100$ to read the trouble codes from your car once, and because of this, you can save the scanner cost in just 1-2 workshop visits.
If you do not have an OBD2 scanner at home, you could either let a workshop read the trouble codes from your car or consider purchasing a scanner for your vehicle.
One OBD scanner that we often recommend to our readers, is the BlueDriver Bluetooth Scanner. It’s compatible with the most Smartphones on the market and it can read enhanced trouble codes from your vehicle. Just check the list of compatible vehicles to make sure your car model is listed before purchase.
If you have any trouble codes stored in your memory and you do not know which to fix first, you could save and erase them and take your car for a drive to see if the problem comes back or not. If you are fortunate, it was just a coincidence, and your car may work as it should. However, in most cases, the trouble code will come back, and it will need repairing.
When you have found out which error code is causing the limp mode, you should search for some information about the trouble-code and not just replace the part that it is telling you it is faulty.
Just because you got a trouble code on the throttle body, for example, it does not automatically mean that the part is faulty, it could also be a wiring or software issue.
The OBD2 scanners in our review have an inbuilt trouble code library where it will show you the causes and solutions of different trouble codes.
What to Do if Limp Home Mode Occurs On the Road
If the limp mode suddenly happens while you are driving the car far from home, make a safe stop as fast as possible to check for any leakage, smoke or noise from the engine or transmission. If everything seems okay, you could either drive to the closest workshop or get it towed if you feel uncomfortable. If that’s not possible, find the shortest way to your home and fix it there or get it towed to a workshop.
Towing your car to the workshop or home is always the safest move.
Limp Mode FAQ
My limp mode is intermittent, and it went after an engine restart?
The limp mode often dissapears after a restart of your vehicle. At the start of your engine, the engine control unit will check if all the sensors are okay. If the status is okay, the control unit will allow you to drive your car as usual.
The problem may not be occurring at idle, and that is why it will remove the limp mode automatically for you. Then when the control unit detects the fault again, it will put your car into limp mode again.
My Limp mode occurs when accelerating hard and is happening when driving normally?
If the problem only occurs when you are accelerating hard, there is most likely a problem with your boost control system. If the vehicle detects an overboost/underboost pressure, it will go into limp mode.
If you are getting into limp mode at a lower speed or at idle also, you are most likely not having a boost problem. However, you should always check your DTC memory before doing any repairs or troubleshooting.
Is it dangerous to drive with limp home mode?
Yes, the limp mode is set for a reason. If you notice that your car has gotten into limp mode, you should fix it as soon as possible. The limp mode is designed so you can drive the closest way to a workshop to get the problem fixed.
Do not drive around with the engine light ON. Even if you know the problem and it’s not a fault that will cause any damage, it can hurt your engine, and you will not notice if you get any real trouble with your engine.
I have replaced the damaged part; will the engine light and limp mode go away by itself?
Yes, in most cases. The trouble code system works in cycles. Each time you start your vehicle, and it gets hot, and it has tested all the sensors, it gets registered as one fully functional cycle. Depending on the car model, the engine light will reset after a fixed number of cycles. If it has detected that the fault has not occurred within 10-20 periods, it will see the problem as repaired.
However, the easiest way and the best way is of course to reset the engine light and trouble codes with an OBD2 scanner. With these tools, you can always check all the parameters in the engine to see if they are okay if you have some knowledge.
Don’t panic when the limp mode occurs. It’s designed to make your engine survive to make sure that you can drive to the workshop to repair the problem.
Limp mode is caused by an electrical problem with the engine or transmission.
Limp mode is a security function.
Make sure that you go to a workshop or try to fix it yourself as soon as possible. It’s not good to drive around with limp mode.
You can buy an obd2 scanner to check the cause of the limp mode yourself at home.
Do not just replace parts on your vehicle without reading the trouble code memory first.
If you have any more questions about the limp mode or want to tell us your story about it, you can comment down below. If you have any other car questions, you are welcome to read our other articles on our blog or ask us for free at our homepage. We will help you out as soon as possible.
Good luck with your troubleshooting and I hope that I will see you in the next article!
Hello I'm Magnus, the owner and the writer of this website. I have been working with cars since I was 16 and I'm specialized with in-depth Automotive diagnostics. Also been driving drifting for the last 6 years. I'm here to give you answers to all your automotive questions and I hope that you enjoy our content.