Did your car suddenly become really slow when accelerating, and at the same time, it seems like it will not rev above 2500-3000 RPM while the engine light is flashing on your dashboard?
Then your car is most likely in a condition called Limp Mode. Why does this happen, and how expensive will it be to repair my car?
In this article, we will go through what limp mode is, the most common symptoms, causes, and how to fix it.
What is Limp Mode?
Limp mode is a security function for your engine and transmission. When the engine or transmission control unit receives a very faulty parameter from the engine or transmission, the car will go into limp mode.
The limp home mode often reduces the power and limits the engine’s RPM to drive your car to a workshop without damaging the engine.
For example, if the engine control unit detects 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 very fast, and therefore, the ECU limits the engine power.
Many car owners do not take enough notice of the engine light, and therefore the engine computer sets itself to limp mode, shuts off the turbo boost completely, and puts a max RPM limit to 3000 RPMs to be sure that you won’t blow or damage any engine parts.
Limp Mode Symptoms
The most common symptoms of limp mode are check engine light, reduced engine power, RPM limit, or stuck gear.
Here is a more detailed list of the most common symptoms:
1. Check Engine Light
The check engine light is probably the first thing you will notice on your dashboard when the car is in limp mode. You can often experience this light together with an EPC light or a similar one. Here is a more detailed list of the most common symptoms of limp mode:
If the check light is on your dashboard, it is definitely time to check the trouble codes with an OBD2 scanner.
A check engine light can show up because of hundreds of different symptoms so therefore you can’t just guess the issue, you have to diagnose the check engine light properly with an OBD2 scanner.
2. Reduced engine power
This safety mode helps you protect your engine from further damage when it notices something is wrong with the engine.
To prevent more serious damages to your engine, the limp mode will reduce the engine power heavily and, usually obliterate the turbo pressure.
3. RPM limit lowered
Another safety feature that your engine control unit uses when setting your car into limp mode is lowering the RPM limit heavily. It is definitely in Limp home mode if you realize that it is impossible to rev over 3000 RPM in your car.
4. Stuck in Gear
If you have an automatic transmission, your car might limit the gear shiftings on your car, depending on your car model. It often happens, the transmission won’t shift over gear 3 for your engine’s future safety.
As you may understand, if the RPM limit is at 3000 RPM and your transmission is not shifting above gear 3, you can’t drive very fast.
If you notice all these symptoms at once, there is no doubt that your car is in limp mode.
What Causes Limp mode?
The most common causes of limp mode are boost leaks, overboost, faulty engine sensors, transmission issues, or wiring issues.
Here is a more detailed list of the most common causes.
1. Engine boost control problems
The most common cause of limp mode is boost-control problems. This can be a boost leak or, more likely, overboost. Overboost can happen if you have a turbo car, and it is quite critical to your engine, and therefore the engine control unit will limit the engine power because of this.
Common things that can cause overboost are a faulty wastegate, broken wastegate hose, boost control valve, or a faulty boost pressure sensor.
2. Faulty engine sensors
Another common cause is faulty engine sensors. The engine has many sensors that can cause your car going into this mode, so it is not easy to find out which one. Do not worry; later in the article, I will show you how you can diagnose it properly.
Common engine sensors that can result in limp mode are MAF sensor, engine temperature sensor, boost pressure sensor, or O2 sensor.
3. Transmission Issues
If you have an automatic transmission, the transmission control module can actually set the car into limp mode if something is wrong with the transmission. This can often be a faulty sensor, faulty valve, low transmission fluid level, or a bad shift solenoid.
4. Wiring Issues
Wiring issues to the engine or the transmission are also pretty common when it comes to this mode. It can be a broken wire or just corrosion at a connection.
For example, it can be broken wire to a boost pressure sensor, so the engine control will not control it properly. It can also be a missing boost pressure signal, making the engine control unit not take any risks and set limp mode.
How to fix limp mode?
Fixing this mode often requires a full diagnosis to prevent just replacing parts and washing money down the drain.
However, there are some easy and mostly free things you can try at home to try. It is not sure that it will make any difference, but you have nothing to lose by it either!
1. Check All fluids
Start by checking all fluid levels in your car. These include the engine oil, coolant, power steering, transmission, and brake fluid level. The significant one is the transmission fluid if you have an automatic transmission.
Make sure that these fluids are in good shape and if you can see anything strange with them. If you have not replaced them in a while, it is maybe time for a fluid change.
2. Clean MAF Sensor
The MAF sensor controls the air-fuel mixture in your car, and it can often become dirty, especially if you have an open-air filter. Dust and dirt on the MAF sensor will often cause it to send wrong values to the engine control unit, which may result in limp mode.
Remove it and carefully clean the sensor with an electronic cleaner. Remember that the sensor is susceptible, and you should not touch it with your hands.
3. Check & Clean or Replace Air Filter
The air filter makes sure that the engine always gets clean air without dust or dirt. If you have not replaced the air filter in a while, it can be so clogged that it will cause problems with the intake air.
The air filter is often easily located and often easy to clean. If it is filthy, it is probably time to replace it, though.
4. Check Trouble Codes
If you checked everything above without results, there is nothing more to do than make a proper diagnosis not waste your money.
To make a proper diagnosis, you need an OBD2 scanner to check the trouble codes stored in your engine control unit.
To fulfill a proper diagnosis, keep reading to the next section, where I show you how to diagnose it.
Limp Mode Diagnosis
The limp mode can be caused by many things. This means we cannot just replace things and hope for the best of luck. To diagnose limp home mode easily, you may also need some tools. If you do not have these, you can either borrow them from someone or let a mechanic workshop diagnose the car.
- Connect an OBD2 scanner and check the trouble codes. When limp home mode occurs, there is always a trouble code stored in the engine control module or the transmission control module. Continue the troubleshooting with the given trouble code you will get. You can find a lot of trouble code information articles on our sites also for more information.
- Check the boost pressure sensor with your diagnostic tool in live data – make sure it gives realistic values at idle or ignition. Replace if faulty.
- Use a vacuum or pressure gauge to test the wastegate and make sure it moves freely. Use your diagnostic tool to test the boost control sensor by testing it while putting pressure or vacuum on the wastegate. Replace the sensor or replace the wastegate if faulty.
- Check for intake leaks with an EVAP smoke machine. Repair any possible leaks or replace a faulty PCV valve .
- Check the MAF sensor values, O2 sensors, engine coolant temperature sensor, throttle position sensor, and air temperature sensor. Replace if faulty.
How do you fix limp mode?
The easiest way to fix this mode is to check what is going on in your car with an OBD2 scanner. If it just happened, you can try to remove and insert the car key to restart the car to see if it fixes the limp situation.
Can I drive my car in limp mode?
The limp mode should not be ignored. If you notice that your car has gotten into this mode, fix it as soon as possible. This mode is designed so you can drive the closest way to a workshop to fix the problem.
Don’t drive around with this unnecessary.
How many miles can you drive in limp mode?
There is no fixed amount of miles or km you can drive with limp mode. I do not recommend driving more than to the repair workshop when it appears.
Can a bad battery cause limp mode?
A bad car battery can absolutely cause limp mode. Low voltage can create many strange problems with your car’s electronic computers, and this mode is one issue.
How much does it cost to fix limp mode?
The limp mode can be caused by many vehicle problems, which also means it can cause many repair costs. Usually, you can expect a repair cost of 50$ to 500$, but sometimes it can be way more expensive if you are unlucky.
Can low engine oil cause limp mode?
Low engine oil does not cause limp mode just by itself. However, low engine oil can create low oil pressure, which can cause the hydraulic lifters to get empty on oil or the camshaft chain tensioner. This can, in return, cause this mode.
Can bad spark plugs cause limp mode?
Bad spark plugs will most often cause misfires, and misfires will trigger the check engine light. You will just experience a check engine light in most vehicles when the misfires occur. However, in some car models, you may experience limp mode because of misfires.
Can you Bypass Limp mode?
There is not really a way to bypass limp mode other than repairing the issue. In some cases, you can reprogram the car to remove the damaged sensor from the system if possible, but it is not a recommended way to do it. The best way is always to repair the issue.