Have you ever been driving and suddenly your car lost power and wouldn’t accelerate past a certain speed? Chances are that your car has gone into limp mode.
This is a serious warning, and you most likely have a serious problem inside your vehicle. Keep reading to learn about the causes of limp mode, symptoms to look for, and how to bypass limp mode if the situation calls for it.
What is Limp Mode?
Limp mode is a self-protect feature most vehicles are equipped with. When your vehicle gets abnormal readings from its sensors or detects an improper operation of a mechanical part, your car will engage this mode.
Limp mode or “limp home mode” is designed to protect the engine and transmission from catastrophic damage. Most diesel vehicles have a similar mode called “engine derate”.
Your vehicle will run very poorly, purposely put on you to protect you from major damage, but allowing you to “limp” the car home, to a nearby auto repair shop, or possibly even pulling over on a shoulder for the tow truck to be called.
When limp mode is engaged, it is telling you there is a serious problem with your vehicle, and you need to stop and understand why limp mode is engaged. Your first mission is to find a safe area to park and understand what caused limp mode to be triggered.
3 Signs of Limp Mode
#1. Limited Speed and RPM Limitations.
With limp mode activated, your car will show some of the following. Limp mode limits the power of your engine and transmission.
When in limp mode, RPMs may be limited (usually below 3,000), and your driving speed will usually be limited to about 35 to 45 MPH, or just not able to shift above a certain gear for being stuck in a limit.
#2. Poor Performance.
In limp mode, acceleration will be slow, and you may even feel your engine shuddering or misfiring.
You may notice that the transmission will automatically downshift, and it may have limited ability to shift above a certain gear (let’s say from 3rd, or maybe it won’t shift at all!).
Your vehicle has a limp mode and will have a limited speed and limited power, but it will show some abnormal behavior.
#3. Check Engine Light.
The check engine light will be on or blinking, and then if you have an overheating failure, you may also see this.
If the vehicle is overheating, you have no choice but to pull over immediately off the road until the vehicle is cooled down so you do not damage the engine and/or transmission any further, maybe be above normal tolerances.
And while to can move the vehicle again, you still put the vehicle into limp mode.
Then, plugging into an OBD2 scan tool will show you any of these faults that caused limp mode in the form of the fault’s diagnostic trouble codes. Most likely, the code will be a P2106, which represents the limp mode condition itself.
4 Common Causes of Limp Mode
Although limp mode can be caused by a variety of problems, there are a few easy-to-spot common causes.
#1. Low Fluid Level.
Low fluid levels, especially transmission fluid and oil, can cause a vehicle to go into limp mode.
This is especially true of the transmission fluid, since low fluid can create low pressure, which will not allow the transmission to function properly.
#2. Sensor Failure.
Several sensors control the engine and transmission.
When one of the sensors gives false information to the computer, such as a MAF, MAP, TPS, or speed sensor, limp mode may be activated. Failed fuel injectors, coil packs, and worn-out spark plugs can also cause limp mode.
#3. Damaged Wiring.
Damaged or broken wiring can also be a potential cause. Wires are damaged from heat, debris hitting, and even battery acid leaking onto the wiring.
A damaged wire cannot send an electrical signal properly, and as a result, the computer will think a part has failed.
#4. Failing Clutch or Transmission.
A failing or failed clutch can also cause limp mode. Improperly adjusted linkage and a bad solenoid in the transmission will initiate limp-home mode to protect against further damage to the transmission.
How to Bypass Limp Mode (3 Methods)
The first thing you need to do is find a safe place to pull over when you experience limp mode. After you have safely pulled over, there are a couple of things you can do to attempt to reset your vehicle’s computer.
#1. Check and Top Off Fluids.
The first thing to do is check your fluids. To do this, you need the vehicle on level ground. In a park with the engine running, the first fluid to check is your transmission fluid.
If it’s low, it could be the main reason for limp mode. If it doesn’t meet specs, adjust the fluid. Check the color and smell. Dirty or burnt transmission fluid can also create issues.
Once you have topped off the fluid, turn off the engine and reset your car’s ECU as explained in #2 below.
#2. Shut Off the Engine and Restart.
You can also try shutting off the engine and allowing it to sit for 5 minutes or more. During this time, you can check your engine oil level and the level of all other fluids under the hood.
Many times, this short rest will allow the computer to reset and wake your vehicle out of limp mode.
#3. Clear Check Engine Light.
Another option is to disconnect the battery cables. It is best to disconnect both cables from your battery and attach them together for 15-30 seconds. By doing this, it will drain any residual power from your computer, and your vehicle will forget all the problem codes that may be saved in memory.
Clearing these codes with a good OBD2 scanner will do the same, and is the preferred method since it is faster and more reliable.
How to Repair Limp Mode
Getting your car out of limp mode can be frustrating. The best way to repair limp mode is to use a code scanner to read the codes that the computer has stored. If your fluids are all clean and at the proper level, you can usually pinpoint the failed part this way.
An OBD/OBD2 scanner works best to read the codes, which will give you the best idea of what sensors or parts may be failing.
One thing to remember is that just because a part reads badly in the scanner, it does not necessarily mean that the part is bad. There could be a broken (or damaged) wire sending the improper signal, and that will cause the same issue.
If a part or sensor is reading badly, make sure to visually inspect the wires coming out of the part and verify conductivity with a multimeter. If electricity is getting to some point in the cord, but is not getting all the way to the sensor, that cord should be replaced.
Conclusion
Tracking down what causes limp mode can be painstakingly annoying and time-consuming, and ignoring it, or constantly resetting the computer when it happens, may lead to ever larger and more expensive repairs, or even severe safety malfunctions.
If none of the troubleshooting tips above have worked for you, it may be way past time to engage with a person in automotive repair or a reputable shop for repairs.
Every time a vehicle goes into limp mode, it should be treated like a real problem and dealt with seriously and immediately.
If you find yourself unable to remedy the problem of limp mode on the roadside, get the car towed to a garage or your home area so that it can be properly diagnosed and repaired.