Have you ever experienced your car suddenly losing power, and you could not accelerate beyond a certain speed? This may be due to your car’s limp mode being activated.
Take this warning seriously because your vehicle likely has a major problem. Keep reading to learn what causes limp mode, symptoms you can expect to appear, and how to bypass limp mode if the situation calls for it.
What is Limp Mode?
Limp mode is a self-preservation feature programmed into most vehicles. Your car will activate this feature when it detects abnormal readings from sensors, or improper mechanical part operations.
Limp mode is also known as “limp home mode”, and is designed to protect your engine and transmission from catastrophic failure. Most diesel vehicles have a similar mode referred to as “engine derate“.
Performance of your vehicle will be greatly reduced by the computer to prevent major damage but allow you “limp” your car home, a nearby auto repair shop, or simply off to the shoulder where a tow truck can be called.
When activated, your car is telling you there is a serious problem and this issue should be addressed immediately. It is imperative you get to a safe location as soon as possible and attempt to identify why limp mode has occurred.
3 Symptoms of Limp Mode
#1 – Limited Speed and RPM
When active, your car may exhibit a variety of symptoms. Limp mode limits the amount of power to your engine and transmission.
RPMs may be limited (usually to less than 3,000), and your driving speed will often be limited to about 35 to 45 MPH, making it impossible to drive at highway speeds and you may find yourself unable to shift above 3rd gear.
#2 – Poor Performance
Acceleration will be sluggish and you may feel your engine shuddering or misfiring.
You may find that your transmission automatically downshifts and you’re unable to shift above 3rd gear or maybe even not be able to shift gears at all.
#3 – Check Engine Light
The check engine light will illuminate or flash, and depending on the failure, you may notice your vehicle overheating.
If overheating occurs, you must immediately pull over off the road and give your car time to cool down to prevent further damage to the engine and transmission before attempting to drive any further.
See Also: DPF Warning Light (Diesel Engines)
4 Common Causes of Limp Mode
While limp mode can be caused by many different problems, there are a few common causes that can be easily identified.
#1 – Low Fluid Level
Low fluids, especially transmission fluid and oil, can cause a vehicle to enter limp mode.
This is especially true of the transmission fluid, since low fluid can cause low pressure, which will not allow the transmission to operate properly.
#2 – Sensor Malfunction
There are quite a few sensors which control the engine and transmission. If one of the sensors, such as the MAF, MAP, TPS or speed sensors are sending improper signals to the computer, limp mode can activate.
Failed fuel injectors, coil packs and worn out spark plugs can also cause it.
#3 – Damaged Wiring
Damaged or broken wiring can also be a potential cause. Wires can be damaged by heat, debris hitting them, or even battery acid leaking onto them.
A damaged wire cannot send a proper electrical signal, making the computer believe a part has failed.
#4 – Failing Clutch or Transmission
A failing or failed clutch can also cause a vehicle to enter limp mode.
Improperly adjusted linkage, and bad solenoids in the transmission will activate limp home mode in order to prevent further damage to the transmission.
How to Bypass Limp Mode (3 Methods)
If limp mode occurs, the first thing to do is find a safe spot to pull over at. Once pulled over, there are a few things you can do to try and reset your vehicle’s computer.
#1 – Check and Top Off Fluids
The first thing is to check your fluids. To do this you will need to be on level ground. With the vehicle in park, and the engine running, first check your transmission fluid.
If it is low, this is most likely your culprit. Adjust the fluid to with proper specifications, and take note of the color and smell. Dirty or burnt transmission fluid can cause issues as well.
Once fluid is topped off, shut off the engine and reset the car’s ECU as shown in #2 below.
#2 – Shut Off Engine and Restart
The next fix you can try is to shut off the engine and let it rest for at least 5 minutes. During this time you can check the engine oil level, as well as the level of all the other fluids under the hood. Sometimes, this brief rest will allow the computer to reset itself and bring it out of limp mode.
#3 – Clear Check Engine Light
A third option is to disconnect the battery cables. It is best to pull both cables off the battery, and hold them together for 15 to 30 seconds. This will drain any residual power from the computer and cause it to forget any codes that may be stored.
Clearing the codes with an OBD2 scanner will achieve the same results and is faster and safer.
How to Fix Limp Mode
Due to the complexity of limp mode, the best way to fix it, is by using a scanner to read the codes stored in the car’s computer. If all fluids check out clean and are at the proper level, this is the best way to identify failed parts.
An OBD/OBD2 scanner will read the codes, which can then point you towards which sensors or parts need replacing.
However, it is important to keep in mind, that just because a part is reading bad on the computer, it doesn’t necessarily mean that part is bad. A broken or damaged wire can cause the part to not send the proper signal.
If a sensor or part is reading bad, be sure to visually inspect the wires coming out of that part, and verify conductivity with a multimeter. If electricity is reaching a certain spot in the wire, but not all the way to the sensor, that wire should be replaced.
Tracking down the cause of limp mode can be vexing and time consuming, and ignoring it or constantly resetting the computer to avoid it can lead to even more costly repairs, or severe safety malfunctions. If none of the above fixes have helped, it is ideal to seek out repairs at a reputable automotive repair shop.
Any time a vehicle enters limp mode, it should be treated as a serious problem and be immediately addressed. If you find yourself unable to fix the problem on the road, have your car towed to a garage or your house where issues can be safely and accurately identified and repaired.
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