What is a Limp Mode? (Causes, Symptoms and How to Fix)

While driving, sometimes your car gets slowed, making it hard to switch gears. This abnormal behavior of your car is due to the activation of the limp mode. With the activation of your car’s limp mode, the check engine light starts to illuminate, warning you about engine issues. This mode is a protective measure initiated as a result of some inappropriate sensor readings by the car’s computer to prevent the engine from being damaged. This article mainly explains the causes and symptoms of the limp mode.

What is a Limp Mode?

Limp mode is a safety mode of the car that turns on automatically and protects the engine from damage. It is initiated upon receiving some inappropriate or faulty readings from the transmission control system or engine. It prevents the transmission system and engine from severe damage.

Another name for limp mode is “limp home mode,” and in diesel vehicles, it is also known as “engine derate.

Limp Mode

Limp home mode limits the engine speed, reduces the power, and makes it possible for you to take your car successfully to the service center without damaging the engine.

For instance, the Engine Control Unit (ECU) shows your car’s turbo boost pressure as 1.8 bars which should be 1.3 bars. This excessive Turbo boost pressure can damage your car’s engine. Therefore, the ECU will automatically activate the limp home mode.

Maximum vehicle owners do not pay much attention to the engine lights and do not bother checking them properly. Therefore, in such conditions, the ECU turns on the limp mode, completely turns off the turbo boost, and automatically sets up the reverse speed as 3000rpm to avoid damage.

Symptoms of Limp Mode

As the car computer activates the limp mode, it produces one of the below-given symptoms:

  1. Trapped Gear
  2. Poor Performance
  3. Limited RPM
  4. Lower Engine Power
  5. Check Engine Lights 

1) Lower Engine Power

One of the significant symptoms of a car being in limp mode is the reduction in its overall engine power. A sudden decrease in engine power or RPM refers to your car as in limp mode. This happens due to the immediate halt of the turbo boost pressure of your car.

Reduced engine power

Some of the cars may not have turbo boost, but in limp mode, the excessive power of their engine gets limited or reduced. 

2) Check Engine Light

Whenever a car goes on limp mode, check engine lights display the warning glow on the dashboard. However, there are multiple causes of check engine light illumination. To find out the exact issue, you can check the codes (P0017, P0013, P0031, etc.)  through the OBD2 scanner.

check engine light

Read More: Causes of Check Engine Light Flashing

3) Limited RPM

A reduction in the vehicle speed or rpm is one of the most common signs of the limp mode. The speed of the car can be limited to less than 3000, and the driving speed can also be limited from 35 to 45 MPH. Therefore, limited RPM in limp home mode makes it difficult for you to run your car on highways where you can’t shift above 3rd gear.  

Limited RPM

4) Poor Performance

Within limp mode, the acceleration of the car gets lower, and it feels like the engine is falling. As a result of such poor performance, it may feel hard to shift different gears due to the abrupt downshift in the car’s transmission system. 

Poor Performance

5) Trapped Gear

When a car goes into Limp Mode, the driver finds it difficult to switch between the gears due to the reduction in engine power and limited RPM. 

Trapped Gears due to limp mode

So, whenever you feel like the transmission system of your car is locked, it is a strong sign that your car is in limp mode. The strongest sign is that your transmission will not shift up more than the 3rd gear.

Causes of Limp Mode

The following are the most common causes of your car’s limp mode:

  1. Turbo Boost Pressure
  2. Defective Engine Sensors
  3. Low Fluid Level
  4. Faulty Wiring
  5. Bad Transmission or Clutch

1) Turbo Boost Pressure

Activation of the limp mode in the advanced car is mostly due to the excessive turbo boost pressure.

Turbo Boost Pressure

Whenever the turbo boost pressure of a car becomes over normal pressure, the car control system automatically activates the limp home mode to prevent the car engine from being damaged and some serious noticeable issues.

Sometimes the low turbo pressure may also lead the car computer to activate the limp home mode. That is because your car is unable to maintain a reasonable pressure for perfect functionalities; due to that, it goes into limp mode.

Issues with a wastegate, boost control value, boost pipe leak, turbocharger, and boost pressure sensors can be the reason for the turbo boost pressure problems.

2) Defective Engine Sensors

Sometimes, wrong readings of the engine sensors (like oil sensor and coolant sensors reading) force the engine control unit to activate the limp mode. Various sensors are connected to the car’s computer. These sensors transfer readings of different engine parts to the computer.

engine sensor

It is difficult to detect exactly which sensor is causing limp mode. Commonly O2 sensors, MAP sensors, boost pressure sensors, engine temperature sensors, and MAF sensors cause limp mode.

3) Low Fluid Level

Low transmission fluid or engine oil level in your car can also be the reason for limp mode. So, the transmission fluid level depends on the pressure created in the transmission system of the car. So, a low transmission fluid level will create low pressure and result in the improper working of the transmission system and limp mode.

fluid level mark in the power steering reservoir

The engine oil uses to properly lubricate the parts of the car engine. It also helps to prevent the engine from overheating issues. When your vehicle has low oil, it leads to engine overheating and activates the lamp mode.

Read More: How to change car engine oil?

4) Faulty Wiring

Electronic components are the major constituent of advanced cars and need wires to connect and work properly. With time, most car wires can get damaged due to heat, acid, hitting, or cutting. These damaged wires may be one of the causes of the activation of limp mode in a car.

Faulty Wiring, Limp mode

The faulty or damaged wire doesn’t properly transfer the electrical signals to the engine control unit (ECU), and the computer marks the part or sensor as a failed part.

5) Bad Transmission or Clutch

A bad transmission system is one of the major causes of limp mode.

Some minor issues in the transmission system like bad linkage and bad solenoids can also activate the limp mode of the vehicle to prevent the car from future damage.  

How to Fix Limp Mode?

A proper diagnosis is a pivotal step toward a perfect fix of limp mode. Limp mode diagnostic is like properly analyzing what is faulty and replacing it accordingly. Without a proper diagnosis, you will just throw money to replace the random parts of your car and feel lucky if you get rid of limp mode.

Follow the below-given steps to fix the limp mode of your car:

1) Check All fluids

The first step of the limp mode fix is to check the level of all the fluids in your car one by one. Engine oil, brake fluid oil, transmission fluid, power steering, and coolant should be checked sequentially. 

Ensure all the fluids are up to their optimal levels, healthy and normal. You can smell them as well. Use the vehicle manual to see after how long these fluids need to be replaced or refilled. Replace or refill them if needed.

2) Check Air Filter

The purpose of the air filter is to provide dirt-free clean air to the engine. In most cases, air filters are dirty or get damaged due to some reasons and provide dusty air to the engine. That dust can clog the filter and cause issues with the engine air intake.

Usually, car manuals have a proper schedule for changing the air filters. Keep an eye on the dates and change the filters from time to time to avoid further damage.

Fortunately, the replacement of the air filters is a cheap and easy process. It doesn’t need much time or money to be cleaned. 

3) Clean MAF Sensor

The purpose of the MAF sensor is to control the air-fuel mixture in your car. In the case of open-air filters, MAF sensors get dust quickly. Due to the dirt and dust layer, it doesn’t send perfect readings to the ECU, resulting in limp mode.

Cleaning the MAF sensor head is the cheapest fix to limp mode. Follow the below-given steps to clean the MAF sensor:

  1. Remove the dirt and clean the sensor with the help of an electronic cleaner.
  2. Because sensors are highly sensitive, do not touch the sensor with the help of your hand or towel.
  3. Always use electronic cleaners to clean the MAF sensor.
4) Check Trouble Codes

If you have worked on all the fixes discussed above and have no luck, then you need to perform the full diagnostic test and work on the error codes.

For a proper diagnostic of your car, you can visit your mechanic or do it through an OBD2 scanner at home. One-time spending on a scanner allows you to use the scanner in the long run and saves time.

How to Diagnose Limp Mode?

To find the cause of the car’s limp mode, the mechanic performs a few steps and finds the issue. Few advanced tools are needed for a complete perfect diagnostic of your car. You can follow these steps to diagnose the exact causes of limp mode:

  1. Connect the OBD2 scanner and check for trouble codes. Whenever the Limp mode activates, the trouble codes get stored in the ECU of your car. But if you are having trouble finding codes, try another diagnostic scanner.
  2. Search for the Trouble code about what exactly it shows or it depicts. For this information hunt, you can use any website or your car’s manual.
  3. Now, check whether the boost pressure sensor is providing realistic readings when idling or not. Replace the sensor if there is any issue. 
  4. Test the waste gauge with the help of a vacuum or pressure gauge. Please make sure it should move freely while testing.
  5. Test the boost control sensor through a diagnostic tool while pressurizing the wastegate. Replace if faulty.
  6. Use EVAP smoke machine to check intake leaks. Repair or replace if you observe any damages or faults.
  7. Check the values of the throttle position sensor, air temperature sensor, MAF sensor values, O2 sensors, and engine coolant temperature sensor. Likewise, replace them if they need replacement.
  8. All done! Your diagnostic is complete.

FAQ Section

What does a car do in limp mode?

Limp mode, also known as “Limp home Mode, ” is a protective mode activated when a car detects any fault in its transmission control unit. With the activation of Limp mode, the air conditioner gets off, and turbo pressure gets reduced with limiting RPM. It’s like a power-saving car mode that saves the engine from further damage.

Can I bypass limp mode?

Yes. Bypassing limp mode is possible. You can restart the vehicle and remove one of the battering terminals to reset the system. You can also check the fluid levels for a quick fix.

How much does it cost to fix limp mode?

Cost depends on the cause. Usually, the limp mode is fixed by fixing the faulty parts of your car or refilling the fluids at their optimal level. Hence, the cost of the fix is not fixed; it depends on what part you are repairing. But simply ignoring the limp mode can result in huge costs and damage.

What are the signs of Limp Mode?

  1. Trapped Gear
  2. Check Engine Light 
  3. Poor Performance
  4. Lower Engine Power
  5. A reduction in the speed

What are the causes of car limp mode?

The following are the major causes of the car limp mode:

  1. Bad Transmission or Clutch
  2. Turbo Boost Pressure
  3. Faulty Wiring
  4. Defective Engine Sensors
  5. Low Fluid Level
Read More
  1. Symptoms of a bad MAP sensor
  2. Symptoms and Causes of a bad IAP Sensor
  3. Different types of Engines
  4. Signs and Causes of low Transmission Fluid
  5. Causes of Soft Brake Pedal

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