What is a Limp Mode? Causes, Symptoms, & How to Bypass It

While driving, there may be times when your car experiences reduced performance, making gear shifting difficult. This unusual performance of your vehicle usually occurs because of the activation of the limp mode, a self-protective feature featured in most automobiles. The car initiates this function when it identifies unusual sensor readings or improper functioning of engine components. This article explains the limp mode causes, symptoms, and how to fix it.   

What is a Limp Mode?

The limp mode, also known as the safety mode, is a feature in the latest vehicle models that assists in preventing the transmission and engine from damage when an issue is identified.

limp mode

As the engine control module (ECM) of your vehicle monitors an issue with your vehicle’s transmission or engine, it may trigger the limp mode, which restricts the RPM and power of your engine. The main purpose of the limp mode activation is to prevent further damage to the car and to ensure that you can still safely drive it to a service station for repairs.

Moreover, when the ECM of your vehicle triggers the limp mode, it may also modify ignition timing (postpone the ignition moment for each cylinder) or alter valve timing (change when the intake valve and exhaust valve open).

For instance, if your PCM monitors a turbo boost pressure of 1.0 bar while the maximum allowable boost pressure is 0.5 bar, it may potentially harm the engine; as s a result, the PCM triggers the limp mode.

Limp Mode Symptoms

When your car computer activates the limp mode, you may notice one or more of the below-given symptoms:

  • Check Engine Light Illumination
  • Unresponsive Accelerator Pedal
  • Overheating
  • Lower Engine Power
  • Can’t Shift Beyond 3rd Gear
  • Poor Engine Performance

1) Check Engine Light Illumination

The check engine light is one of the first symptoms when your vehicle enters limp mode. This light may appear alongside a transmission warning light or a similar warning signal.

Check engine light

Your vehicle’s check engine light can be triggered for numerous reasons, so its presence alone does not necessarily indicate that your car is in limp mode.

To determine the cause of the check engine light, it’s essential to use an OBD-II scanner to read the diagnostic trouble codes.  

2) Unresponsive Accelerator Pedal

Accelerator Pedal, symptoms of limp mode

You may be accustomed to a responsive accelerator pedal, but in limp mode, the responsiveness of the accelerator pedal usually diminishes. This is a most common issue in the latest vehicles. If you find yourself needing to press harder before the vehicle’s engine revolution, the vehicle could be in limp mode.

This sudden change is another way to confirm that it’s not related to other issues. In maximum conditions, the responsiveness of the accelerator pedal slowly reduces due to wear and tear or damaged accelerator components.

When the vehicle enters limp mode, the transition is smooth and serves as a safety measure to protect you and your vehicle from driving under hazardous conditions.

3) Overheating

car Overheating

In extreme cases, the limp mode may also lead to engine overheating. This warning sign indicates that you should stop the vehicle and let your vehicle cool down before proceeding. Allowing the engine and transmission to cool down for some time minimizes potential damage they may incur.

4) Lower Engine Power

A clear sign of a car operating in limp mode is the poor engine power. An unexpected drop in engine power or RPM suggests that the vehicle is in limp mode, which occurs due to an abrupt stop in the turbo boost pressure.

Poor Engine Power, signs of limp mode

For vehicle models without turbo boost, the limp mode will still limit or reduce the engine’s excessive power output.

5) Can’t Shift Beyond 3rd Gear

If your vehicle does not shift beyond third gear, this is a clear indication that the vehicle is in limp mode.

Gear Shifting issues

This sign is more common in vehicles with automatic transmissions. In such situations, your vehicle’s ECM will prevent the gearbox from shifting past third gear in order to maintain a low speed, which may be challenging to detect when driving less than 40 mph in specific situations.

6) Poor Performance

Loss in Performance

When your car is in limp mode, the car’s acceleration diminishes, and it looks like the engine is sluggish. Due to this reduced performance, shifting gears may become difficult as a result of the sudden downshift in the transmission system.

Limp Mode Causes

The main computer of your vehicle triggers the limp mode due to one or more of the below-given causes:

  • Turbo Boost Pressure
  • Transmission Failure
  • Damaged Wirings
  • Low Transmission Fluid Level
  • Misfiring
  • Overheating
  • Overboost
  • Faulty Sensors
  • Vacuum Leaks
  • Missing Emission Components
  • Faulty Spark Plug

1) Turbo Boost Pressure

One of the most common causes for a car to activate limp mode is an issue with the turbocharger pressure. This usually occurs when the boost pressure becomes too high. In such a situation, your vehicle engages limp mode to avert significant engine damage.

However, your vehicle computer may also activate this mode if the turbo pressure becomes very low or if turbocharge fails to build up the required boost pressure.

Common reasons for boost pressure issues include the boost pipe leakage, boost pressure sensor, wastegate, boost control valve, or a malfunctioning turbocharger.

2) Transmission Failure

If you have an automatic transmission vehicle, the transmission control module (TCM) of the vehicle can trigger the limp mode if something is wrong with the transmission.

This mode may also be triggered due to a damaged shift solenoid, low transmission fluid, a faulty valve, or a bad sensor.

Transmission Issues

Limp mode is also activated when the TCM detects a broken, damaged, or defective clutch in your vehicle.

Read More: Transmission Slipping Causes

3) Damaged Wirings

Your engine contains a series of different electrical wires that are used to provide power to all electrical components of your car. Consequently, the electrical system is one of the most vital parts of your vehicle’s internal system, and it is also among the most sensitive.

Damaged Wiring

Factors such as dirt, moisture, extreme cold, and engine heat can cause the electrical wiring to be damaged over time. These damaged wires may interfere with you’re the other systems of your vehicle, initiating limp mode.

For example, a damaged wire to the boost pressure sensor could prevent the PCM from regulating it properly. Moreover, a faulty boost pressure signal may prompt the PCM to engage in limp mode as a precautionary measure.  

4) Low Transmission Fluid Level

Transmission fluid is compulsory for the efficient performance of the transmission system. It serves as a lubricant to minimize unnecessary friction between moving parts of the transmission system.

Transmission Fluid Leak

This fluid also protects your transmission from damage and stress. Ensuring a sufficient supply of transmission fluid is crucial for keeping your transmission in optimal working condition.

If there is an insufficient amount of fluid, a drop in pressure may occur in your transmission system, causing it to malfunction and activate the limp mode.

Read More: Causes of Transmission Light Illumination

5) Misfiring

Knocking noises coming from the engine compartment typically signify different potential problems. The knocking sound is usually produced due to a poor air-fuel mixture within your engine.

Engine Misfiring, causes of limp mode

If your vehicle persistently knocks or misfires, not only will you see a check engine light, but you may also experience limp mode as an added consequence.

Read More: Engine Misfires Symptoms and Causes

6) Overheating

When the cooling system of your car doesn’t work efficiently, it doesn’t efficiently manage the heat produced by the engine, leading to overheating. The engine overheating may damage the parts of your engine and hinder its performance.

Symptoms of Engine Overheating

Regular overheating may cause your car to enter limp mode. In this situation, the PCM will limit power to specific parts of the vehicle’s engine, allowing cool air to help lower the temperature of your overheated engine.

Read More: Causes of Engine Overheating

7) Overboost

This issue usually occurs when the turbocharger takes in more air than the engine control module (ECM) allows. While this can improve engine performance, but it poses the possibility of engine damage.

If the PCM of your car detects an over-boost situation due to a component malfunction, it will activate the limp mode, preventing severe engine failure.

8) Faulty Sensors

Your vehicle is equipped with numerous sensors necessary for its proper functioning. For example, the manifold absolute pressure (MAP) sensor provides real-time manifold pressure information to the ECM, the throttle position sensor (TPS) measures how hard you’re pressing on the gas, and the speed sensor measures your car’s speed. These sensors work together with many others to keep the vehicle running smoothly.

If the ECM doesn’t receive precise readings from any of the sensors, it will activate the limp mode. It’s essential to regularly check these sensors to ensure their efficient performance.

9) Vacuum Leaks

A vacuum leak occurs when your engine takes in more air than the PCM allows, typically caused by faulty air intakes.

Vacuum Leak

When the ECM of your vehicle detects that the air/fuel ratio is not according to the requirements, it triggers limp mode along with the check engine light.

Read More: Vacuum Leak Symptoms and Causes

10) Missing Emission Components

The muffler deletion also removes a sensor associated with it. When the ECM detects that a particular sensor is missing, it triggers the limp mode. Moreover, car manufacturers dedicate significant time and resources to engineering the entire vehicle, including its emission-control equipment.

11) Faulty Spark Plug

Spark Plug

A faulty spark plug is one of the most common reasons for the limp mode. When your vehicle enters limp mode, the check engine light may remain on or flash.

In case of a bad spark plug, your engine will perform poorly, and it might shake in case of a misfire. In some cases, a bad spark plug or a damaged ignition coil can cause a cylinder misfire, where one or more of your cylinders stop functioning.

Driving a vehicle with a misfiring cylinder can damage the catalytic converter and increase the likelihood of the engine overheating.

How To Reset Limp Mode

It’s generally not recommended to bypass limp mode; however, if you have a valid reason and understand the potential consequences, you may choose to do so.

Keep in mind that if your car enters limp mode, there is an issue with the vehicle, and continuing to drive it using standard transmission or engine settings could cause additional damage to the powertrain.

To fix or bypass the limp mode, you can use one or more of the below-given methods:

  • Switch off the engine and restart it
  • Disconnect and reconnect the battery
  • Check all fluids
  • Inspect air filter
  • Clean MAF sensor
  • Clean MAP sensor
  • Replace the faulty spark plug
  • Check trouble codes
  • Contact a professional
1) Switch off the Engine and Restart It

Safely park your vehicle and switch off the engine. Wait for around 6 to 10 minutes before restarting your engine to see if high gear can be engaged.

2) Disconnect and Reconnect the Battery

If the issue persists, remove the negative terminal of your car’s battery for approximately 25 minutes. Reconnect the terminal and test gear shifting to check if the problem is resolved.

3) Check All Fluids

The initial step in resetting limp mode is to individually inspect the levels of all fluids in your vehicle. These fluids include coolant, power steering fluid, brake fluid, transmission fluid, and engine oil.

You need to make sure that all fluids are according to the manufacturer’s recommendation and in good condition. You may also check their smell. Consult your vehicle manual to determine when these fluids need to be refilled or replaced, and do so if necessary.

4) Inspect Air Filter

Air Filter, how to reset limp mode

The air filter’s function is to supply clean, contamination-free air to the combustion chamber. Sometimes, your air filter may become damaged or dirty, providing contaminated air to the combustion chamber. This contamination may block the filter and lead to problems with the engine’s air intake.

Typically, your vehicle manual includes a schedule for replacing the air filter. Monitor the dates and replace the filters periodically to prevent further damage. Replacing an air filter is an affordable and straightforward process that doesn’t require much time or money.

5) Clean MAF Sensor

MAF Sensor

The mass airflow (MAF) sensor regulates the air/fuel mixture in the vehicle engine and may also become dirty, particularly with an open-air filter. The contaminants on your MAF sensor may cause it to send the wrong information to the PCM, potentially triggering limp mode.

However, MAF sensor cleaning is relatively inexpensive and easy. Remove the sensor and carefully clean it with an electronic cleaner. Keep in mind that the sensor is delicate, so avoid touching it with a towel or your hands.

6) Clean MAP Sensor

A faulty or clogged MAP sensor may also trigger the limp mode in some vehicle models. The MAP sensor is used to measure the air pressure in the intake manifold and sends this data to the PCM. The PCM utilizes this information to measure the precise air-fuel mixture for the engine.

Read More: Bad MAP Sensor Symptoms and Causes

7) Replace the faulty Spark Plug

As mentioned above, your vehicle’s computer may trigger the limp mode due to a faulty spark plug. Inspect your spark plug and replace it if needed.

8) Check Trouble Codes

If you’ve tried all the previously mentioned fixes without success, it’s time to conduct a full diagnostic test and address the error codes.

Utilize an OBD-II scan tool to identify any error codes in your vehicle’s system. These codes may help diagnose the issue. Clearing codes might offer a temp solution, but a significant problem could trigger the check engine light again.

9) Contact a Professional

If you lack the expertise to tackle complex issues like limp mode, it’s advisable to seek help from a professional mechanic. While this may be costly, but it can save you time and frustration. In fact, having a mechanic diagnose the car could potentially save you money by avoiding the replacement of incorrect parts.

How to Diagnose Limp Mode?

Follow the below-given steps to diagnose the limp mode:

  • Use your OBD-II scanner to scan the trouble codes. When the limp mode is activated, the trouble codes are stored in your vehicle’s PCM. If you have difficulty reading the codes, try using a different diagnostic scanner.
  • Research the trouble codes to understand what they indicate. You can refer to websites or the vehicle manual for this information.
  • Verify if the boost pressure sensor provides accurate readings while the car is idling. If there are any issues, replace the sensor.
  • Test your vehicle’s wastegate using a pressure or vacuum gauge. Ensure that it moves freely during the test.
  • Examine the boost control sensor using a diagnostic tool while pressurizing the wastegate. If it’s bad, replace it.
  • Employ an EVAP smoke machine to find an intake leak. Repair or replace any damaged or faulty components you find.
  • Review the values of the O2 sensors, throttle position sensor, MAF sensor, air temperature sensor, and engine coolant temperature sensor. Replace any that require replacement.

FAQ Section

Can I bypass limp mode?

Yes, you can try bypassing limp mode by restarting your car after waiting briefly or by disconnecting the negative terminal of the battery to reset the electronic systems. Additionally, you should also inspect the fluid level to determine if that is the cause of the issue or reset the error electronically to check if it was just a temporary problem.

Can I drive my car in limp mode?

While it is possible to drive the vehicle with limp mode, but it is not advised and should only be done when driving to a professional. Running a vehicle in limp mode may assist you in reaching a workshop without causing additional damage to the engine. But the ideal approach – to be absolutely certain – is to have your vehicle towed to a repair shop instead of driving it.

How long can I drive a vehicle with limp mode?

There isn’t a specific number of miles or kilometers that you may drive in limp mode. The main aim of the limp mode and check engine light is to alert the driver to an issue with the vehicle engine.

Can a bad battery activate limp mode?

Yes, a faulty battery may trigger the limp mode, but it is not a usual cause. You’re more likely to experience other problems with the vehicle if your battery is bad. But low voltage can lead to various issues with the vehicle’s electronic computers, including limp mode.

What sensors can cause limp mode?

  • Throttle position sensor (TPS)
  • Transmission fluid temperature sensor
  • MAF sensor
  • O2 sensor
  • MAP sensor
  • Crankshaft position sensor
  • Speed sensor
  • Engine coolant temperature sensor
  • Camshaft position sensor
  • Knock sensor

How fast can I drive in limp mode?

This depends on what parameters the manufacturer has set; in most cases, you will be limited to no more than 30mph to 50mph and will not be able to rev the car above 3,000 rpm or change into higher gears if it is automatic.

Do all cars have limp mode?

All cars don’t have limp mode, but the latest vehicle models with electronic control units (ECUs) and advanced engine management systems have it. Limp mode is mainly installed in vehicles designed in the late 1990s and newer. The traditional vehicle models with basic electronic systems or purely mechanical systems usually don’t contain a limp mode feature.

Is driving in limp mode damage the car?

Yes, driving your car in limp mode may damage your car. Your vehicle’s computer activates the limp mode to prevent the vehicle from further damage.

Leave a Comment