Reduced Engine Power Warning: What Does It Mean?

From commuting to work to driving the kids to school, a car is part of your daily routine in numerous ways. And, it is understandable that when you experience reduced engine power, a vehicle’s sluggish response to your gas pedal is a huge concern.

Older vehicles faced challenges such as needing to replace spark plugs or wires, replacing rotors and distributor caps, and adjusting carburetors. These days, though, you will face a broad range of more modern problems that can be behind your vehicle’s issues with acceleration.

This article seeks to explain all the possibilities for reduced engine power. Read on to learn everything there is to know about why your vehicle accelerates sluggishly.

What Does ‘Engine Power Is Reduced’ Mean?

Having the alert ‘engine power reduced’ in your system has a critical meaning. Simply put, this is a signal that something is not right. In addition to that, failure of your vehicle’s computer system will result in activating “limp mode” to avoid further system damage.

In this condition, your vehicle is unable to accelerate any further. This protective measure is in place to restrict the engine’s power for your safety. Many reasons might cause this, including major component failures or simple sensor malfunctions.

Learning how to interpret this warning can keep you safe on the roads while preventing expensive repairs.

Trouble Codes that Are Related to Reduced Engine Power

Depending on the vehicle you own and the issues detected by your ECU, different trouble codes will be logged into the ECM memory. These trouble codes include:

• P0120-P0124: This indicates the malfunction of either the pedal position or throttle position device and their circuitry.
• P1125: This indicates a bad system or component fault, but it depends on the year, make, and model of the vehicle.
• P1518: Points to a bad system or defective system element fault, but the vehicle’s make and model will certainly determine this.
• P2111: This code indicates that the throttle actuator control system is stuck in the fully open position.
• P2135: This indicates the problem with the APP, TP sensor, or switch with one of the A/B voltages opening or closing.

For effective and thorough diagnosis and repairs, the vehicle has to be brought to a local service shop to be checked by a professional mechanic.

What is Fail-Safe Mode?

The message of “engine power reduced” indicates that your vehicle has developed a problem and has shifted into a fail-safe mode. Every contemporary car features a safety net that has been strategically implemented to protect drivers.

In an attempt to safeguard the individual utilizing the car or to restrain the damage that may occur to the vehicle itself, the car’s ECU might switch to fail-safe mode. It is important to note that there are multiple ways in which the onboard electronics of a car can put it into a failsafe mode, all of which differ in the capacity they allow to perform.

For instance, in the case that the electronic throttle actuator is malfunctioning, the electronic throttle control unit can adjust the maximum throttle opening to a lower level. Alternatively, in a scenario where the issue lies with the transmission system, the control unit may restrict transmission function to a specific set of gears.

Some makes and models of vehicles are designed to show specific notifications on the control panel alerting the user that the automobile is operating in a fail-safe mode. For other vehicles, an illumination of the check engine may indicate the same functionality.

Common Signs of Reduced Engine Power

On its own, the warning light indicates a greater issue. Before it even turns on, there are a few symptoms indicating the issue of the engine’s power running low. These signs may include:

• Diminished Acceleration: Your vehicle finds it difficult to accelerate, particularly when driving on expressways.
• Irregular Performance: The vehicle might behave differently with unstable idling, difficulty in maintaining steady speeds, or higher than usual noise levels.
• Decreased Fuel Efficiency: The vehicle’s performance has diminished and requires more frequent refueling.
• Check Engine Light: The check engine light can come on either before or simultaneously with the reduced engine power indication. This is a critical condition that should not be neglected.

These are only a few of the most basic signs. They are not specific to any model of vehicle, which means no matter the make of the vehicle you drive, it is essential to monitor your vehicle’s performance and any changes that may happen.

What Causes the “Reduced Engine Power” Message?

The problem that triggers the reduced engine alert is similar to the alternative action of turning on your controller engine light. An engine alert in the mind of a driver can have multiple possibilities.

The make and model of your GM vehicle play a huge role in determining your vehicle’s service message. Furthermore, the year of the vehicle the user owns will also play a part in tackling the “check service” alert light issue.

Although several reasons could cause your engine to reduce alert, some have been proven to be more frequently mentioned than others. One of the main reason,s which are self explanatory, is likely to be:

Electronic Throttle Actuator (Throttle Body) Problems 

One of the potential and simplest responses is an issue within the electronic throttle actuator control system (TAC).

This form of technology first came on the C5 Corvette in 1997. More and more GM vehicles have been turning to TAC and forsaking classical throttles and linkages.

TAC systems come with their pros. For one, the PCM checks two APP sensors, and based on that, the APP estimates the acceleration as defined by the throttle response. Additionally, two throttle position TP gauges help in monitoring the predicted movement.

Having gathered the required data from the sensors, the module uses an actuator motor located at the throttle body to modulate the throttle. This regulation of the throttle informs the air flow to the engine.

Failure to clean the throttle body can trigger the Reducing Engine Power mode.

Bad Pedal Position Sensor

Any issue in the TAC system can unceremoniously trigger the Reducing Engine Power indication on the dashboard. The problem may lie in none or one of the APP sensors, which are found on the accelerator pedal and are usually paired.

Faulty Throttle Position Sensor

The TAC system also relies on information from two other inputs, the TP sensors. When one or both of the sensors go bad, the vehicle will enter into reduced engine power state.

Such problems normally arise from excessive wear due to dirt or failure of the throttle body, which controls airflow into the engine. A faulty or bad sensor can send out rogue information, resulting in erratic control engine performance and resulting in less power.

Circuit Issues

Problems with circuitry, like cut wires with unsatisfactory connections, result in the TAC system not functioning as intended. This will cause a combination of issues, such as the car entering the Reduced Engine Power mode.

PCM or Data Network Problems

As with many modern vehicles, there are dozens of modules, or computers, for each vehicle that communicate over a data network.

PCM issues or mid-network connection failure cause the vehicle to enter Reduced Engine Power mode.

Idle Relearn Procedure Needed

For several GM vehicles, whenever the throttle body is cleaned or replaced, an idle relearn procedure is mandatory. If this is not done, the vehicle may enter the Reduced Engine Power Mode.

Cooling System Issues

Some GM vehicles will go into Reduced Engine Power Mode when the engine starts to overheat due to a coolant system problem. This mode is activated by the PCM to prevent further possible engine damage.

All fluids should be maintained at the recommended levels to prevent this. Low engine oil and coolant levels may trigger this alert.

Engine Performance Problems

It is possible that the Reduced Engine Power alert light may go on as a way for the system to warn drivers about lack of power due to a hidden problem.

As an example, one might have a wrong high-pressure fuel pump which may cause the engine power to reduce triggering the warning light.

Diesel Engine Performance Problems

The illumination of the Reduced Engine Power warning for a Duramax diesel engine can occur due to multiple reasons.

There are numerous different technical service bulletins (TSBs) from different providers dealing with various issues on the same Duramax engine, all of which mention the vehicle going into Engine Power Reduced mode. Every single document provides a different explanation for why, including a broken MAP sensor clip or an air intake leak.

Loose Connection

For performance parts for the engine, all computers are connected with wires. In case any problem occurs in this area, the computer will alert the user through a light, commonly known as the dashboard light.

The scope of problems that can cause a RED engine light vary from as little as a loose screw to broken connection wires. Many can be solved with minimal effort, while complicated ones may require a network-wide evaluation.

Faulty Alternator

An alternator that is going bad cannot deliver enough power to the engine, which causes it to shut down partially. This may trigger a Reduced Engine Power warning.

Low Voltage Batteries

A disconnected battery does not deliver the necessary level of energy needed when almost drained and done discharging, which triggers the engine to turn off with power. This then pulls the Reduced Engine Power warning.

The engine keeps running until the battery empties; past this point, the power availability stops.

What Causes Fail-Safe Mode?

Similar to when there is a warning for “Reduced Engine Power”, your vehicle may enter a fail-safe mode for numerous reasons. Below is a list of some possible causes:

• Automatic Transmission Troubles: Any problems with your vehicle’s transmission or the electric controls may force its transmission into fail-safe mode. This is what is often referred to as „Limp Mode”. In this case, the transmission line pressure is likely to rise, and the unit defaults to a set gear.
• A Faulty “Drive-By-Wire” System: Modern-day vehicles come with an automated system called drive-by-wire that does away with the mechanical sides of steering with complex electrical systems. Most of the time, when something goes wrong with one of these systems, the ECU has no choice but to limit the car’s performance to protect the vehicle and everyone in and around it.
• Charging System Problems: Older models have numerous electronics that rely on the power of the battery. In some cases, a weak battery can decrease their performance, resulting in the vehicle to enter a fail-safe mode. If your alternator is undercharging or overcharging, this could possibly trigger the fail-safe mode as well.
• Faulty or Damaged Wiring: Faulty or loose wiring can inhibit the proper functioning of a vehicle’s onboard electronics. This, in turn, can cause numerous issues, including the inability for the vehicle to operate; it instead goes into fail-safe mode.
• Engine Performance Troubles: Alongside other performance-related issues such as overheating and misfiring, a vehicle may enter a state of fail-safe mode; this is possible due to myriad failures of performance aspects of the engine.
• Control Failure: For controllers that should safeguard the vehicle or those inside, a fail-safe power system may be engaged to provide just the minimum level of operations necessary for fault detection.
• ECU or Data Network Problems: Modern vehicles are equipped with many data modules, also known as ECUs, that can communicate over a single data bus. If communication between them is disrupted, or one of the critical ECUs is mute, the vehicle will default into fail-safe mode.

All of the issues listed above have the potential to put the vehicle into fail-safe mode while at the same time reducing the power of the engine.

Is Driving Possible When The ‘Reduced Engine Power’ Warning Light Is On?

It is possible to continue driving your vehicle even when the ‘reduced engine power’ light is on. “Limp mode,” as it is referred to, is the maximum extent to which you should drive your vehicle, within reason.

The risk of driving in this mode is limited. However, driving the vehicle will not be a pleasurable experience because gas consumption is bound to be high, acceleration is bound to be weak, and on some vehicles, shifting may be rough.

Also, some vehicles may shut down optional supplementary features like the radio. In short, while it is possible to drive when the ‘engine power reduced’ indicator is illuminated, the vehicle should be towed if it needs to be driven more than a few miles.

Steps to Diagnosing & Fixing Reduced Engine Power

Thinking about the listed causes, the following steps should be taken to troubleshoot the issue and get on with driving:

• Stop the Vehicle: The first step after noticing a decline in the engine power while driving is to carefully pull over and stop the vehicle.
• Check Engine Light: Look for the check engine light and see if it is active or not. Flashing could indicate some more serious problems, in which case it is safer to call for roadside support.
• Restart Vehicle: First, stop the car and switch the engine off. Then wait for about 15-20 seconds before turning it back on. In some cases, these steps will reset the system and alleviate the problem.
• Check Fluid Levels: Ensure the recommended levels have not been exceeded or fallen short. In particular, insufficient engine oil or coolant can lead to further reduced engine power.
• Scan for Error Codes: An illuminated check engine light indicates the use of an on-board OBD-II scanner, which should be used to retrieve the relevant error codes.
• Inspect Throttle Body and Sensors: Ascertain that the throttle body and related components like the mass airflow sensor and oxygen sensors are free of any unclean or non-functional parts.
• Look for Exhaust Blockages: A malfunctioning exhaust system produces a powerful odor of sulfur. If you suspect a problem, have a mechanic check it.
• Seek Professional Assistance: If the diagnosis has been performed but the problems persist, don’t hesitate to take the car to your preferred automotive service shop.

With this sequence of steps, diagnosing and solving the problem independently should be straightforward! However, a competent mechanic should always be consulted as they will have the best experience and knowledge when it comes to properly diagnosing and troubleshooting the vehicle.

Make sure to not ignore problems such as reduced engine power. This could lead to further detrimental impacts for the vehicle and driving safety. Make sure you are keeping an eye out for these red flags and reacting to them on time.

Can I Fix My Reduced Engine Power Problem at Home?

Most of the time, the warning sign “reduced engine power” is displayed alongside a trouble code and within the vehicle’s computer memory. This can usually be traced to particular sensors and systems.

Do not jump to the conclusion that the parts or systems described by the DTCs are indeed faulty. It is also possible that the problem resides in the harness, circuit, connector or, indeed, some completely different system or component.

Engine control modules comprise an array of actuators and sensors. The alarming grounds offer groundless suspicion to many problematic wires or parts that comprise these actuators and sensors. Sometimes, bad engine grounds are the root cause of the problem. If so, the very first thing that must be done is to check the engine grounds, followed by the battery’s connections.

Decreased drivability issues will arise from drop voltages and currents due to a bad ground connection.

In bypassing the basics of removing the engine cover, use a digital multimeter to check the engine grounds. This will allow easy discovery of loose, corroded, or damaged connections affecting the system circuits, sensors, actuators, or any other components in the system.

In case of prior DTCs, check each component or circuitry as per the code that signifies before replacing any component, to check if it indeed needs replacement.

After checking the electronic components, before turning on the ignition and ensuring everything is correctly plugged in, ensure to:

• Check and clean all connectors for corrosion or dirt.
• Ensure all wires are properly secured within the harness connector.
• Confirm all solder joints towards each end of the wire are properly attached.

What Do I Do if the Problem is Too Difficult for Me to Solve Personally?

Most of the possibilities causing the reduced engine power for your vehicle are issues that need to be resolved urgently. Despite needing immediate attention, remain calm since all these complications are simple to fix with a bit of knowledge and guidance.

Whether or not you take your car to a repair shop will impact costs, but the advanced scan tools and equipment used will save you the hassle of spending additional time and energy in the future.

A mechanic’s work begins with scanning the vehicle and identifying the problem areas. After this step, you should receive an estimate for the necessary parts and labor required to complete the repairs.

What Should I Do If My Car Has No “Reduced Engine Power” Warning Light?

If no “reduced engine power” warning is present but you suspect the engine is running poorly, it is important to get to the root cause of the issue as fast as possible.

A more conservative approach would be to conduct a scan for diagnostics ahead of time.

It is extremely important to limit how often you use the vehicle until the repairs are made. Failing to do so will risk causing further damage and leading to more expensive repairs, which is not only reckless but highly unsafe.

Bear in mind that a single malfunction from one system could interconnect and cause issues across various systems. One single malfunction within your vehicle could trigger an error message that activates the ‘reduced engine power’ sign, which would lead to the triggering of other error messages within the machine’s control panel.

In case there are no apparent warning signs but you presume that the engine is operating under reduced capacity, you might want to check these components:

• Air Filter: An error code wouldn’t be generated due to an air filter getting clogged, but it is simple enough to be repaired and replaced.
• Fuel Pump: Fuel pumps tend to be more difficult to troubleshoot and expensive to replace. If the vehicle is functioning poorly or you are attempting to start the vehicle without warning lights illuminating, you might have to replace the fuel pump.
• Tire Pressure: Maintaining ideal tire pressure wouldn’t have a direct influence on the vehicle’s performance, however, low tire pressure can create friction on slick pavements, which would effectively impact driving experience.