Reduced Engine Power: Here’s What You Need to Know

From getting to work to getting the kids to school, you rely on your car in a vast number of ways. So when you step on the gas pedal and your vehicle’s engine responds sluggishly, of course this is major cause for concern when you’re experiencing reduced engine power.

In days-gone-by, this would have just meant changing the spark plugs or wires, changing out the rotor or distributor cap, and tweaking the carburetor. However, in today’s modern vehicles, there are all kinds of culprits behind your car’s hesitation to accelerate.

In this article, we will thoroughly explore what would cause reduced engine power, how to bypass reduced engine power, and how to fix reduced engine power. Read on to find out exactly what you need to know about why your car is behaving sluggishly.

What Does ‘Engine Power Is Reduced’ Mean?

In the world of automotive diagnostics, the ‘engine power reduced’ alert is a critical signal indicating that your vehicle’s computer system has detected a problem. This alert activates the vehicle’s fail-safe mode, known as “limp mode,” to prevent further damage.

In this state, your vehicle’s ability to accelerate diminishes, safeguarding the engine and ensuring your safety. Various issues can trigger this, ranging from minor sensor glitches to major part failures. Understanding this early warning can save you from costly repairs and keep you safe on the road.

Trouble Codes that Are Related to Reduced Engine Power

Depending upon what type of vehicle you own and the problem that is detected by the ECU, a certain trouble code will appear in the electronic control module’s (ECM) memory. Some of these trouble codes can include:

• P0120-P0124: This code points to problems with the pedal position or throttle position, or the circuit.
• P1125: These indicates a faulty system or component and may vary depending on the make and model of your vehicle.
• P1518: This points to a faulty system or bad system component and may vary depending on the make and model of your car.
• P2111: This code means that the throttle actuator control system is stuck open.
• P2135: This indicates a problem with the accelerator pedal position (APP), the throttle position (TP) sensor or switch, or the A/B voltage correlation.

The best way to properly diagnose and repair your vehicle is to take it into your local service shop and have it inspected by a certified mechanic.

What is Fail-Safe Mode?

The “engine power reduced” message is telling you that your vehicle has entered into a fail-safe mode. All modern cars are equipped with a fail-safe strategy to protect drivers.

Your car’s ECU may initiate a fail-safe mode to either protect the occupants inside of the vehicle or to prevent further damage to the car itself. When your car is in a fail-safe mode, there are a lot of different ways that your vehicle’s onboard electronics may limit its performance.

For example, if there is an issue with the electronic throttle actuator, the electronic control unit may decrease the maximum throttle opening. On the other hand, if there’s a concern with your car’s transmission, the electronic control unit may limit transmission operation to a particular gear range.

Some vehicles might display a dedicated message on your dashboard to give you a heads up that it is in fail-safe mode. In other instances, your “Check Engine” light may turn on.

Common Signs of Reduced Engine Power

Before the warning light appears, you can observe a few symptoms indicating reduced engine power. These signs may include:

• Diminished Acceleration: Your car struggles to pick up speed, especially noticeable on highways.
• Irregular Performance: The car might feel different, with erratic idling or trouble maintaining consistent speeds. It may also make more noise than usual.
• Decreased Fuel Efficiency: You may notice you’re filling up your gas tank more frequently than usual as the vehicle struggles to maintain its power.
• Check Engine Light: The check engine light might flash on before or along with the reduced engine power warning. It’s important to address this issue immediately and not ignore it.

These are just a few of the common signs. They’re not limited to any particular car, so no matter what vehicle you drive, it’s important to stay aware of your car’s performance and any changes that occur.

What Causes the “Reduced Engine Power” Message?

Asking what engaged reduced engine power warning message is somewhat like asking what turned on your check engine light—there are too many possibilities to list. 

Plus, GM has changed its fail-safe strategies over the years, so the problem that can engage the message depends on your ride’s year and model. 

Still, there are some problems that trigger the Engine Reduced Power message more often than others. Here are some of the issues that are best known for causing the warning to illuminate:

Electronic Throttle Actuator (Throttle Body) Problems 

One of the most common triggers is a problem with the electronic throttle actuator control (TAC) system.

Modern GM vehicles use this layout in place of a traditional, mechanical throttle body and linkage. The technology was first introduced on the 1997 C5 Corvette.

In the TAC system, the PCM monitors two accelerator pedal position (APP) sensors to determine the driver’s desire for acceleration. Then, the device calculates the appropriate throttle response from a pair of throttle position (TP) sensors.

Once the module has the necessary information from the sensors, the PCM uses an actuator motor (integrated into the throttle body) to operate the throttle, thereby controlling airflow into the engine.

When the throttle body fails or becomes dirty, it can trigger Reduced Engine Power mode.

Bad Pedal Position Sensor

A problem anywhere in the TAC system can easily trigger the Reduced Engine Power warning on the dash. For instance, the problem could be one (or both) of the APP sensors, which are usually integrated into the accelerator pedal.

Faulty Throttle Position Sensor

The other primary input to the TAC system is a pair of TP sensors. When one (or both) of the sensors goes bad, the vehicle will enter Reduced Engine Power Mode.

These problems are often caused by accumulated dirt or failure in the throttle body, which affects airflow to the engine. A faulty or dirty sensor may send incorrect data, which leads to unpredictable engine behavior and reduced power.

Circuit Issues

Circuit issues, such as damaged wires and poor connections, can prevent the TAC system from operating properly. This can cause an array of problems, including a vehicle that enters Reduced Engine Power mode.

PCM or Data Network Problems

Most late-model vehicles contain dozens of computers (also known as modules) that communicate with one another over a data network.

If the network gets interrupted, or the PCM is having issues, the vehicle may enter Reduced Engine Power mode.

Idle Relearn Procedure Needed

On many GM vehicles, an idle relearn procedure is required whenever the throttle body is cleaned or replaced. Failing to do so can result in the vehicle entering Reduced Engine Power Mode.

Cooling System Issues

Some GM vehicles will enter Reduced Engine Power Mode when the engine begins to overheat due to cooling system issues. The PCM triggers the mode to protect the engine from further damage.

To prevent this, ensure all fluids are at the recommended level. Low engine oil or coolant may trigger this warning.

Engine Performance Problems

In some instances, the Reduced Engine Power warning may illuminate to inform the driver that the vehicle lacks power due to an underlying condition.

For example, a faulty high-pressure fuel pump might reduce engine power, thereby causing the warning to illuminate.

Diesel Engine Performance Problems

If you’ve got a Duramax diesel, the Reduced Engine Power warning could Illuminate for a variety of reasons.

There are many different technical service bulletins (TSBs) for Duramax-powered vehicles that mention Engine Reduced Power mode. Each document lists something different—ranging from a damaged MAP sensor connector to an air intake leak—as being a potential cause.

Loose Connection

Wires connect crucial car parts, so if there’s a problem with them that’s affecting engine performance, the PCM could trigger the Reduced Engine Power warning.

Wire issues that can trigger the warning light range from a loose clamp to damaged connections. Some of them are easy to identify and fix, while others require a full system inspection to pinpoint and repair.

Faulty Alternator

A failing alternator can’t supply enough electricity to the engine, causing it to shutdown. That, in turn, could trigger Reduced Engine Power warning.

Low Voltage Batteries

When the car battery is nearly drained, it can’t send enough energy, which reduces engine performance. That can trigger the Reduced Engine Power warning.

The engine will operate until the battery drains and the diminished energy supply cuts off.

What Causes Fail-Safe Mode?

Just like with your “reduced engine power” light coming on, there are a number of reasons why your car could enter into a fail-safe mode. Here are some of the most common reasons:

• Automatic Transmission Troubles: Issues with your vehicle’s transmission or the electronic controls can cause its transmission to default to a fail-safe mode. This is often called “limp mode.” Generally, in this state, the transmission line pressure increases and the unit defaults to a particular gear.
• A Faulty “Drive-By-Wire” System: Today’s modern vehicles have what is known as a “drive-by-wire” system that replaces the traditional mechanical components with intricate electronics. In many instances, if an issue arises in one of these systems, the ECU must limit performance to keep the vehicle, the driver, and the passengers safe.
• 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: Corroded, damaged, or loose wires can inhibit your vehicle’s onboard electronics from properly functioning. This can cause a plethora of problems, including a vehicle that goes into the fail-safe mode.
• Engine Performance Troubles: An array of engine performance issues, including overheating and misfiring, can cause your car to enter into a fail-safe mode. 
• Faulty Sensors: Obviously, not all faulty sensors will send your vehicle into a fail-safe mode. However, some sensors that are integral to protecting the vehicle and/or its occupants can trigger the car to go into a fail-safe mode.
• ECU or Data Network Problems: Late model cars contain many ECUs, or modules, that communicate with each other via a robust data network. If this network somehow gets interrupted, or if one of the vital ECUs can’t communicate, your car may enter into a fail-safe state.

Any of these problems can cause your car to enter into a fail-safe mode, and also reduces engine power.

Can I Drive My Car with the “Reduced Engine Power” Warning Light On?

Driving your vehicle while the “reduced engine power” light is on is possible. However, this feature is known as “limp mode,” which is as much as you should operate your car, within reason.

There aren’t many risks to driving in this mode. But the car won’t be a pleasure to drive, as gas mileage will be excessive, acceleration will be poor, and on some vehicles, shifting gears will be jerky at best.

Additionally, some cars may disable non-essential accessory components, such as the radio. The short answer is that while it is possible to drive when your “reduced engine power” light in on, you should get your car towed if it must travel further than a couple of miles.

Steps to Diagnosing & Fixing Reduced Engine Power

With the common causes in mind, when you encounter reduced engine power while driving, follow these steps to troubleshoot and get back on track:

1. Pull Over: Once you realize that your engine’s power has been reduced, the first thing to do is to pull over safely and stop the vehicle.
2. Check Engine Light: Check whether or not your check engine light is on as well. If it’s flashing, it may be a sign of a more severe issue, and it’s better to call for roadside assistance.
3. Restart the Vehicle: After stopping the car, turn off the engine and wait for 15-20 seconds before restarting it. Sometimes, this can reset your vehicle’s computer system and temporarily resolve the issue.
4. Check Fluid Levels: Make sure all fluid levels are at the recommended levels. Low engine oil or coolant can also trigger reduced engine power.
5. Scan for Error Codes: If the check engine light is on, use an OBD-II scanner to read any error codes and identify the problem.
6. Inspect Throttle Body and Sensors: Check the throttle body for cleanliness and functionality. Also, inspect the mass airflow sensor and oxygen sensors for any damage or issues.
7. Look for Exhaust Blockages: A strong sulfur smell can identify a clogged catalytic converter. If you suspect this is the issue, have it checked by a mechanic.
8. Seek Professional Assistance: If the issue persists, it’s best to seek professional help from a trusted automotive service shop.

This list of steps will help you identify the issue and potentially resolve it on your own! If not, be sure to seek help from a trusted mechanic, as they have the experience and knowledge to properly diagnose and repair any issues with your vehicle.

Don’t ignore reduced engine power, which can lead to further damage or unsafe driving conditions. Stay vigilant and address any warning signs immediately! 

Can I Fix My Reduced Engine Power Problem at Home?

Typically, your vehicle’s “reduced engine power” light will appear with a DTC in its computer’s memory that points to an issue in a specific sensor or system.

However, do not immediately assume that something is problematic with a specific part or system described by the DTCs. The fault can also be with a harness, circuit, connector, or even an entirely different component or system.

Bad engine grounds are sometimes to blame for many apparently problematic wires or parts that connect the numerous actuators and sensors to the electronic control module (ECM). So, you initially need to check the condition of the engine grounds, including battery connections.

A bad ground connection will cause currents and voltages to drop, leading to all kinds of drivability concerns.

Use a digital multi-meter to properly check the engine grounds. This will make it simple to detect damaged, corroded, or loose connections that may be afflicting the sensors, system circuits, or actuators.

If you find any DTCs, test the specific components or circuit that the code points to before actually replacing it, to ensure that it is faulty.

When checking the electronic components, be sure to turn off the ignition switch, then:

• Unplug the connector and check for corrosion or dirt.
• Pull at the wires on the harness connector to check for loose ones.
• Check the connections on both ends of the wire to verify good connections.

What Do I Do if I Can’t Fix the Reduced Engine Power Problem Myself?

Many of the issues that could cause reduced engine power in your vehicle are problems that need to be addressed right away. However, you should not panic, since many of these issues can be easily repaired with some basic know-how and a bit of research.

Taking your car to a repair shop can be pricier than making the repairs yourself, but the benefit of their innovative scan tools and readily available equipment will save you a lot of time and headache down the road. 

The mechanic will run a full and thorough scan of the car before doing any work on it to pinpoint the exact location of the problem. After that is completed, you should receive a quote for parts and labor.

 What Should I Do if My Car Doesn’t Have a “Reduced Engine Power” Warning Light?

If your vehicle does not have a “reduced engine power” warning light yet you can feel that the engine is running poorly or goes into limp mode, you should do your best to immediately find out what is wrong with it.

You can also preemptively run a scan on the car if you anticipate an issue could arise.

It’s critical that you drive the vehicle minimally until the issue is resolved. Otherwise, it could further damage the car and lead to costlier repairs. It is also unsafe.

Keep in mind, that it can only take one issue with a single system to spill over into other systems too. An error code that triggers the “reduced engine power” light could also trigger additional error lights within your car’s gauge cluster.

If you think that your car is operating on reduced power, and there are no warning lights that are illuminated, you can check the following components, including:

• Air Filter: A clogged air filter won’t generate an error code, and can easily be repaired and replaced.
• Fuel Pump: Fuel pump troubles can be tougher to diagnose and can be pricey to replace. If your car is running poorly, or you’re trying to start it but are unable to, and there are no warning lights on the dashboard lit up, you may need to replace the fuel pump.
• Tire Pressure: Low tire pressure in and of itself will not cause your car to operate poorly, but it can cause friction on slick roadways. This may cause a noticeable difference in your driving dynamics.