DIY

Reduced Engine Power Mode: What Does it Really Mean?

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Is your Chevy or other General Motors (GM) vehicle displaying “Engine Power Reduced” on the instrument cluster? Maybe the check engine light is on as well? Don’t panic and trade-in your car just yet—there may be a relatively easy (and affordable) remedy for your concern.

What Does the “Engine Power Reduced” Warning Light Mean?

If you’ve got the owner’s manual to your GM vehicle (Chevy, Buick, etc.) handy, you can flip to the section about the driver information center (or instrument cluster). There, you’ll find a general overview of what the Engine Power Reduced message means.

But in case you’ve misplaced your owner’s manual—or it’s buried under a mound of junk in your glove box—we’ll explain the message here as well. The Engine Power Reduced warning indicates that your car’s performance has been limited to avoid damaging the engine. Your car’s computer, often known as an electronic control unit (ECU), triggers Reduced Power Mode when it detects a system failure.

In other words: The Engine Power Reduced message is GM’s way of telling you that your car has entered a fail-safe mode.

GM’s Reduced Power Mode can inhibit your vehicle’s ability to accelerate. Even if power isn’t reduced immediately, performance may be limited the next time you go to drive the car. In some instances, the ECU may actually cut off fuel delivery to the engine, rendering the vehicle undrivable.

Your car’s computer, often known as an electronic control unit (ECU), triggers Reduced Power Mode when it detects a system failure. In other words: The Engine Power Reduced message is GM’s way of telling you that your car has entered a fail-safe mode.

What Causes the Reduced Engine Power Message?

Asking what engaged reduced engine power mode is 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 exactly what can engage the message depends on the year and model of your vehicle.

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.

In the TAC system, the ECU monitors two accelerator position sensors to determine the driver’s desire for acceleration. Then, the device calculates the appropriate throttle response from a pair of throttle position sensors. Once it has the necessary information from the sensors, the ECU uses an actuator motor to operate the throttle, thereby controlling airflow into the engine.

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 of the sensors, the throttle body, or even the accelerator pedal assembly.

Although a problem in the TAC system is one of the most common reasons a GM vehicle might enter reduced power mode, there are countless other possibilities. For example, some model 2002-2005 year Chevy, Buick, Oldsmobile, and GMC SUVs will display the message due to a faulty electronic fan clutch. Other vehicles may turn on the warning due to a problem with the fuel system—the list goes on and on.

Basically, whatever could trigger a fail-safe mode could cause the Reduced Engine Power warning to pop up on the dash. So, you can’t just throw parts at the car in an attempt to turn off the message. You’ll need to retrieve the corresponding diagnostic trouble codes, then follow up with some troubleshooting steps.

Fail-Safe Mode

The message “Engine Power Reduced” is GM’s way of telling you that your car has entered a fail-safe mode—but GM isn’t the only automaker to equip its vehicles with a fail-safe mode. In fact, all modern cars have some type of fail-safe strategy built into them.

The ECU may initiate a fail-safe mode to prevent vehicle damage and/or protect the occupants inside the car. When in a fail-safe mode, there are different ways your car’s onboard electronics may limit performance. For instance, if there’s a problem with the electronic throttle actuator, the ECU may reduce the maximum throttle opening. On the other hand, if there’s a problem in the transmission, the ECU may limit transmission operation to a certain gear range.

Sometimes, the vehicle will display a dedicated message on the instrument cluster to let you know it’s in a fail-safe mode. For example, as previously mentioned, late model GM vehicles often display an “Engine Power is Reduced” message on the instrument cluster.

In other cases, the car may simply turn on the check engine light without displaying a dedicated fail-safe mode message. Also, when the transmission goes into limp mode, you may see a “Transmission Malfunction” warning—or something similar—on the dash.

What Causes Fail-Safe Mode?

There are many reasons a vehicle may enter a fail-safe mode. To know for certain, you’ll have to do some troubleshooting of your own (see the following section on troubleshooting). If you want a broad picture, however, here are some of the most common reasons a vehicle may enter a fail-safe mode.

1. Automatic Transmission Problems

Problems with the transmission or its electronic controls can cause the transmission to default to a fail-safe mode. This is often referred to as limp mode. Typically, in this state, the transmission line pressure is increased and the unit defaults to a certain gear.

Keep in mind, however, that other fail-safe strategies may be used instead. For example, the ECU may turn off the fuel injectors on a couple of cylinders to reduce engine torque, thereby protecting the transmission.

2. Faulty “Drive-By-Wire” Systems

Most modern cars have what are referred to as “drive-by-wire systems” that replace traditionally mechanical components with complex electronics. In many cases, if a problem occurs in one of these systems, the ECU must limit performance to keep the vehicle and its occupants safe. One primary example is the electronic throttle actuator system that was mentioned earlier.

In some instances, a weak battery can inhibit the performance of various electronics, causing the vehicle to enter a fail-safe mode.

3. Charging System Issues

Late model vehicles have a plethora of electronics that rely on battery power. In some instances, a weak battery can inhibit their performance, causing the vehicle to enter a fail-safe mode.

An overcharging or undercharging alternator can trigger such a mode as well.

4. Damaged or Faulty Wiring

Damaged, corroded, or loose wiring can prevent your car’s onboard electronics from working properly. This can cause an array of problems, including, in some instances, a vehicle that enters a fail-safe mode.

5. Engine Performance Problems

A variety of engine performance problems—ranging from misfiring to overheating—can cause a vehicle to enter a fail-safe mode. Once again, exactly what triggers the mode depends on the type of car you’re dealing with. Different automakers implement different fail-safe strategies into their vehicles.

6. Bad Sensors

Obviously, not all bad sensors will cause your car to go into a fail-safe mode. Oftentimes, engineers design a car so that the ECU can approximate vital signals in the event that an important sensor fails. However, there are instances where problems with a sensor that’s integral to protecting the vehicle or its occupants can trigger a fail-safe mode.

7. ECU or Data Network Issues

Most late model vehicles contain dozens of ECUs (also known as modules) that communicate with one another over a data network. If the network gets interrupted, or if one of the vital ECUs cannot communicate, the vehicle may enter a fail-safe mode.

Troubleshooting Fail-Safe Modes

Potential causes for entering a fail-safe mode vary by vehicle. If you’re troubleshooting a car that’s in a fail-safe mode, the first thing you’ll want to do is check for diagnostic trouble codes (DTCs) with a scan tool or code reader. DTCs can point you in the right direction for further diagnostics.

Keep in mind that codes aren’t a complete diagnosis—but they will tell you where to begin your analysis.

It’s also a good idea to consult the factory repair information before digging in too deep. As was mentioned, exactly what causes a fail-safe mode varies depending on the year, make, and model of your vehicle. If you don’t research your particular application beforehand, you may end up chasing your tail.

Checking technical service bulletins (TSBs) can also be very helpful. ALLDATA has single-vehicle subscriptions for DIYers that provide detailed factory repair information. Many technical service bulletins (TSBs) are listed there, too.

Can I Drive in Fail-Safe Mode?

Technically, you can (usually) drive slowly when in a fail-safe mode—or when engine power reduced is illuminated on the dash. However, doing so is not recommended. It is best to tow your vehicle to the nearest repair facility, as driving at extremely low speeds can be dangerous. Not to mention, your vehicle is in a fail-safe state because something is wrong, and pushing it further could cause additional damage.

Also, there are instances where a vehicle will shut off completely after entering a fail-safe mode. Then, you’ll have no choice but to tow it in for repair.

Limp Mode

The term limp mode is often used interchangeably. Sometimes, automotive professionals use the term to describe a general fail-safe mode. In other instances, it’s used solely to describe a default state the vehicle enters to protect the automatic transmission.

To summarize…

The Engine Power Reduced message is GM’s way of indicating your car has entered a fail-safe mode. Unfortunately, there’s no magic bullet for this concern—and you’re not going to find a guaranteed fix via a Google search.

Although GM’s engine reduced power mode is often triggered by a problem in the TAC system, that’s not always the case. So, if you’re seeing the Engine Power is Reduced message on your dashboard, you’ll need to check for diagnostic codes and do some research—or pay a visit to your mechanic ASAP.

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Author

Mia Bevacqua

Chief Mechanic at CarParts.com

Mia Bevacqua is an automotive expert with over 15 years of industry experience. She holds ASE Master, L1, L2, and L3 Advanced Level Specialist certification, as well as a bachelor's degree in Advanced Automotive Systems.

Throughout her career, Mia has applied her skills toward automotive failure analysis inspections, consulting, diagnostic software development, and of course, freelance writing. Today, she writes for companies around the world, with many well-known clients showcasing her work.

Mia has a passion for math, science, and technology that motivates her to stay on top of the latest industry trends, such as electric vehicles and autonomous systems. At the same time, she has a weakness for fixer-upper oddballs, such as her 1987 Chevy Cavalier Z-24 and 1998 Chevy Astro Van AWD.