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

Reduced Engine Power

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. 

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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 Reduced Engine Power Mean?


If your car isn’t accelerating properly, your “engine power reduced” warning light may also be illuminated on your dashboard. The “check engine” light may have popped on as well. Don’t panic just yet! We’ll go over everything you need to know about this problematic occurrence to ease your concern.


Typically, the “engine power reduced” warning light on your dash means that your vehicle’s performance has been reduced to avoid damaging its engine. The computer in your car, also known as its “electronic control unit” (ECU) has triggered the Reduced Power Mode after it has detected a system failure.


In other words, the illuminated “engine power reduced” light is your vehicle’s way of telling you that it has entered into a fail-safe mode. 


This can inhibit your vehicle’s ability to properly accelerate. Even if the car’s power isn’t immediately reduced, its performance may be limited the next time you drive it. In some cases, the car’s ECU may even cut off all fuel delivery to its engine, rendering your vehicle un-drivable.


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.


What Causes the “Reduced Engine Power” Light to Go On?


Asking why your car’s “reduced engine power” light came on is a lot like asking why your “Check Engine” light is illuminated. There is a myriad of possibilities to list. 


However, one of the most common causes of this issue is a problem with your car’s electronic throttle actuator control (TAC) system. A lot of modern cars utilize this layout in lieu of a traditional, mechanical throttle body and linkage.


In a throttle actuator control system, the ECU oversees two accelerator position sensors to determine your desire to accelerate. The device than calculates the appropriate throttle response from two throttle position sensors. Once it has gleaned the necessary information from the sensors, the ECU uses an actuator motor to maneuver the throttle, thus controlling airflow into your car’s engine.


An issue with your throttle actuator control system can easily trigger the “reduced engine power” warning light on your dashboard. For example, the issue could be the throttle body, one of the vehicle’s sensors, or even the accelerator pedal assembly.


Although an issue with your car’s throttle actuator control is one of the most common reasons for it to enter into a reduced power mode, there are numerous other possibilities. For instance, some cars will display the “reduced engine power” message because of a faulty electronic fan clutch. Other cars may turn on this message because of an issue with the fuel system. And the list goes on and on.


Some other issues that may lead to a reduction in engine power in your vehicle could include:


  • A Loose Clamp, Wire, or Harness: Your car is brimming with connectors and wires that power all of its components and make it run. A short in the electrical system, a loose ground wire, or a loose clamp can trigger an issue with your vehicle.


  • Failing Oxygen Sensors: A car’s oxygen sensors measure the amount of oxygen that is exiting the vehicle through the exhaust system. They also help to adjust the air-fuel mixture for proper combustion. If one of them is faulty, your “reduced engine power” light may come on, in addition to the “check engine” light.


  • An Issue with the Throttle Body: Your car has a butterfly valve that opens and closes within its throttle body to enable air to enter the engine. If this valve is damaged, it could trigger your car’s “reduced engine power” light to illuminate.


  • A Bad Mass Airflow Sensor: Another sensor within your car is the mass airflow sensor. It is located between the intake manifold and the air filter. Its job is to measure things like air pressure and density entering a direct injection engine. Additionally, it tells the computer how to deliver and mix the fuel with the incoming air to provide superior combustion within the engine.


  • The ECU is Faulty: If there is a problem with your car’s ECU, it could be one of the most dire and costliest issues that will cause the “reduced engine power” light to pop on.


  • The Catalytic Converter May Be Clogged: This component of your car is mounted underneath the vehicle after the exhaust manifold. It converts carbon monoxide into carbon dioxide through oxidation and reduction, vastly reducing harmful emissions into the air. 


  • Battery Issue: In many cases, a battery problem, will not cause the “reduced engine power” light to come on. However, it can still cause your “engine check” light to illuminate.


  • There’s a Problem with the Transmission: Another problem that will most likely trip the “check engine” light prior to triggering the “reduced engine power” message is a transmission fault code. These can include a slipping clutch or low transmission fluid.


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.


What Should I Do if the “Reduced Engine Power” Light Comes On?


If you are behind the wheel and the “reduced engine power” light pops on, the very first thing that you should do is try your car back home or to a repair shop right away. If you’re already at home, don’t attempt to drive the vehicle.


Known Issues Causing Reduced Engine Problems in Specific Models


If your “reduced engine power” light is on, and you drive one of these specific types of vehicles, here are some of the known causes behind your car’s acceleration issues:


GM Models with Throttle Assembly Issues: Some GM vehicle models have been known to suffer from reduced engine power troubles due to a fault afflicting their throttle assembly. Typically, you will be warned by a DTC P2135 message along with the general “reduced engine power” light on your dashboard.


The models listed below fall into this category:


  • Chevy TrailBlazer made between 2008 and 2009
  • Chevy Tahoe Two-Mode Hybrid made between 2008 and 2011
  • Chevy Silverado Two-Mode Hybrid made between 2009 and 2011
  • Cadillac Escalade Two-Mode Hybrid made between 2009 and 2011
  • GMC Envoy made between 2008 and 2009
  • Hummer H2 made between 2008 and 2009
  • Hummer H3 made between 2008 and 2010
  • GMC Canyon, Sierra, Sierra Denali, Yukon, Yukon Denali, Yukon XL, and Yukon XL Denali made between 2008 and 2011
  • Chevy Avalanche, Express, Colorado, Silverado, Suburban, and Tahoe made between 2008 and 2011
  • Cadillac Escalade, Escalade ESV, and Escalade EXT made between 2008 and 2011
  • GMC Sierra Two-Mode Hybrid made between 2009 and 2011
  • GMC Yukon Two-Mode Hybrid made between 2008 and 2011


The types of engines affected include:


  • L94, L20, LY5, LC9, LMG
  • L76, LH8, LH9, LS2, LZ1
  • L96, LH6, L9H, LY6, RPO
  • LMF, LFA, LY2, L92


If your GMC vehicle is one of the makes and models discussed above and it is suffering from reduced engine power, have a GM certified mechanic look at it right away.


Ford F-150 Charge Air Cooler: Similar complaints that were investigated by the National Highway Traffic Safety Administration found that Ford F-150 trucks made between 2001 and 2013 that were equipped with a 3.5-liter, turbocharged direct injection engine would suddenly experience reduced engine power while operating at highway speeds.


Company service bulletins indicated that the charge air cooler (CAC) was the cause behind this. This is because it could accumulate moisture while the truck was cruising at highway speeds for a period of time under humid conditions. 


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.


Frequently Asked Questions


How Do I Reset the ‘Reduced Engine Power” Light


Much like your car’s “check engine” light, its “reduced engine power” message can’t simply be reset with a push of a button. To get the message to go off, you (or your mechanic) will need to fix the underlying issue that triggered the light to go on in the first place.


Can Low Oil Reduce My Car’s Engine Power?


Sometimes, low oil can lead to a lack of acceleration. For instance, modern engines have variable valve timing (VVT) systems that rely heavily on oil pressure to operate. 


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Wrapping It Up


There are many things that can cause reduced engine power in your vehicle. If your “reduced engine power” light comes on, do not drive your car. You can try to repair it by yourself at home, or take your vehicle to a certified mechanic to get fixed. 

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