Reduced Engine Power: What Causes It? And How Can I Fix It?

Car Driving on Highway

Nowadays, it feels like modern vehicles have become more like driving computers than actual cars or trucks. They’re incredibly technologically advanced, with computers and sensors controlling just about every aspect of your driving experience.

All of this is designed to make driving as easy, safe, and convenient as possible. However, any error that disturbs the balance between each sensor or module can cause a fault in your drive system and could result in an error light.

Some can be particularly unnerving, especially the reduced engine power light, which is what we’re going to be discussing in detail throughout this article.

An engine should run in a specific way. If it isn’t performing as it should be, it’ll probably be pretty obvious to you. Just in case it isn’t, though, the reduced engine power light lets you know when something isn’t right.

In the following sections, we’re going to discuss why reduced engine power is bad, why that light is so important for you and your vehicle, and how you can take steps to either fix it yourself or have a professional mechanic fix the problem for you.

How Can I tell When My Vehicle Is Running On Reduced Engine Power?

You live with your car almost every day, so you’re most familiar with how it functions under normal circumstances.

For starters, your familiarity with it will probably be the best indicator if you’re running on reduced engine power, even if there aren’t any warning lights displayed in your gauge cluster.

However, just in case you don’t pick up on a problem, your car will. After all, not everyone’s an expert that knows what they need to look out for.

The computers and sensors that make your vehicle run are programmed with a backup setting, sometimes called “limp mode” or “safe mode”, which will automatically decrease your vehicle’s power to try and prevent damage to the engine.

This backup setting can shut down accessories, slow down your speed or even completely disable your vehicle depending on your vehicle.

Most vehicles will provide enough power to drive to the shop or home in most cases. However, there may be an unexpected problem.

What Exactly Does the Reduced Engine Power Light Mean?

The reduced engine power light comes on when the vehicle’s computer detects a fault in any of the systems that allow the engine to run optimally, such as airflow sensors, throttle sensors and oxygen sensors.

This light isn’t found in all vehicles out there, nor is it always a light in the vehicles that do have this warning mechanism.

If your vehicle has one, you may see the warning on your gauge cluster’s screen.

This light is often found on General Motors vehicles. Other vehicles, especially luxury and performance vehicles, don’t have this warning light, but do have a “limp home” mode.

It should be fairly obvious if a vehicle enters “limp mode” as discussed above, especially if the check engine light is displayed and your vehicle is severely limited in power and capability.

What Should I Do If The Reduced Engine Power Light Comes On?

If you’re driving and the reduced engine power light comes on, the first thing you should always try to do is get the vehicle back home or to a shop immediately. If you’re already at home and the light comes on, don’t drive the vehicle.

Once the light goes on, you should have your vehicle scanned using an OBD II scan tool.

The vehicle’s computer modules store any errors and faults. This is true regardless of whether the light turns on or off.

Back in the day, older vehicles didn’t have the computer systems that newer vehicles do now. As technology grew in the 1980’s and 90’s, scanning a vehicle was possible, but didn’t always produce specific and accurate results as to the error. It could also prove to be extremely costly.

In 1996, the EPA required that all vehicles have OBD II compatible software. This was in addition to expensive or manufactured scan tools. OBD stands for “onboard diagnostics”, and OBD II standardized all the information your vehicle stores.

If you don’t have an OBD II reader, you can usually go to an auto parts store and they will scan your vehicle for free. If you do own an OBD II reader you will be able to see the errors.

They usually range from about thirty dollars to thousands of dollars, depending on the scanner’s capabilities.

What Might Cause The Reduced Engine Power Light To Come On? And How Can I Fix Is it?

You should be concerned about the many possible reasons your engine power light may come on.

It shouldn’t take long to scan your vehicle. Especially if you use a high-quality scanner tool.

There’s a Loose Wire, Harness, or Clamp

Your vehicle is full of wires and connectors that power everything and make it run. Your vehicle can be affected by a short circuit, loose ground wire, and loose clamp.

If this happens, it is the most obvious and easiest to fix. However, if nothing is loose, no wires are exposed or broken and everything is correctly hooked up, you’ll more than likely need to consult a professional mechanic.

What Should I Do to Fix This?

Whenever you’re dealing with a vehicle’s electric systems, be sure to disconnect the battery first before fiddling with any wires or sensors.

Verify that all connections have been made. You should inspect for unhooked wires and grounds. You should inspect for any damaged or exposed wiring.

Reconnecting anything that’s loose can usually be easily done, but any exposed or damage wiring will need to be replaced.

Oxygen Sensors Are Failing

Oxygen sensors measure the amount of oxygen exiting the vehicle through the exhaust system.

They help in proper combustion by adjusting the air/fuel mixture. One of these lights will be illuminated if it is defective.

What Can I Do to Fix This?

At the very least, you can attempt to clean your oxygen sensor, but if this doesn’t work it may need replacing.

Modern cars have at least two oxygen sensors. Some vehicles have eight. An OBD II scan will help you identify which sensor is causing the problem.

Replacement oxygen sensors aren’t too expensive – they may cost up to about $500 – but most replacements require a special tool to complete the job. This tool is essentially a special wrench and is relatively inexpensive, but most people don’t have one.

It is possible to clean your oxygen sensor. You can also buy an oxygen sensor replacement online and have it installed by a mechanic. This will reduce the cost of replacement, at least in part.

The Throttle Position Sensor is Faulty

The throttle position sensor is usually located within the throttle body near the butterfly valve that opens up to allow air into the engine.

This sensor measures your position on the accelerator pedal when you press the gas. It tells the computer how far to open the valve so that the engine can breathe.

This sensor aids in transmission shifting when air enters the engine. If this sensor can’t communicate with the vehicle’s computer systems to regulate engine revving, the vehicle will go into limp mode and trigger the reduced engine power light.

What Can I Do to Fix This?

The throttle body sensor, similar to the oxygen sensor, isn’t exactly an incredibly costly fix, nor is it an inexpensive one. The cost of a new sensor depends on the car model and make. It can run anywhere from $100-$500.

You can replace the sensor yourself if you are a skilled DIYer. However, it is more common to have the sensor and the throttle body replaced by a professional.

You can purchase a replacement sensor at the minimum to avoid any price gouging.

A Throttle Body Issue

The throttle body is comprised of more than just the throttle position sensor.

To allow air to flow into the engine, a butterfly valve is located within the throttle body. The warning light may be activated if the valve is broken or damaged.

The warning light may also be activated if carbon buildup in the engine causes the engine to believe that less air has been received.

What Can I Do To Fix This?

Generally speaking, it’s easier to just replace the entire throttle body altogether, rather than each individual piece of it. Replacement throttle bodies are usually between $100 and $200, including labor.

However, you may not have to replace the throttle body. It is worth your time to clean the throttle body yourself before spending any money. It is possible to fix air restriction caused by dirt and soot.

The process of replacing the throttle body is simple and easy, even if it requires you to do so.

The Mass Airflow Sensor is Faulty

The mass airflow sensor is located between the air filter and intake manifold.

It monitors air density and pressure in direct injection engines and informs the computer how to mix fuel and incoming air for optimal combustion.

What Can I Do to Fix This?

You can clean the mass-airflow sensor, just like the throttle body. Sprays are now available to clean the MAF.

Although a replacement may cost a few hundred dollars it is usually less than a throttle body, oxygen sensor or throttle body.

It’s also not a must for you to have a professional work on this for you. It is easy to replace the ECU yourself, thanks to the many online tutorials and charts.

The Vehicle’s ECU is Faulty

The ECU, short for Engine Control Unit, is the computer with which all of these sensors communicate. It controls almost all aspects of how a car operates and will also compensate for abnormal conditions in the engine.

An ECU problem can cause the engine light to go out when it is not working properly. This is one of the most expensive and serious problems.

What Can I Do to Fix This?

Unfortunately, because the ECU is essentially a computer, the only real way to tell if it’s causing the warning light is to run a scan with an OBD II scanner.

A replacement ECU can be purchased, but may need tuning or a re flash to make it work properly with your vehicle and environmental factors.

If you’re not confident in your computer skills and tuning abilities, it is best to have this done by a professional mechanic.

The Catalytic Converter is Clogged

The catalytic converter is mounted underneath the vehicle after the exhaust manifold. It is responsible for converting carbon monoxide to carbon dioxide by reduction and oxidation. This reduces harmful emissions.

It is illegal to drive a car with no catalytic converter as of today (except if it is pre-1975). If it gets clogged, it will fail an emission test.

This could trigger the lower engine power warning light but it’s more likely to cause the check engine lamp.

What Can I Do to Fix This?

Like the ECU, a catalytic converter replacement is a costly repair because of the way it’s made and the materials used. A new one can cost over $2000, plus labor.

A tech-savvy DIYer can replace the catalytic convert without too much difficulty. However, you will need a jack stand as well as other tools to access the vehicle.

There’s a Battery Problem

In most cases, a battery problem – be it a dead/damaged cell or a loose ground – won’t cause the reduced engine power light to come on.

You will probably see other signs of a battery problem before the warning light goes on.

What Can I Do to Fix This?

It is important to ensure that all connections are secure and not corroded.

To remove corrosion from the terminals, disconnect any cables and use baking soda or another cleaner.

The inability to start your car if the battery cells have become dead or damaged will alert you sooner than a warning light.

Most batteries can be replaced with replacements, which are often inexpensive. Though charging your battery might be all that’s needed. A dedicated battery tester with diagnostic features is the best way to find out how healthy your battery is.

And To determine if your car needs a new battery, please refer to this guide on car battery types, groups, and sizes.

There’s a Fault in the Transmission

Another issue that will most likely trip the check engine light before the reduced engine power light is a transmission fault code.

The sensors that we’ve discussed so far are so closely linked to correct transmission operation that a decreased engine power can be caused by the transmission and any of its systems.

A fault code could be triggered by low transmission fluid or a slippage in the clutch.

What Can I Do to Fix This?

You can check the transmission fluid yourself by referring to your owner’s manual or by following our guide on how to check and add transmission fluid. You will need to locate the dipstick and check the fluid quality and level. This is similar in nature to checking the engine oil.

Replacing the transmission fluid may sometimes fix the issue, but this is unlikely to solve the problem since it’s usually a more serious issue going on.

An engine scan will provide additional information regarding the transmission problem.

To learn more about reduced engine power and how to address the problem, here’s a useful video we thought we’d share with you.

What Should I Expect If I Can’t (Or Don’t Want) To Fix My Vehicle Myself?

A lot of causes of a low engine power warning lamp need to be addressed right away. However, this shouldn’t be a cause for panic, since most of these issues can be repaired with a little research and some basic know-how.

While it will be more expensive to take your vehicle to a mechanic than doing the repairs yourself, the benefits of their advanced scan tools will help you save time and avoid any potential mistakes.

To pinpoint the problem, any mechanic will do a thorough scan of your vehicle. If you want to be involved with what’s going on, you can always request that the mechanic show you the error codes presented by the ECU and an explanation of each.

After that’s done, you should receive a quote for parts and labor.

A second opinion is always possible if any of the above is not satisfactory. With that being said, it should be noted that most mechanics will charge a small fee for performing an initial scan.

What Do I Do If My Vehicle Doesn’t Have a Reduced Engine Power Warning Light?

In vehicles that don’t have a reduced engine power warning light, and you can feel that the engine is running poorly or goes into limp mode, you should do your best to find out what the problem is as soon as possible.

If you suspect or sense a problem, you can preemptively scan your vehicle.

When your vehicle detects a problem related to engine power, it will decrease the driving system’s capability.

It is important that the vehicle is not driven beyond its limits until the problem is fixed. If damage is not addressed quickly, costly repairs may be required.

Remember that a single issue in one system can cause other issues. A code that causes the reduced engine power light to turn on may also cause other errors in the gauge cluster.

The following components can be checked if you suspect your vehicle is running on less power.

If any of these are culprits, you may not need to take a trip to your local mechanic after all:

Air Filter: A clogged air filter won’t generate an error code, and can be easily replaced.

Fuel Pump: A fuel pump problem can be more difficult to diagnose and can be an expensive replacement part. Your car may not be starting properly if it is not trying to start and the gauge cluster does not show any warning lights. If this happens, your fuel pump may need replacing.

Tire Pressure: Low tire pressure (in and of itself) won’t cause your vehicle to run poorly, but it can cause added friction on the road surface. You might notice a difference in your vehicle’s driving dynamics.

Wrapping it Up

Modern vehicles are wonderful pieces of equipment, but they also wear out just like everything else we use on a daily basis.

You can detect serious problems early on by seeing the engine power light. When this light comes on, you should not wait to have it checked, especially if your vehicle goes into “limp mode” and performance is suffering.

Scan tools available at most shops and stores can give you a full read out of exactly what’s going on with your engine so that you can make the repair yourself or take it to a mechanic instead.

Whatever the issue may be, it’s good to know that your car has your back and has built in safeguards to help you and your family return home safely!

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