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Can a Bad Battery Make the Reduced Engine Power Light Turn On?

Car battery

Of all the lights on a typical car or truck’s dashboard, the last one you want to see lit is the “reduced engine power” warning light. One big reason is that the light doesn’t denote problems most vehicle owners can easily fix themselves. That means you’ll need to make a trip to your local repair shop.

Even worse, if the light is triggered, it could shut down certain accessories, limit the speed you can travel and, in some cases, shut down your vehicle entirely. Many drivers have a question about this anxiety-producing warning light: can a bad battery cause it to turn on?

The answer, in most cases, is that a dead or damaged battery won’t cause the reduced engine power light to come on.  A battery with a loose ground won’t cause the light to turn on either. In short, the battery isn’t the problem if the reduced engine power light has come on in your vehicle.

Knowing that a bad battery won’t affect the reduced engine power light, you probably wonder what will (and what can be done to make the light turn off again). To find out, we performed the research for you and have the answers below. If your reduced power light is on, or you’re worried about what it means when it does, read on!

car and road divider

What Triggers the Reduced Engine Power Light?

Not all vehicles have a reduced engine power light, but in those that do, it’s tied into their vehicle’s onboard computer. When the computer senses a problem in any of the systems necessary for the vehicle to operate optimally, on it goes (and up goes your blood pressure). What are the problems that can trigger the light?

Your Vehicle’s Transmission Has a Problem

Although it will likely trip the “check engine” light first, a transmission problem can also cause the reduced engine power light to go on. Low transmission fluid might be the problem or possibly a slipping clutch.

There’s a Failing Oxygen Sensor

Your vehicle’s engine needs sufficient oxygen to work properly. The oxygen sensor measures the amount of oxygen entering the engine. If an oxygen sensor fails (or is faulty), the reduced engine power light will turn on until its replaced.

The Mass Airflow Sensor Has Failed

Like an oxygen sensor, the mass airflow sensor measures air density and pressure. It then relays the information to the onboard computer so the engine can mix the fuel and oxygen in the correct ratio. The reduced engine power light will tell you if this sensor fails or is faulty.

There’s an Issue With the Throttle Position Sensor or Throttle Body

The throttle position sensor tells the computer how much to open the throttle body when you step on the gas pedal. It also helps the transmission to shift when air enters the engine. The throttle body has a butterfly valve that, if clogged, can cause the onboard computer to think there’s insufficient air going into the engine. The reduced engine power light will light up if either has an issue.

close up of old throttle body of car in engine room
Image Credit: NONGASIMO, Shutterstock

Your Car’s Catalytic Converter Might be Clogged

Catalytic converters convert harmful carbon monoxide into less harmful carbon dioxide. Your vehicle’s reduced engine power light will turn on if it gets clogged. It will also light up if the converter has failed.

Your Vehicle’s ECU Has Failed

All of the sensors in your vehicle are controlled by the Engine Control Unit or ECU. In some cars, it controls practically everything. That’s not good because it’s one of the costliest parts to replace when the ECU fails. That’s why so many drivers fear the reduced engine power light because it can mean an expensive repair of the ECU.

car and road divider

What Happens if you Drive With the Reduced Engine Power Light On?

The answer to this question depends on the problem causing the light to come on in the first place. In most cases, you can safely drive with the reduced engine power light on because most of the issues that cause it to light up are minor. On the other hand, the light can go on when something much more serious is happening (as we discussed above).

Your best bet if the reduced engine power light comes on is to make sure it’s nothing severe, like an engine fire. If it’s not, your next step should be to take your car to an auto repair shop and have a certified mechanic check it out and determine the cause.

Can You Fix the Reduced Power Light Yourself?

Although the problem might be serious, if your vehicle’s reduced engine power light suddenly comes on, there are a few things you might be able to do to remedy the problem. Let’s take a look at them based on the issue that might be causing the light to engage.

Your Vehicle’s Transmission Has a Problem

If the transmission fluid is causing the reduced engine power light to turn on, you can quickly check the fluid and add some if necessary. You can also drain and replace the transmission fluid, but if adding some doesn’t solve your problem, replacing it will have little effect.

There’s a Failing Oxygen Sensor

If you can reach it, you might be able to clean the oxygen sensor. Be aware that, on most vehicles today, there are two of them. If cleaning the oxygen sensor doesn’t work, it will likely need to be replaced. If that’s the case, be aware that removing an oxygen sensor demands a special tool you’ll need to purchase. You can’t do it without the tool, but you can buy it easily.

The Mass Airflow Sensor Has Failed

If you have decent DIY auto repair skills, replacing a mass airflow sensor should be possible. There are many schematics, charts, and video tutorials that can be very helpful when you do.

car mass air flow sensor in the engine room
Image Credit: Nor Gal, Shutterstock

There’s an Issue with the Throttle Position Sensor or Throttle Body

Cleaning the throttle body is sometimes possible if it has become clogged with soot and dirt. Replacing it, however, will likely require the skills of a qualified mechanic. If the sensor is the problem, replacing the entire assembly might be less expensive.

Your Car’s Catalytic Converter Might be Clogged

While a skilled DIYer can replace a catalytic converter (albeit with a jack stand), the cost, around $2,000, can be prohibitive. It’s better to make 100% sure the converter is the problem before spending the big bucks on getting and installing a new one.

Your Vehicle’s ECU Has Failed

The only way to know if your vehicle’s ECU is the problem causing the reduced engine power light to engage is to have it checked by a mechanic. If it is the problem, you will likely need the same mechanic to replace it as the work demands specific computer and tuning skills.

Is it Safe to Drive with the Reduced Engine Power Light On?

As we’ve seen, several problems with your vehicle can cause the reduced engine power light to turn on. In some cases (but not many), the reduced engine power light will cause your car to shut down completely. If it doesn’t, and you’re sure that a deadly serious problem like an engine fire isn’t the cause, driving your vehicle should be safe.

It’s suggested, however, that you take your vehicle to a repair shop as soon as possible to make sure the problem is fixed before it causes even more significant (and more expensive) problems.

How Much does it Cost to Fix Reduced Engine Power?

If you’ve read everything up to this point, you know that several problems can cause the reduced engine power light to engage. You can fix some of those problems by cleaning a specific part, like a dirty oxygen sensor. If the ECU is the problem, the cost could be $2,000 or more, depending on your car or truck. That’s a huge difference and one that you’ll most likely need to figure out on your own or with the help of your local car mechanic.

car and road divider

Final Thoughts

Seeing your reduced engine power light come on, if you’re like most car owners, gives you that sinking feeling in the pit of your stomach. As we’ve seen, a bad battery can’t make this dreaded light turn on. That’s the good news. The bad news is that several problems that can cause the reduced engine power light to engage are very costly to fix. There’s some more good news, however, as there are a few problems you can fix yourself if you have decent automotive skills.

We hope the information, data, and solutions we’ve presented today have been helpful and will allow you to figure out why your reduced engine power light is burning (and causing you heartburn). If you take anything away from today’s article, it’s that, in most cases, the dreaded reduced engine power light doesn’t automatically mean big repair bills are in your future.


Featured Image Credit: 13_Phunkod, Shutterstock

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