Car Repair and Maintenance

How to Fix Reduced Engine Power [Complete Guide]

You want to fix reduced engine power if you suddenly notice significant loss of power in your car. Usually, the lights will flash on your instrument cluster, and when you press down on the throttle pedal, nothing happens. Reduced engine power is the last thing you want to happen to you while driving as it hinders your driving experience. This problem is fixable, especially if you have the expertise and tools.

How to fix reduced engine power

How to fix reduced engine power

As mentioned earlier, this is a project you can DIY but if you don’t have the experience and tools, it’s recommended to contact a professional. Below are the steps to fix reduced engine power.

1. Gather the necessary tools

The things needed are:

  • A tool kit
  • A multimeter
  • An OBD2 scanner

You also need to have some expertise (but you can call the experts if you’re no good at DIYs).

2. Find out what the problem is

The first step to finding out why you are having reduced engine power is to scan your vehicle with an OBD2 scanner. You can easily buy this at any online store.

Steps to use the OBD2 scanner:

  • Plug the connector into the port in your car, this port is usually located under the driver’s side dashboard (or check your vehicle manual for the location).
  • Follow the OBD2 scanner instructions on how to diagnose and retrieve the problem codes.

In case you don’t have access to an OBD2 scanner, you can try any of the solutions below until you’re able to fix the “reduced engine power” problem.

3. Fix loose wire, clamp or harness

With your car properly parked, engine turned off, cooled down, and battery terminals disconnected. Look into your engine bay and thoroughly check for any loose, exposed or damaged wiring, clamp or harness.

Reconnect and properly tighten anything that’s loose or out of place, and make sure any exposed or damaged wiring is replaced with a like for like replacement.

4. Mass air flow sensor failure

With your car properly parked, engine turned off, cooled down, hood open and battery terminals disconnected, look for the mass air flow sensor.

This is usually located behind the air-filter box. Pull off the connector and use a screwdriver to remove the sensor.

Use a mass air flow sensor cleaner to spray the hole at the bottom of the sensor and let it dry for about 20 minutes before putting it back in place.

If this doesn’t solve the problem, then you need to replace your mass air flow sensor with a new one.

5. Oxygen sensor problem

These sensors measure and adjust the air-fuel mixture for proper combustion in the engine. A faulty or damaged sensor will cause the “check engine” or “reduced engine power” light to come on.

Most cars have more than one oxygen sensor in various locations, but typically there is one located by the catalytic converter and another in the hood near the motor.

With the car properly parked and cooled down, open the hood and look for your oxygen sensors, remove and clean them, then put them back.

If this doesn’t solve the problem or oxygen sensor codes keep returning, then you need to replace your oxygen sensor with a new one – Replacement oxygen sensors aren’t too pricey, but they don’t come cheap also. So you need to be absolutely sure before you begin splurging on a new one.

6. Clean the throttle body

With your car properly parked, engine turned off, cooled down, hood open and battery terminals disconnected, look for your car’s throttle body (usually located between the intake manifold and air cleaner).

Take out the air duct connector, clean with a throttle body cleaner (scrub gently with a toothbrush), and put it back. Start the vehicle and let it idle for some minutes.

If this doesn’t solve the problem, then you might need to replace the entire throttle body. It’s inexpensive and relatively straightforward to fix.

7. Change your air filter

Locate your air filter box (usually black) next to the engine, remove the filter box cover and take out the old air filter, put in the new one properly, then screw the air filter box cover back in place.

Replacing an air filter is a cheap and painless experience, even experts recommend replacing it every 20,000-30,000 miles. DRiV Automotive Inc., for instance, suggests 12,000 to 15,000 miles.

8. Check the distributor for any damage

With your car turned off and fully cooled, open the hood to locate the distributor, which is a silver colored cylinder shaped component near the engine.

Remove the distributor cap to inspect for any damage to the rotor, any visible damage such as rust or crack equals a new distributor.

To know the best way to do this, I recommend having your car owner’s manual handy when you want to do this.

9. Fix transmission problems

A transmission problem will most likely trigger a check engine light long before a reduced engine power problem occurs.

Although a scan is the best way to diagnose and fix problems with your transmission, most times a change of fluid or low transmission fluid may be all you need to fix this problem.

To check or replace your transmission fluid, you need to refer to your owner’s manual. But most times if the transmission fluid is black or deep brown with any visible signs of contamination, then it’s time to change the fluid.

If the fluid is low but clean or fairly transparent red, then you simply need to top it off.

10. Low engine oil

Low engine oil will definitely trigger a myriad of problems in your car

With your car properly parked, engine turned off, cooled down, open the hood and look for the oil dipstick.

If the oil is deep brown or black, then it has run its course and needs to be changed. If the oil is clean and close to the minimum level line then you need to add more oil.

Use only manufacturer recommended engine oil, and change it every 7,500 miles. Per Capital One, modern cars can manage 5,000 to 7,500 miles between oil changes. However, for cars that use a blended or full synthetic oil, 10,000 miles should be your limit.

11. Bad spark plugs

Bad spark plugs can lead to lethargic acceleration and engine misfires.

Changing spark plugs is quick, simple and cheap to do. Consulting your vehicle owner’s manual will guide you on how to do this.

Caution: Make sure your vehicle is turned off, properly cooled down and your battery terminals are disconnected before attempting this to avoid any injuries as spark plugs can get really hot after use.

12. Check your battery terminals for corrosion

With your car properly parked, engine turned off, cooled down, hood open and battery terminals disconnected, remove the battery.

Inspect for any white corrosion on the top of the battery terminals, if there is any; then simply mix a tablespoon of baking soda with equal parts water and use a toothbrush dipped into the mixture to scrub away the corrosion.

Use a damp towel to clean it off afterwards and put it back in your vehicle with the terminals reattached properly.

Tip: Experts recommend changing a car’s battery every three years, so if your battery is over 3 years old, then it’s advisable to replace it.

13. Clogged up catalytic converter

The catalytic converter is located underneath your vehicle; after the exhaust manifold. With the vehicle turned off, engine and exhaust entirely cooled down, jack up the car and use the proper tools to remove the catalytic converter.

Take it out and inspect it for any types of blockages or unusual substances like water, oil, soot and more inside it. If it is clogged up then you need to replace the catalytic converter.

Although this might seem like an easy fix, a catalytic converter replacement is a pricey fix. So I recommend having a mechanic do this in order to avoid any complications further down the road.

14. Malfunctioning ECU

Like the human brain, the ECU (Engine Control Unit) is the vehicle’s brain. It is the computer that controls every component of your vehicle and how they communicate with each other in order to perform optimally.

The only way to tell if an ECU is malfunctioning is by running a scan with an OBD2 scanner (by a professional mechanic).

Replacing an ECU doesn’t come cheap, so it’s best to leave this to the professionals.

What is reduced engine power?

Reduced engine power is simply part of a vehicle’s “limp mode”.

The “limp home mode” or “limp mode” is simply a power mode a vehicle’s computer defaults to when it notices a problem in any of the vehicle’s vital components in order to protect the other parts of the engine from serious and potentially expensive damage.

This is usually indicated on modern vehicles with a warning light on the instrument cluster.

What is reduced engine power light?

Although not found in all vehicles, this is a warning light similar to the “check engine light” that turns “on” on the instrument cluster when the vehicle’s computer detects a fault in any of the vehicle components necessary for the optimal performance of your vehicle (oxygen sensors, throttle body, fuel delivery systems and the likes).

Some vehicles don’t have this warning light or use it to indicate an engine problem, instead they simply default into “limp mode” or “reduced power mode”.

Causes of reduced engine power

  • Loose wire, clamp or harness
  • Mass airflow sensor failure
  • Oxygen sensor failure
  • Throttle body problem
  • Bad air filter
  • Faulty throttle position sensor
  • Transmission problems
  • Malfunctioning ECU
  • Clogged up catalytic converter
  • Battery problem
  • Low engine oil
  • Bad spark plugs
  • Engine misfire

While this list doesn’t cover all the causes of reduced engine power, it should give you an idea of some underlying issues that can trigger the “reduced engine power” warning light to come on.

Symptoms of reduced engine power

Here are a noticeable few symptoms of reduced engine power:

  • A myriad of warning lights on your instrument cluster
  • Lethargic acceleration
  • Inability to rev the engine past a certain RPM
  • Significantly reduced top-speed
  • Vehicle is unable to move at all

What should I do if the reduced engine power light comes on?

The first thing to do if you’re driving and the reduced engine power light comes on is to drive into the nearest repair shop for diagnosis immediately (if your home is quite a distance from where the problem occured).

Afterwards, scan the vehicle using an OBD2 scan tool to diagnose any faults and retrieve the problem codes.

Then fix or replace the faulty parts (as needed).

What if my car doesn’t have a reduced engine power light?

If your car doesn’t have a reduced engine power warning light, and you feel a sudden loss of power or the vehicle goes into “limp mode”, the first thing to do is to stop driving the vehicle.

This is done to keep the problem to a minimal level and not cause damage to other critical and expensive parts.

Then you can check any of the following components to know what the problem is and fix it:

a. Air filter

A clogged or bad air filter won’t throw a warning light, but it’s an easy fix.

b. Low tire pressure

Although this won’t throw up any error codes or serious performance issues, low tire pressure will cause added friction to the road surface, thus changing the driving dynamics of your car noticeably.

c. Fuel pump

On older vehicles faulty or malfunctioning fuel pumps won’t throw up any warning lights, however they might cause a noticeable drop in performance as a result of your engine running too lean.

Frequently asked questions

What causes reduced engine power?

Reduced engine power can be caused by one or a combination of issues such as loose wire, clamp or harness, mass airflow sensor failure, throttle body problem, bad air filter, faulty ECU, low engine oil, bad spark plugs and more.

Can I drive with engine power reduced?

It’s not recommended to drive with engine power reduced. This is because in some instances, the reasons for this problem might be minor while at other times they might be severe and potentially dangerous. So the best thing is to drive into the nearest shop to get your vehicle fixed.


Reduced engine power can be caused by anything as simple as a loose wire to something as serious as a faulty ECU and more.

The best thing to do when you notice it is to simply stop driving the vehicle to avoid causing any potentially expensive damages to other vital parts.

Although some of these fixes are fairly easy, it’s best to leave them to the professionals if you’re not handy with DIYs.

When it comes to fixing these problem(s), price isn’t the only consideration, quality is of the utmost importance, reliability and level of expertise of the ‘hands’ working on your vehicle is another important factor.

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Bernard Juchli

Bernard Juchli is an experienced racer, mechanic and team owner who trusts Avon Tyres.Bernard is the lead driver and force behind his Big Dog Garage Race Team. He is the General Manager and Chief Mechanic of Jay Leno’s Garage. Bernard and his crew of seven are responsible for all repairs, restoration and fabrication of Jay’s incredible automobile and motorcycle collection.

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