Driving along and suddenly noticing that you have reduced engine power isn’t a feeling anybody likes. At all.
Sometimes, it can be a dangerous situation. You have to watch what’s going on all around you and be very aware of staying out of the way of faster-moving traffic. Other times, it’s merely a nuisance.
Either way, reduced engine power isn’t something you want happening if it’s possible to avoid it. In this article, we’ll be looking at what causes reduced engine power and what you should do if it happens to you. As well as this, we’ll explore some potential solutions.
Manufacturers build some cars with reduced engine power warning lights or messages that pop up. These aren’t universal, though. Instead of this, you may see words closer to “limp mode”, “limp home mode“, or “safe mode” or the ever-worrying check engine light.
So, if one of those lights has popped up, or you can feel a reduction in engine power, or you just want to know what to do in case it happens, we hope this article contains your answer.
- Reduced Engine Power Meaning
- Limp Home Mode
- Common Electrical Causes
- Common Mechanical Causes
- Common Questions
- Check Engine Light Flashing – What’s Causing It?
- Service Engine Soon – What Does It Mean?
- Ignition Coil – How To Diagnose and Replacement Cost
What Does Reduced Engine Power Mean?
When I say “reduced engine power”, I refer to an engine that isn’t operating at peak efficiency. When your motor doesn’t have as much power as it usually does, it will be evident to you.
As the driver of your car, you’ll know it better than anyone else. If something’s wrong, you are the person who is most qualified to pick up on it. Therefore, if you feel like something’s wrong, something probably is. And, hey, it’s always better to be safe rather than sorry. Don’t be ashamed of taking your car to a mechanic for a check over.
Sometimes, a power reduction isn’t so apparent. You might not be so aware of it if you rarely accelerate hard or travel particularly quickly.
The best way to test out your suspicion is, quite simply, to put your foot down in a low gear. The car should throw itself forward, and you should feel the power roar from the engine, whether you’re driving with 60bhp or 1,000.
If this doesn’t happen, you have reduced engine power coming from your vehicle.
Of course, if the manufacturers fitted your car with a visual warning system for this, it will simply tell you. Many General Motors cars, such as Chevrolet, Cadillac, Buick, and GMC, are fitted with this light on the instrument cluster.
As well as this, the “Check Engine” light will also probably turn on.
What Are The Symptoms Reduced Engine Power?
If you have reduced engine power, you’ll notice the following:
- The car will feel sluggish – as in, not very responsive to your throttle inputs (pressing the gas pedal).
- It won’t accelerate very quickly, if at all.
- The top speed may be considerably lower than usual, with the engine unable to provide enough power to overcome the opposing forces at this point. When this happens, it’s referred to as “terminal velocity” – or, to most of us, just “top speed”.
You may also notice some of these symptoms, although it depends on the root cause of the problem.
- Shaking and vibrating coming from the engine block.
- Shaking and vibrating coming from the gear shifter, especially in a manual transmission.
- Warning lights could appear on the dashboard.
- You may find the car stalling when the engine idles.
What Causes Reduced Engine Power?
The potential causes of this are almost unlimited – far too many to type out in one article. I will attempt to go over the main ones and provide you with the necessary knowledge to diagnose the problem yourself.
To diagnose any issue with a car, you can often use an OBD II diagnostic tool. “OBD” is “on-board diagnostics”. Nowadays, cars are basically just advanced computers. Engineers code them to run programs that will highlight the specific problem in the car.
The OBD reader will either show an error code or detail the exact problem in English text.
This reader is handy for saving time. In many newer cars, the OBD reader can provide in-depth detail on the issue. For example, it might tell you that there is a misfire in cylinder 3.
I have divided some of the leading causes of reduced engine power into categories.
Limp Home Mode
Limp Home Mode – otherwise known as “limp mode” or “safe mode” – is present on most modern cars.
The car detects, through sensors, when a fault has developed somewhere in the powertrain – that is, the engine or transmission.
Once the car finds a problem, it activates Limp Home Mode. This is essentially a program that instructs the vehicle to run as gently as possible, putting minimal strain on the engine and transmission.
- Misfire, caused by a faulty…
- Spark plug
- Ignition coil
- Sensor issues
- Lambda (oxygen)
- Throttle position sensor (TPS)
- Mass air flow (MAF)
- Wiring and harnesses
- Throttle plate
- Fuel pump
- General engine issue
- General transmission issue
What Is Limp Home Mode?
You can find limp Home Mode on most relatively modern cars.
Nowadays, cars are more and more dependent on electronics, with mechanical aspects fading into the past. We use sensors instead of linkages, batteries instead of engines, and advanced ECUs instead of 3 basic fuses.
As part of this electronic reform, manufacturers introduced Limp Home Mode. Using the many sensors in the vehicle, it continually monitors everything. If a problem arises – for example, if one of the sensors detects a problem with the throttle position sensor, then the ECU will activate Limp Home Mode.
If you’re limited to one or two gears and about 30 to 45mph, you’re probably in Limp Home Mode. The car might even tell you directly.
When Limp Home Mode is activated, it slows everything down, reducing the engine’s power and the amount of work it does. The more you push your motor, the greater the risk of more damage. Limp Home Mode is a way of preventing this.
You shouldn’t use Limp Home Mode to cover very long distances. Try to drive in short bursts wherever possible.
It can be dangerous to drive with Limp Home Mode activated on fast roads where you might cause congestion or an accident. If your speed is severely limited, you should pull over and try restarting the engine. Unfortunately, if this doesn’t fix it, you might need to call for assistance.
How Do I Fix Limp Home Mode?
Interference with the “logic” of the ECU’s systems causes Limp Home Mode.
Usually, it’s a sensor issue.
For example, the sensor has picked up a reading. This reading is either consistently too high or too low compared to what it should be or is too high or low compared to another sensor reading.
The ECU activates Limp Home Mode as a result.
Causes of Limp Home Mode can be divided into three categories (in order of likelihood).
- The sensors pick up a genuine problem with the engine or transmission.
- The sensors themselves develop a problem and don’t read the environment accurately. These misreadings lead the ECU to think there’s a problem with the engine.
- A problem with the ECU – it’s possible for this to happen. I have seen it before. In this situation, the ECU needs to be reprogrammed. This is an expensive job but, unfortunately, unavoidable. You won’t be able to do this one at home. It’s that or scrapping the car.
For all of these, the first thing you’ll need to do is to plug in an OBD II code reader. It will tell you exactly where the problem lies so that you or a technician can address it efficiently.
You will need to either fix or replace the faulty part.
How Is Limp Home Mode Relevant To Reduced Engine Power?
If you drive a modern car, chances are it’ll have Limp Home Mode installed on it. When this is active, the ECU reduces engine and transmission activity as much as possible, causing reduced engine power.
Many of the issues we will touch on soon will cause Limp Home Mode to activate.
What Are Some Common Electrical Problems?
What Is A Misfire And How Do I Fix It?
A misfire happens when the spark plug doesn’t ignite the fuel/air mixture within the cylinder. When this happens, there will be no power stroke. No power stroke? No power.
Usually, a misfire only affects one or sometimes two cylinders. The result is an engine with reduced power but one that might still be able to run, albeit sluggishly.
If all the cylinders were misfiring, the engine wouldn’t continue to run.
A misfire results in reduced engine power, something you’ll be very aware of when driving.
Open the hood and see how much the engine is vibrating and shaking. In a manual transmission, you’ll also feel this through the gear shifter.
You could also plug in an OBD II code reader. It may even tell you the specific cylinder that needs attention.
The fault usually lies with the spark plug but could be due to a faulty ignition coil. It’s worth using a multimeter to test each spark plug and each ignition coil. Alternatively, you could just replace the lot. In some cars, this is an affordable process. In others, not so much, and you want to make sure you’re replacing the correct component.
What Sensor Issues Cause Reduced Engine Power?
The newer your car is, the more sensors it’s likely to have. Any of the hundreds (literally!) of sensors in a new vehicle could lead to Limp Home Mode activating.
To diagnose a problem with any of these, it’s wise to use an OBD II code reader. It’ll save you an awful lot of time.
We will briefly consider three of the most infamous ones.
Lambda Sensor/Oxygen Sensor
The lambda sensor is another name for the oxygen sensor.
It was named “lambda” because engineers used this Greek letter to describe the sensor’s voltage range. It compares the level of oxygen in the exhaust to the amount in the atmosphere.
These readings give feedback to the ECU. As a result, the amount of oxygen going into the chamber can be increased or reduced. This leads to efficient, eco-friendly combustion.
A fault with the lambda sensor may cause the engine to run “rich” or “lean” – that is, too much fuel per unit of air or not enough. It could also trigger Limp Home Mode.
Old cars have one of these sensors. Newer cars have two. You’ll usually find the first on the exhaust manifold and the second partway down the exhaust pipe underneath the car.
In almost every case, a simple replacement is the best way forward. Remove the old sensor and install the new one.
TPS – Throttle Position Sensor
In newer cars (again), manufacturers use throttle position sensors in place of mechanical wires. Rather than a physical connection between the pedal and the throttle plate, a sensor is used. This sensor is the TPS – the throttle position sensor.
You can find the throttle plate within the throttle body.
If a fault develops with the TPS, the ECU will not accurately convert the pedal’s input into greater or reduced engine power. Since the ECU will be unaware of your exact inputs, it would activate limp Home Mode to reduce the risk of accidents.
MAF – Mass Air Flow Sensor
The MAF sensor records the mass of air entering the engine. You can find it between the air filter and the intake manifold. You can see it clearly whenever you open your car’s hood.
When this sensor develops a problem, it means the ECU isn’t aware of the exact amount of air entering the engine. As a result, the ratio of fuel entering the engine is also wrong. Again, you’ll end up with an engine either running too rich or too lean.
Faults with the MAF sensor don’t usually directly lead to Limp Home Mode. However, stalling, reduced engine power, and cranking but not starting are all symptoms that something has gone wrong with it. Extended problems could include transmission shifting patterns changing.
Changing the MAF sensor might be slightly trickier than some other sensors. You may need a basic knowledge of rewiring. It might be possible to carefully clean it, although be careful – you’re working with electrical equipment.
What Other Electrical Issues Cause Reduced Engine Power?
ECU – Engine Control Unit
The ECU functions as your car’s central computer system. It considers readings from every sensor in the vehicle. It continually adjusts things such as fuel delivery to maximize engine performance.
Older cars have far less advanced ECUs. If you go back far enough, there’s no ECU at all. Automotive manufacturers first used it in 1970.
In modern cars, there are hundreds of small ECUs, each managing a different aspect of the vehicle. When we use the term “ECU”, we are referring to the whole system.
ECUs can develop faults. It’s relatively rare but certainly possible. These faults could be due to trauma of some kind or a manufactural defect.
If a fault develops with the ECU, you might notice many things start to play up. Everything from your windshield wipers to your lights might act a little strange.
Limp Home Mode may come on as a result of this. The ECU can’t make sense of the readings it’s receiving and thus assumes a worst-case scenario.
I once had a customer come in for a new wiper motor – theirs wasn’t working correctly – and the root cause turned out to be a faulty ECU. It needed reprogramming by an automotive electrical specialist.
This is, unfortunately, an unavoidable and high cost if you want to keep the car.
If this is the problem, you’ll almost certainly need an automotive electrician. If you know your way around electrical components, you may be at an advantage here.
There can easily be well over a mile of wiring in a new car. In technical terms, that’s absolutely loads. A fault with your wiring system could be anywhere in here.
Faulty wiring harnesses could cause reduced engine power in the same way that faulty sensors might.
What Are Some Common Mechanical Problems?
If your engine power is less than usual, the problem could be mechanical.
In my experience, the newer your car is, the greater the probability of the cause being electrical. The reverse is also true: mechanical problems are usually at fault in older vehicles with reduced engine power.
Here are four things you may want to consider.
The throttle body, as mentioned earlier in this article, contains the throttle plate.
Traditionally, the plate was connected to the throttle pedal via a wire. As you push the pedal down, the plate rotates and allows more air past it and into the engine. In newer cars, this is done electronically using a throttle position sensor.
You can think of this process as similar to the bellows used to increase a fire’s heat. More oxygen = more heat and power. The same process is what happens in an engine.
As well as the throttle position sensor not working, the throttle plate can sometimes become stiff or dirty.
One of the main symptoms of this fault is the car having reduced engine power and, in particular, struggling to maintain its idle. It may stall unless you have your foot on the throttle pedal, keeping the revs up. You may also notice that it takes longer or shorter than usual for the revs to reduce when you blip the gas.
Before doing anything else, you can try cleaning it out and lubricating the plate’s hinges. Remove the air intake and the sensors and then the throttle body.
With parts cleaner, spray the plate down and wipe it with a cloth. Don’t worry; it won’t break – although it’s best to be sensible. Lubricate the hinges with a bit of WD40 and open and close the plate using your hands to work it in.
Reinstall everything and see if that fixes the problem. I had this issue once, and this method solved it for me.
If that doesn’t work, you may have to try getting a new throttle plate or body.
Any fault with the fuel pump could lead to too much or too little fuel going to the engine. In extremes, both of these can result in reduced engine power, either directly or by causing the ECU to turn on Limp Home Mode.
If this is the problem, an OBD II reader may or may not pick up on it. You might need a specialist diagnosis.
Remember, you’re working next to gasoline. It’s an easily combustible fuel, so be extremely careful.
If you’re in any doubt at all, get a professional mechanic to do this job for you.
Replacing the fuel pump often also needs an ECU recalibration, as the car may not recognize the new one correctly.
Overall, although it’s possible to diagnose and fix this one yourself, we’d recommend getting it done professionally, if possible. Many important things could go wrong and be damaging to both you and the car.
General Engine Issue
Okay, this may sound like cheating, but hear me out.
There are so many possibilities when we think about what could go wrong in an engine – almost limitless different combinations.
Therefore, I’ve included this section on “general engine issues”.
If there’s any sort of problem with your engine, at all – whether it be sensors, crankshaft, camshaft, fuel, air, timing chain, con-rods, gaskets, piston rings, seals, coolant, lubricant, etc. (the list goes on) – you could see reduced engine power.
As with other things on this list, this could be the direct cause, or it could trigger Limp Home Mode.
If you’re unsure, it might be time to take the car to your local auto shop.
General Transmission Issue
Again, this might be somewhat like cheating, but there are so many possible things that might go wrong in your transmission.
With your transmission not working correctly, it could result in the feeling of reduced engine power.
If a sensor in the transmission detects a problem, the ECU may activate Limp Home Mode.
Another possibility is that the engine’s output is actually fine, and the problem lies with the transmission. To check this, you could put the car in neutral and see how the engine reacts to your throttle movements. Keep the parking brake on and only do this in a safe environment, such as on your driveway.
Transmission problems will need to be looked at by a professional.
Common Engine Power Questions
How Can I Prevent Reduced Engine Power?
Looking after your car is the first thing you should be doing. The more you take care of it, the healthier it will be.
Performing routine maintenance on things like checking the oil and coolant levels and changing filters will help the engine last longer. Use good quality fuel and make sure you don’t over- or under-run the car, as both of these will reduce an engine’s working lifespan. Finally, when problems do arise, always get them fixed as soon as possible. This will always be the best and cheapest option.
Could Turbo Lag Be The Cause Of Reduced Engine Power?
Sometimes, cars come with big turbos. This is especially true of cars built in the 80s and 90s.
These big turbos can take a while to spool up, so they may feel extraordinarily slow for the first few moments after you put your foot down. After that, though, provided the turbocharger is working, the boost should kick in.
This period of delay before the extra power is known as turbo lag.
If you’ve bought a second-hand car with a large turbo, this may be what’s happening. Don’t worry, there’s nothing wrong with the car, and you’ll soon get used to it.
Some people like to retro-fit another, smaller turbo. With two turbos, one big and one small, you have an efficient bi-turbo system. This bi-turbo system eliminates most turbo lag. It’s not necessary, though, and quite expensive. All modifying always comes with some risk.
Of course, if there are lights illuminated on the dashboard, it’s another story entirely. Follow some of the ideas listed above, and hopefully, you’ll find your answer.
What Should I Do If My Engine Power Reduces While Driving?
If your engine power reduces while driving, you may be able to continue, especially the case if you aren’t on a busy road or putting yourself or others in danger.
I wouldn’t recommend continuing if the car is struggling to get up hills or if you notice any strange smells or noises. Also, if the car tells you to stop, stop.
On a freeway, it may be too dangerous to continue. You must be your own judge in this situation. If at all unsure, it’s best to pull over and wait for a less busy time to drive. Put your hazard warning lights on.
Remember: Limp Home Mode is designed to do just that – to get you (and your car) home, slowly and safely.
In all of these situations, get your car to a mechanic as soon as possible. Alternatively, try fixing it yourself.
Why Is My Engine Stalling?
Aside from the typical situations (such as not being gentle enough with the clutch), stalling at idle usually indicates a problem with the engine’s oxygen flow.
You should check all the components of this system and hopefully will find the answer somewhere in there.
- the throttle body
- the air intake pipes
- the air filters
Clean as much of it as you can. That, hopefully, should fix the problem.
If the engine stalls while running (not a pleasant situation to be in!), then there’s a much more severe issue at play. Get your car towed to the shop and be prepared for it to be there for a few days.
Is Reduced Engine Power Dangerous?
The answer to this question is that it depends on the situation. However, yes, it certainly can be.
Although “POWERRR” is something you might associate with Jeremy Clarkson’s lead foot, it’s not solely useful in racing situations. Sometimes it’s necessary to accelerate hard to avoid accidents or other incidents. You might also need to travel quickly (within the speed limits).
If your engine power is lower than it should be, you wouldn’t be able to do these things.
If you notice that your engine’s power level has dramatically reduced, don’t wait to get it fixed. Do it as soon as possible.
What Is The Reduced Engine Power Message?
You’re most likely to see this message on a GM car.
Check out this video for an interesting example.
Can I Fix Reduced Engine Power Myself?
In conclusion, yes, for most things. But, it’s important to note, a whole range of things can cause reduced engine power. Don’t be embarrassed if you need some help in the end.
In most cases where you find yourself low on power, the answer will be a simple one. Unfortunately, sometimes it’s a complex and expensive one, and there might be no way to avoid either a hefty cost or having to write the car off.
The main lesson to take away? Reduced engine power, and Limp Home Mode, aren’t just irritating nuisances. They need to be dealt with as soon as possible to avoid any further damage.
Hopefully, you can find the answer to your problem in this article. Either way, please feel free to leave a comment below.
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