Most modern vehicles with an automatic (or even manual) gearbox go into limp mode when they detect a severe problem with the transmission or powertrain. Limp mode severely reduces engine power giving you just enough to slowly drive to a service station or prudently drive your vehicle onto a flatbed.
Your car won’t respond to the accelerator pedal. It won’t rev as hard and will not have enough power to accelerate to speed. You will get an ‘Engine Power is Reduced’ warning on the dashboard accompanied by the Check Engine Light in more elaborate cases.
Limited engine power mode (limp mode) is meant to protect your vehicle from further damage. Bypassing it isn’t wise. Do the necessary repairs, and your car will be back to normal.
Why Do Cars Go Into Reduced Engine Power?
The ECU forces your engine to produce way less power when it detects a severe malfunction to protect itself. Less energy means the transmission and the engine are working less complicated, giving them a chance to limp home or a service station without causing more damage.
The ECU can completely cut fuel and electronics to the engine rendering the vehicle inoperable in severe cases.
What Makes the Reduced Engine Power Warning to Pop Up?
Before thinking of how you can bypass your vehicle’s limp mode activation and get rid of the reduced engine power warning, you first have to find out some of the most common issues that can trigger the condition.
Different manufacturers program their vehicles to react differently to detected faults. This means a wide range of causes can trigger this mode, and only your user manual or a scan tool can help you pinpoint your specific problem.
The most common problems that will trigger a reduced engine power warning include:
A Problem With the Transmission
A faulty transmission is one of the most common causes of the Reduced Engine Power warning in automatic vehicles.
Anything ranging from overheating to low transmission fluid can trigger limp mode in some cars. The power control module constantly monitors how the transmission is working and will reduce power when it senses severe lags and problems with the gearbox.
A Clogged Catalytic Converter
While a clogged catalytic converter will throw its error code long before the vehicle goes into limp mode, you can have issues if your catalytic converter gets clogged.
This will create intense backpressure to the engine making it less efficient and triggering the problem. This will also happen if you have a clogged PDF.
Faulty Sensors
Since modern vehicles rely on sensors to control virtually everything in the car, you will have issues when one or more critical sensors can’t feed accurate information to the control modules.
While most sensor failures will go through specific errors, a combination of faults could trigger limp mode if the consequences are dire.
For instance, problems with your throttle in a drive-by-wire system and the brakes might limit power from the engine since it makes the vehicle very dangerous to drive. Other manufacturers won’t let this trigger ‘Power Reduced Mode’ since it doesn’t pose a straight risk to the engine or transmission.
A Faulty ECU
Your main ECU and power train control module are in charge of how much power the engine generates.
While they will limit power based on information from sensors across the vehicle, they can also do this if faulty. Reducing power could be a failsafe on a faulty ECU that can no longer operate within required safety parameters.
Limp mode is better than having a runaway car with a stuck throttle because of a short or malfunction in the ECU.
Aftermarket or Stock Anti Theft Feature
Limiting the amount of power your engine generates and gradually shutting it down is a great way to immobilize a vehicle.
Some aftermarket and stock safety features allow owners to remotely limit power – either moderately or severely – to control what another authorized or unauthorized driver can do with the vehicle.
For instance, limiting power in a Hellcat when you give it to the valet or your son could be a great way to keep them safe.
If you feel your vehicle has limited power and there’s no check engine light, there’s a possibility the limit is intentional.
Engine Operating Outside Set Parameters
Another possible cause for limp mode is if your engine is operating outside set parameters and you’ve made no effort to fix it.
Simple problems like low oil pressure, engine running lean, overheating and more can all culminate into limp mode.
The ECU will first throw specific error codes before escalating into reducing engine power if you keep on ignoring the MIL.
Get a Scan Tool and Read Error Codes
The surest way of telling why your Engine Power Limited light is on is by using a scan tool. The ECU has specific errors related to the limp mode already stored. All you have to do is pull them out to figure out what you have to fix in the vehicle.
Can I Bypass the Engine Power Limited Mode?
Bypassing limp mode is possible and complex. You have to trick your ECU into thinking everything is OK so that it can restore full engine power.
With modern cars being so intelligent and electrified, this is more trouble than it is worth. The best course of action would be figuring why the mode was activated in the first place and fixing that.
If it is due to an aftermarket or stock power limiting feature, then talk to the vehicle’s owner. They will have a key or a pin to deactivate the mode if they want. Bypassing power limiters, in this case, could be interpreted as vandalism because the owner set it up for a reason.
Sometimes, Reduced Engine Power mode could be due to faulty sensors or an error in the ECU. Restarting the vehicle could sort out the issue.
- Limp the car to a safe spot
- Turn everything off
- Wait for five minutes
- Turn it back on and let it idle for a minute to see if the message pops up again.
Even if you are lucky and the car doesn’t go back into limp mode, it is still wise to have it checked, and the error codes read to find out what caused limp mode.
Note: If the limp mode was due to an overheating transmission or rolling fault in the powertrain, it could go away and come back again as you start driving. Have the vehicle inspected
How Fast Does a Car Go in Limp Mode?
The top speed will drop drastically when your car is in reduced power mode. This could be anywhere between 30 and 45MPH, depending on the manufacturer. In some cases, the power reduction will keep creeping, reducing your top speed further.
Note that the speed will depend on where you are driving, your overall engine power, and what you are carrying. It is a power limit, not a speed limiter.
For instance, while the car could hit 40 MPH going downhill, it will struggle to hit 25 MPH going uphill. You will have more trouble if it’s fully loaded or you are towing.
What Should I Do If My Car Goes into Limp Mode
If you get the ‘Power Limited’ warning or your vehicle is in limp mode, and you don’t feel it as powerful as it should be, you should first check if the ‘Check Engine Light is on.
If the light is on, it means the ECU has detected a severe fault in the powertrain. You have a few options.
If you are a short distance (less than 5 miles) from any of the following, you can:
- Drive to a mechanic and have them inspect your vehicle
- Drive home and inspect your car (if you work on your cars or have someone who can check it from home)
If you are further off, you can:
- Call a mobile mechanic to assess the vehicle and advise if it can slow limp to the shop without further damage
- ORganize to have a tow truck or flatbed carry the car to a mechanic for servicing
While most people will limp their vehicles for miles to get help, it isn’t wise unless you have no option. The car limited your power to protect itself. You can protect it further by not driving it for 30 miles.
Furthermore, driving on public roads at 20 to 30 MPH is dangerous. You will be way slower than traffic making you a potential obstruction and hazard to everyone on the road.