Reduced Engine Power – Limp Mode – What Does It Mean – Causes

Reduced Engine Power On Dashboard
Reduced Engine Power On Dashboard

First of all, This function can have many names depending on the year, make and model of your vehicle.

Whether its, reduced engine power, limp mode, fail safe mode or limp home mode, they all have the same goal.

Reduced engine power is the most common name for late model vehicles.

Your vehicle can have a wide array of control modules that monitor values from different sensors and actuators.

As long as these values are what it would normally expect, then it would perform normally.

However, if the control module all of a sudden receives unbalanced signals from one of the sensors that is out of the normal range (not within the parameters expected from this sensor), the computer is programmed to take some type of action.

So, depending on how far out of range this signal is, dictates what action will be taken. It may turn on something as simple as a check engine light (CEL). But, in some cases, may save diagnostic trouble codes (DTC)s, which will indicate where the fault occurred.

Consequently, anything that upsets the balance could cause a fault, and make any number of your error lights come on. But, when the computer detects a fault that is too far out of range, it will trigger this secondary mode.

Reduced Engine Power Mode Shown On Dashboard
Reduced Engine Power Mode Shown On Dashboard

As a result, you may see any one of the following:

  • Reduced engine power mode
  • Limp mode
  • Fail safe mode
  • Limp home mode

Just like when your home computer when it goes into safe mode, limiting functions that may cause further damage.  When your vehicle goes into this mode, it operates with limited functionality and speed. Finally, this mode is intended to help the driver get to a service shop safely.

Automotive Sensors
Automotive Sensors

As when the system detects a serious problem with:

  • Sensors
  • Circuits
  • Engine controls
  • Transmission components
  • Emission controls
  • Brake controls

The first three things to check will get you most of the information you need to solve reduced engine power issues:

Faulty Ground Connections ( Very Common )

Faulty engine grounds are sometimes to blame for many apparently faulty parts or wires. So one of the first checks you want to make is the condition of engine grounds, including battery connections.

A faulty ground connection will cause voltage, and current, to drop, leading to all kinds of driveability issues. So check the engine grounds in your vehicle with the use of a digital multimeter. This will make it easier to detect loose, corroded or damaged connections. As a result, affecting sensors, actuators or system circuits.

Diagnostic Trouble Codes (DTC)s

The first thing to check is the diagnostic trouble codes (DTC)s. You can use a scan tool to download trouble codes stored in the electronic control module (ECM) of your vehicle. Most of the time these codes will steer you in the right direction to see where the faults are.

Check For Technical Service Bulletins (TSB)s And Software Updates

Copy Of A Technical Service Bulletin (TSB)
Copy Of A Technical Service Bulletin (TSB)

Actually there are more issues than you think on this subject. Sometimes people jump into a repair without reading all of the appropriate service information. So, one way to stay informed is through the use of technical service bulletins (TSB)s. A (TSB) provides information on potential vehicle-related issues.

Hence, a (TSB) is a communication to update automaker publications, describe parts updates, inform of potential defects or failures, or relay enhanced or new service procedures. A (TSB) is not a recall, but rather an informative document alerting the public to a potential problem.

Common Causes To Come On Include:

  • A loose wire, harness, or clamp
  • Oxygen sensors are failing
  • Throttle position sensor is faulty
  • A throttle body issue
  • Mass airflow sensor is faulty
  • The vehicle’s (ECU) is faulty
  • Fuel pump issues
  • The catalytic converter is clogged
  • Fault in the transmission
  • Accelerator pedal position sensor
  • Bad ground

After scanning your vehicle, it should be fairly easy to pinpoint exactly where the issue is coming from.

Reading Engine Trouble Codes
Reading Engine Trouble Codes

Conclusion

Many of the causes of reduced engine power are issues that will need to be addressed immediately. However, this shouldn’t be a cause for panic. Consequently, most of these issues can be repaired with a little research and some basic know-how.

Taking your vehicle to a mechanic will cost a little more than making the repair yourself.  But, the benefit of their advanced scan tools will save you time and prevent any mistakes you might make.

Just remember the basics. Is a wire loose? Did a vacuum line fall off ? Do not look for a complicated solution to a simple problem. It is common to have a problem in one area that impacts three or four others.

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