Limp Mode, also called Fail Code condition, is an engine protective feature that shields your car engine from damage by switching off some of the features or functionalities of the vehicle. For example, you over-speed or push your vehicle too hard when accelerating and the engine sensor detects that you are pushing the engine to the limit. That's when limp mode sets in to protect your engine from damage. It immediately lights the check engine light indicator on the dashboard and lowers the engine power. We can take limp mode as a measure that activates to help you drive your car home or to a garage without any additional damage.
So what causes limp mode?
As mentioned, pushing the engine too hard causes limp mode. In older vehicles, it mainly results from transmission issues, since most of the sensors fitted to old car models are transmission sensors. However, with the advancement of technologies in new models, more and more sensors are being incorporated, such as sensors for braking, electrical and wiring, tyre pressure monitoring, engine oil, fuel, or charging for electric vehicles. All these sensors connect to the vehicle's computer system (ECU), and the majority of them can trigger limp mode, depending on the problems or issues they detect. Among the common causes of limp mode are:
- Pushing the engine too hard - over speeding or accelerating too hard typically causes limp mode.
- Malfunctioning of the sensors - sensors may also be faulty, sending the wrong information to the ECU, which may lead to activation of limp mode. Issues with the wiring that connects the sensor to the ECU may also cause the same behaviour.
- Errors in the vehicle’s computers - similar to other parts of a car, the vehicle-computer may also malfunction, giving wrong instructions to the systems relying on the computer. As a result, the ECU may wrongly activate the limp mode when the car has no issue at all.
- Braking problem - advanced vehicles have sensitive brake sensors that may send the car into limp mode if there is an issue with the brakes.
- Transmission troubles - the transmission system is one of the closely monitored parts in a vehicle, and any problem in it may automatically activate the limp mode.
- Detachment of cables going to the transmission - the sensor captures it as a malfunction.
- Turbo over-boosting – going overboard more than what your engine can handle may damage the piston and activate a limp mode.
- Modifications to the engine, transmission, or wiring among other sensor sensitive parts - the alteration may not be in tandem with the vehicle computer, confusing it to send the car into limp mode.
What happens when a vehicle is in limp mode?
Without proper diagnostic equipment, ascertaining that a car is in limp mode would be a challenge. Vehicles behave differently and show varying signs, including the following:
- The check engine indicator lamp on the dashboard turns on, although other engine problems not necessarily limp mode may also trigger this.
- The car lowers its engine power such that it cannot rev past 2000-3000RPM depending on the vehicle. Different engines reduce the engine power differently including, withdrawing the turbo boost, blocking the transmission from shifting into higher gears, and delaying the shifting of gears in automatic transmissions.
- After a long drive, the temperature continues reading cold or extremely high.
- Vehicles with combustion engines start emitting darker or more whitish or bluish smoke.
- Turbo produces odd sounds, perhaps due to its limitation.
Solutions to the Limp Mode Issue
Before even thinking of solving a limp mode, the first step should be to get a proper diagnostic to ascertain that your car is on limp mode. A car mechanic or service provider with a car diagnostic tool will quickly confirm the problem with your vehicle and provide you with a solution.
If your car went into limp mode after you've pushed it too hard, a simple stop and switching the engine off would restore the automotive into normal mode. Some vehicles may require you to disconnect the power source temporarily and let the engine completely cool down before restarting. On switching the engine back on, the car should start in its normal mode, but if it doesn’t, you should consult a technician.
For vehicles that don’t switch back to the normal mode, the first step in restoration should be identifying the cause of your car going into limp mode and rectifying the problem. It can be a transmission, engine, braking, or wiring problem. It can also stem from the sensor or the computer itself. Engaging a technician to identify and repair the problem is more advisable.
After identifying the cause, the next step should be clearing the error code from the vehicle computer. There are various ways to clear the code, depending on your car's make and model. Some may require resetting the modules and the sensors, and others may require bypassing the error or removing the error with a diagnostic tool. As a result, it is advisable to have an authorised technician clear the error for you.
Once the error has been cleared or bypassed and the modules and sensor reset, your vehicle should resume its optimal performance.
Yes, a limp mode can be a pain in the neck, but it serves the need. It saves you more than you can imagine since restoring a vehicle from limp mode is a small fraction of what you would spend in replacing a whole engine or other vehicle parts. At Carparts.com.au, we connect you with authorised car technicians, whether you need a simple car repair, resetting back from limp mode, or bypassing the error code. Learn more from our blog on how to keep your vehicle in top condition.