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 overspeed 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 turns on the Check Engine light indicator on the dashboard and lowers the engine power. So it’s a safety measure that is activated to help you drive your car home or to a garage without any major damage.
What Causes Limp Mode?
In older vehicles, limp mode 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 limp mode causes 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 the 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 - like 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 problems - 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 compatible 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 vary in the signs they show. Here are some limp mode ‘symptoms’ that you will notice:
- Check Engine light is on – This dashboard light turns on, although other engine problems other than limp mode may also trigger this.
- Low engine power – The car lowers its power and usually cannot rev past 2000-3000RPM (depending on the vehicle make/model). Different engines reduce the engine power in different ways. They can withdraw the turbo boost, block the transmission from shifting into higher gears, and delay the shifting of gears in automatic transmissions.
- Inaccurate temp reading – After a long drive, the temperature continues reading cold or extremely high.
- Unusual emission – Vehicles with combustion engines start emitting darker or more whitish or bluish smoke.
- Odd sounds – Turbo produces odd sounds, perhaps due to its limitation.
How to Bypass Limp Mode
Before even thinking of solving or bypassing limp mode, the first step should be to get a proper diagnostic to confirm limp mode in your car. An auto mechanic can quickly confirm the problem and provide you with a solution.
If your car went into limp mode after you've pushed it too hard, you can restore it to normal mode by stopping and switching the engine off.
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 should be identifying the cause of your car going into limp mode and resolving the issue.
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 recommended.
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. You will need a technician to 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, limp mode can be a pain in the neck, but remember that it is a protective feature in your car and not a defect. It is there to serve a purpose, and that is to save your car from a major damage by temporarily disabling some functions.