Whether you drive a Beemer, Toyota, Honda or any other make, your vehicle is engineered to protect itself from suffering catastrophic damage. This is essentially where the engine failsafe mode comes into play. Some people call it limp mode, and in other instances, it’s referred to as an engine cut off safety feature. Regardless of the name, understanding what an engine failsafe mode is, what to do when it happens, and how it’s fixed will help you prepare for this unfortunate and highly stressful situation.
Understanding the Engine Failsafe Mode
Modern cars, trucks and SUV’s are equipped with an OBD-II diagnostic system that monitors all vehicle systems including the:
- Ignition System
- Fuel System
- Emission System
- Drivetrain (including engine, transmission, axles)
- Braking System
- Vehicle Stability & Traction Control
- ...and much more
Using a series of sensors, the engine control unit (ECU) collects data instantly to ensure the vehicle operates as efficiently as possible. It also helps to make fine-tuning adjustments to these systems to keep the car, truck or SUV running safe and efficient. When one of these sensors detects a mechanical fault, usually in the engine or transmission of the vehicle, it will trigger an OBD-II trouble code that activates the engine failsafe mode.
What Happens When the Engine Failsafe Mode is Activated?
Once this failsafe or limp mode has been activated, the ECU will limit the vehicle’s ability to drive normally. In some instances, the ECU will permit you to drive home or to a mechanic but will restrict the performance or speed of the vehicle, so the damage will not get worse. This is where the term “Limp Mode” comes into play, by allowing the car to slowly get to a destination for diagnosis and repair.
There are some instances that will cause the failsafe mode to disable the vehicle’s ignition or fuel system. This will cause the engine to “fail” to start. This can be a blessing, especially if there is minor mechanical damage that can progressively get worse if the engine continues to run.
What Causes the Engine Failsafe Mode?
Sometimes the engine failsafe mode is triggered by an actually damaged component, such as an oil pump, timing chain or belt, crankshaft or camshaft, or other internal engine components. It’s also common for damaged transmission components like inner gaskets, seals, the torque converter, mechanical gears, the input shaft, or even a damaged flywheel or driveshaft to cause the failsafe mode to activate.
It's also quite common for a sensor failure, or a damaged electrical connection to a sensor, to “accidentally” activate this warning system. Professional mechanics will fully inspect the vehicle to locate the exact source of this problem before clearing the codes and testing the repairs.
How is the Engine Failsafe Mode Diagnosed?
Since this safety system is activated through the ECU or powertrain control module (PCM), with transmission-related issues, a professional mechanic will start by downloading the error codes stored in these computers to begin the diagnosis process. Sometimes the engine failsafe mode is triggered due to a sensor failure or an electrical glitch. It’s also common for a security system fault to engage this warning light, which means it’s not always a mechanical issue that’s causing the failsafe.
Some people believe it’s possible to reset the engine failsafe mode through some less-than-reliable methods. This is not true, nor is it effective at resolving the problem. A professional mechanic should always be contacted to complete an onsite inspection to correctly diagnose the root source of the engine failsafe mode. This will permit them to recommend the right repairs or reset the error if it was a minor glitch.