We are occasionally asked if our products will remove power to the fuel pump in the event of a crash. The answer is complex, since it can change with how our products are connected to the TIPM (fuse box) and the type/severity of the crash, but we will answer this question below. Our engineers have researched how a TIPM might respond to such events, despite the difficulty in obtaining accurate wiring diagrams, firmware, and test data.
Keep in mind the fuel pump relay that is currently installed in your vehicle is capable of becoming stuck in the on position if it's faulty, which keeps the fuel pump running when your vehicle is on, off, or in a crash (approximately 20-25% of our customers have this type of fuel pump relay failure when they call us).
Types of Crashes
If you are involved in a low speed crash, many vehicles do not automatically turn off the engine and, subsequently, power to the fuel pump (by design). By disabling the vehicle, the driver could be placed in more harm with the inability to control steering, brakes, and acceleration - especially on a busy highway. Conversely, accidents that result in airbag deployment or the inability of the engine to physically remain running may be ideal candidates for the fuel pump to be disabled. Ultimately, disabling the fuel pump during a severe crash is a safety protocol that could prevent an existing fire from being fed if the fuel line is severed.
History
Inertia switches were prevalent in the past, but modern day vehicles rely on cam shaft sensors, oil pressure switches, and other sensor feedback to determine if the engine is not running. If not running, the Powertrain Control Module (PCM) will normally remove the ground connection to the fuel pump relay coil to disable the fuel pump.
In the early days spent developing our products, we experimented with a variety of power sources that could deliver 12 VDC to the fuel pump. We no longer use the M7 rear cigarette lighter anymore as other fuse slots are more reliable.
How Vehicles Respond During Crashes
Our understanding of how a vehicle is designed to react during a crash is limited. Without the ability to crash test our own fleet of vehicles (and do so safely while capturing usable data), we must rely on our own research. Normally, the loss of cam shaft sensor, oil pressure, or other sensor feedback indicates the motor is not running, which in turn forces the PCM to remove power to the fuel pump via the fuel pump relay. In a similar manner, many vehicles sense other variables, forcing the engine to shut off if favorable conditions are not met (not able to detect a key fob, system faults, etc.)
Severed Fuel Lines
Another unique situation that must be explored is a severed fuel line, which could result from striking an object in the road while driving. In this situation, the fuel pump will pump fuel onto the road. Due to the lack of fuel reaching the fuel injectors, the engine will eventually stall and the cam shaft or oil pressure sensors should remove power to the pump via the fuel pump relay (despite the key position in the ignition).
How Our Products Work
Our products obtain their bypass power source most often from M37, which is the run/start circuit. Our exploration of the TIPM indicates power is likely removed from this circuit when the PCM also attempts to remove power to the fuel pump relay during a crash (despite our inability to crash test vehicles to 100% confirm our research). Products such as our TIPM Plug-In Relay System are powered via a ground wire connection that can optionally be attached to the same ground wire that feeds the original faulty fuel pump relay coil (connector C1 pin 40). Therefore, products like this can be configured to 100% remove power to the pump during a crash event where the engine is not running, maintaining the original safety configuration.
This topic is complex, so feel free to call or email if you have questions.