If any of the various electrical systems in your car are not functioning, a fuel pump can become stuck in either the "ON" or "OFF" position. A common reason for this problem to occur is because of a bad fuel pump relay. More specifically, this is the relay which regulates power that goes to your fuel pump, and can fail with its contacts stuck closed, allowing the pump to run even when the car is off. A relay is designed to run off 12 volts but if the components inside the relay start to fail or short it will lock in the "ON" state. Based on the reports from auto technicians, about 10 to 15% of fuel pump problems are really caused by a relay failure.

The ignition switch may be the cause. One of the systems it controls is the fuel pump. If the switch does not cut power as it is intended, the fuel pump will continue running. In cars over 100,000 miles old, ignition switch wear is a frequent cause of shutdown systems not working. Keep in mind that an ignition switch can cost about $150-$300 for the parts only for your car's make and model but is a worthwhile investment to avoid wearing out your fuel pump before its time.

Fuel Pump ControlRelatively new car models also have a fuel pump relay circuitry that is controlled by the Engine Control Unit. In case the ECU is faulty or it is supplied with wrong information, then even when you turn off the engine, it will most likely send signals to the fuel pump for staying ON. In fact, some recalled for programming were quite high profile such as the may 2019 recall by Nissan that covered around 90k vehicles due to bad ECU software. As a result of the software glitch, electricity was able to flow to the fuel pump even after the engine had been turned off, and this showed how a mistake with digital code would be deadlier when it cascaded down to fuel system parts.

Shorts in the wiring to the fuel pump are another likely cause. A short circuit jumps around the control systems such as relay, ECU etcetera making power always go to the pump. Sometimes this happens when the insulation around a wire wears out from heat or vibration and the bare wires touch making a direct connection. We do this because we can see a 5-10% variation in voltage that could trigger the pump to continue running.

Automotive guru Lee Iacocca was one of the first to point out that, “The skill to identify opportunities and relocate different instructions is the secret of maintaining a competitive edge.” In the same way, early detection of electrical problems in the fuel system can help to avoid serious mechanic failures. Dealing with a stuck fuel pump immediately saves the car owner from a replacement of a burnt-out fuel pump as well as any battery drain problems that can be forced simply improves, (e.g., the pump constantly and unnecessarily runs).

How a Stuck Fuel Pump Causes Battery to Drained, How To Start Your Car's Engine — The Complete Guide In One Place? The pump pulls power from the battery all of the time, and when parked for more than a day or two, that can kill your battery. Not only does this kill the battery, but it will eventually shorten the overall lifespan of a battery that should be good for about 3-5 years and may end up lasting less if is frequently drained due to a failed fuel pump. If your car always has a dead battery (assuming there is nothing wrong with the ignition), ask a mechanic to look for fluctuating alternator charging current.

To learn more about diagnosing and fixing fuel system faults, such as the fuel pump failing, you can visit Fuel Pump.