First, check for a blown fuse. Normally, there is a fuse protecting the fuel pump relay; and when the fuel pump doesn’t get power, it usually points to a blown fuse. For instance, on a Honda Civic, power loss to the fuel pump might occur if the 15-amp fuse dedicated to the fuel system is blown. This can be confirmed by a simple visual check at the fuse box. If the fuse has not blown, continue to the following step.
Take a multimeter reading at the electrical connector on the fuel pump for voltage. The reading you should expect to get across the fuel pump terminals should be close to 12 volts once the ignition is in the “on” position. For example, in a Ford Mustang, if the reading is less than 12 volts, there might be a problem with the power feed to the fuel pump. No voltage on the fuel pump means that the fuel pump is not being fed power and would most likely pinpoint problems to the fuel pump relay, wiring, or the engine control module itself.
The next step in troubleshooting is checking the fuel pump relay. The fuel pump relay is the switch that enables power from the battery to reach the fuel pump when the engine is cranked. If the relay is defective, the fuel pump will not work. For instance, a no-start condition may arise in a Chevrolet Silverado if the relay is defective. The relay can be checked by swapping it with a similar relay in the fuse box of the vehicle or with a multimeter for checking continuity upon the activation of the relay.
Another important thing is checking the wiring between the fuel pump, the relay, and the ECM. Disconnection, fraying, and corrosion might occur over time, causing an interruption to power. A Toyota Camry with some problem in wiring may show the tendency of intermittent power to the fuel pump, resulting in hard cold starts. This can be diagnosed by a visual inspection and a continuity test, where one can find a broken wire or poor connections. Damaged wiring replacements or repairs can restore proper power to the fuel pump.
Another thing that could be a factor is the fuel pump inertia switch, which is designed to shut off the fuel supply in case of an accident. For instance, on Ford Explorers, it might just be the inertia switch that has tripped and killed power to the fuel pump to prevent leakage of fuel in such instances. The switch simply needs to be reset if it has been activated.
Sometimes, the cause may be the ECM. The ECM controls the fuel pump relay and triggers it to energize the pump to turn on. If the ECM is faulty, then sometimes it may not send a proper signal to the fuel pump relay for it to get power. A diagnostic scan tool can be utilized to see if the ECM has stored any type of error code that could indicate an issue with the relay circuit or fuel system control.
The power loss check to the fuel pump should be done in a step-by-step manner: starting from the fuse, then voltage testing at the pump, checking the relay, wiring inspection, and verification that the Fuel Pump inertia switch and ECM are functioning properly. By practice of regular maintenance and quick diagnosis of electrical faults, power-related failures can be avoided so that the correct amount of fuel is supplied to the engine for its smooth working.