The fuel pump relay could fail to be working properly due to various conditions such as failure to start, stalling, or improper performance of an engine. Commonly misdiagnosed, these symptoms usually have the fuel pump at fault. The fuel pump relay works on an electrical basis and manages the flow of power to the fuel pump so it can work whenever the engine is turned on. Thus, when the relay fails, it can completely block the fuel pump from getting power to feed the engine with fuel.
The first evidence of a faulty fuel pump relay might be demonstrated by difficulty in starting the vehicle. The absence of power in a properly functioning fuel pump would keep the fuel from reaching the engine if the relay is not operating correctly. These vehicle models, such as the F-150, usually act this way when the fuel pump relay goes bad, and the car sometimes would start and sometimes wouldn’t, according to Ford. Diagnostic tools for reading OBD-II codes may return the trouble codes P0230 or P0231, related to the fuel pump relay or circuit.
The fuel pump relay failure can also be noticed by checking the no-fuel condition in the engine. One symptom could be that the engine may well crank but not fire. That is if the relay has actually failed and stopped sending power out to the fuel pump. In such cases, AAA Automotive recommends trying a multimeter as a tester for continuity. A properly functioning relay should allow current to pass through, while a faulty relay will show no continuity. Typically, a fuel pump relay lasts between 5 to 10 years but can fail prematurely due to excessive wear, heat exposure, or electrical surges.
Listening for unusual sounds is another method to detect a faulty relay. If you hear a whining sound or no sound after the ignition is turned on, it may indicate that the fuel pump is not getting power due to a relay problem. A good fuel pump will normally make a slight humming sound for a few seconds once you turn the ignition on to pump up the system. If no sound is produced, it may be due to the relay.
Besides, a general look at the relay would also give a hint as to whether or not it’s faulty. Sometimes, a burnt or damaged relay can be identified by sight. High temperatures, wear and tear, or a short circuit could lead to the malfunction of its internal parts. For example, Toyota stated that some models like the Corolla were prone to problems of fuel pump relays burning out because of accumulated internal heat and ultimately leading to total failure. Replacing a bad fuel pump relay usually runs in the area of $50 to $150 depending on the vehicle make and model.
Other times, the problem can be diagnosed by simply exchanging the relay with another relay of the same type that controls a function such as the air conditioning or the headlights. If the vehicle now starts after the swap, then the relay is the likely culprit. Many times, Chrysler recommends this procedure when attempting to diagnose problems with the fuel pump relay in some of its vehicles.
Finally, a fuel pressure gauge can be used to confirm the fuel pump is not getting power from a malfunctioning relay. This gauge gives the pressure in the fuel system, which, if abnormally low or completely nil, means the fuel pump is likely not working as expected. At this point, the fuel pump relay could be checked as a likely cause.
A faulty fuel pump relay can exhibit a wide range of symptoms, such as not being able to start, an engine that stalls, or bad performance on fuel. The company behind the models mentioned above highly recommends replacing relays in a timely manner. Otherwise, driving a car with a bad relay could lead to greater issues with the fuel pump and generally impact fuel performance.
For more information about Fuel Pump replacements and relays, see Fuel Pump.