How Do You Test a Fuel Pump Relay Circuit? The importance behind testing a fuel pump relay circuit is to confirm that the fuel pump is receiving the correct power to operate efficiently. If the relay itself is malfunctioning, the pump may not be able to deliver fuel during operation, resulting in issues such as difficulty starting, engine stalling, or poor performance. For this test, all you need is a multimeter and a jumper wire (20 to 30 minutes to perform this test).
47944-211028}} — Locate the fuse box and see if a relay behind the fuse box can be found. This part is generally located in the engine bay fuse box. Refer to the vehicle’s manual for its exact location, as some cars have the same relays for different systems. Relays control the power to the fuel pump and run on 12 to 14 volts.
Take out the relay and check it for visual damage. Internal failure is often signaled by burn marks, corrosion or melted plastic. With a multimeter, check the resistance of the relay’s coil by placing the probes into the appropriate terminals (usually labeled 85 and 86). Test the relay for resistance A healthy relay should show resistance between +/- 50-200 ohms. Values outside this range could mean that the relay is faulty.
The next thing is to use a jumper wire to bypass the relay and then test the circuit. Attach jumper wire to terminals supplying power to fuel pump (typically 30 and 87). If the pump does come on, then the relay is most likely bad and needs replacing. A new relay priced ★$10 – $40★10 to $40 dollars requires cheaper repairing than performing a full-time diagnostic service.
To check the circuit would work, use the multimeter and measure voltage at the relay’s power supply input. With the ignition in the “ON” position (not the engine) the multimeter (set to volts) will read 12 to 14 volts. In that case, the wiring or the vehicle’s control module is at fault.
There is also a necessity to test the relay under load. Plug the relay back in, start the engine, and measure the voltage at the pump terminals. If the voltage drop is significant (greater than 0.5 volts), there is a poor connection in the circuit, typically due to corroded wires. Regular cleaning or replacing damaged components can assure that power delivery remains uniform.
“The diagnosis of relays and circuits is simple if you have the right tools,” advises automotive expert ChrisFix. Neglecting these small components can cause big issues.” Testing A new relay and changing a bad one on time can prevent tens of thousands of dollars spend on fuel pump replacements and greatly increases your vehicle performance.
Visit Fuel Pump for premium fuel pump components and diagnostic tools. A neglected relay circuit leads to inefficient operation of the fuel system and a shortened life of the pump.