If the pump doesn’t get the proper voltage, it won’t generate the necessary pressure to supply fuel under ideal circumstances. Voltage range testing is essential, even a small loss of voltage can has a big impact on how well the fuel pump operates, leading to reduced life and overall vehicle performance. A significant voltage drop (more than 0.5 volts) across the pump’s circuit usually points to a problem.
The above test requires a high-accuracy digital multimeter that can measure DC voltage. This begins with switching the multimeter to the DC voltage scale and connecting it across the positive and negative terminals of the pump circuit. The ignition of the vehicle needs to be in the on position and the fuel pump must be working. Under normal conditions, the pump operates at 12 to 14 volts across the circuit.
This requires two key measurements. First you can measure the voltage on the battery terminals to have a baseline which is usually expected to be between 12.4 and 12.7 volts. Then check the voltage at the ending of the fuel pump. The voltage drop is determined by the difference in these readings. A lower reading than the baseline by more than 0.5 volts indicates resistance in the circuit, likely due to corroded connectors, worn wires, or a failing relay.
During the automotive development process, voltage drop testing is the most widely used diagnostic tool because of the clear and diagnostic data it provides. For example, a 2022 casestudy from an auto repair shop showed that technicians discovered a 1.2-volt drop due to a defective ground wire, which when corrected, yielded a noticeable improvement in the pump’s operation and 15% to 40% increase in fuel efficiency.
In maintenance, ethics are all about the use of routine checks. “Preventive maintenance is the key to keeping your car running like new,” said John Haynes, founder of Haynes Manuals. This principle explains why addressing voltage drops early is critical to avoiding expensive fuel pump replacements, which can run anywhere from $200 to $1,000, based on certain makes and models of vehicles.
Read further at Fuel Pump, a guide to drive the fuel industry.