Cherokee 4WD L4-150 2.5L VIN P MFI (1991)
Fuel Pump Relay: Description and Operation
Power Distribution Center
This relay has battery voltage applied to it from the ignition switch. The engine controller controls this relay by applying or taking away the ground from
its circuit. When the ground is applied, the relay is energized, and voltage is allowed to flow through the fuel pump ballast resistor to the fuel pump (in
all engine operating modes except wide open throttle). When the vehicle is experiencing a wide open throttle condition, the ballast bypass relay is
ENERGIZED and the fuel pump ballast resistor is bypassed, allowing full system voltage to be applied to the fuel pump. The fuel pump ballast relay is
used to lower the voltage going to the fuel pump, reducing the fuel pump operating noise level.
This relay is located in the power distribution center next to the coolant recovery bottle. This relay also controls the voltage that goes to the oxygen
sensor heating element.
