Pickup 4WD V6-2972cc 3.0L SOHC (1991)
Main Relay (Computer/Fuel System): Description and Operation
Control Relay Location
Control Relay
The control relay, located in the right kick panel, is both and input and output device for the ECU. It supplies the positive circuit to the EGR and purge
solenoids, air flow sensor, ECU and injectors.
When the key is in the START position, current flows from the ignition switch through the control relay coil C2 to ground. This turns on control relay
switch S2, supplying battery voltage to the fuel pump. Once the engine starts and the key is in the ON position, the ECU supplies the ground circuit to
the control relay coil C3, keeping control relay switch S2 closed, energizing the fuel pump. When switch S2 is closed, battery voltage is also supplied to
the ECU so that the ECU detects the power supply to the fuel pump. Additionally, whenever the ECU detects this power supply (switch S2 closed), it
will supply the ground circuit to control relay coil C1. This closes the control relay siwtch S1, suppl;ying power to the ECU and various other
components (injectors, relays and sensors). In the event of engine stall or other abnormal conditions, the ECU will interupt the ground supply to control
relay C1, opening control relay switch S2. This will turn the fuel pump OFF.
NOTE: Failure of the control relay may interrupt power supply to the fuel pump, injectors and/or the ECU, resulting in start failure.
