Main Relay (Computer/Fuel System): Testing and Inspection

OPERATION
- While the ignition switch is on, battery power is supplied to the engine control module, the injector, the volume air flow sensor, etc.
- When the ignition switch is turned on, the battery voltage is applied from the ignition switch to the engine control module, which then turns ON the power transistor to energize the MFI relay coil. This turns ON the MFI relay switch and the power is supplied from the battery to the engine control module through the MFI relay switch.





INSPECTION
Using Scan Tool

















HARNESS INSPECTION

NOTE:
*1: (Up to 1995 models)
*2: (From 1996 models)





MFI RELAY INSPECTION
(1) Remove the MFI relay.





(2) Check for continuity between MFI relay terminals.





(3) Using jumper wires, connect terminal (7) of MFI relay to battery (+) terminal and terminal (5) of MFI relay to battery (-) terminal.

CAUTION:
- If jumper leads are not connected properly, the relay will be damaged.





(4) Connecting and disconnecting the jumper wire to battery (-) terminal, measure the voltage at terminal (1) of the MFI relay.





(5) Using jumper wires, connect terminal (8) of MFI relay to battery (+) terminal and terminal (6) of MFI relay to battery (-) terminal.





(6) Connecting and disconnecting the jumper wire to battery (-) terminal, check the continuity across terminals (2) and (4) (or (3) and (4) of the MFI relay.
(7) Replace the MFI relay if any defect is evident.