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MFI Relay

  1. This step checks ignition switch supply voltage of MFI relay. Disconnect MFI relay harness connector. Turn ignition on. Using DVOM, measure voltage between terminal No. 5 of relay harness connector and vehicle ground. See Fig 1 . If voltage is battery voltage, go to step 2). If voltage is not battery voltage, check and repair circuit between ignition switch and MFI relay.
  2. This step checks continuity of MFI relay ground circuit. Turn ignition off. Using DVOM, check continuity between MFI relay harness connector terminal No. 7 and vehicle ground. If continuity exists, go to step 3). If continuity does not exist, check and repair circuit between MFI relay and vehicle ground.
  3. This step checks battery supply voltage of MFI relay. Using DVOM, measure voltage between terminal No. 1 of relay harness connector and vehicle ground. If voltage is battery voltage, go to step 4). If voltage is not battery voltage, check and repair circuit between battery and MFI relay.
  4. This step checks continuity of circuit between MFI relay and ECM. Disconnect ECM harness connector. Check continuity between MFI relay harness connector terminal No. 2 and ECM terminals No. 2and 15 of connector C50-4 on California models or terminals No. 9 and 4 of connector C50-3 on Federal models. See Figure , Figure and Fig 1 .
  5. If continuity exists, harness is okay. Go to step 6). If continuity does not exist, check and repair circuits between MFI relay harness connector and ECM.
  6. This step checks continuity of MFI relay. Removal of relay may assist in testing. Measure resistance between terminals No. 2 and 8 and between terminals No. 3 and 8. Resistance should be about 95 ohms. Measure resistance between terminals No. 6 and 7. Resistance should be about 35 ohms. Measure resistance between terminals No. 5 and 7. Continuity should exist in only one direction. Replace MFI relay if any measurements are not as specified.
  7. Connect 12-volt power source between relay terminals No. 6 and 7. Connect positive lead to terminal No. 6. With relay energized, continuity should exist between terminals No. 1 and 4. With power source removed, continuity should not exist.
  8. Move 12-volt power source to relay terminals No. 5 and 7. Connect positive lead to terminal No. 5. With relay energized, continuity should exist between terminals No. 1 and 3. With power source removed, continuity should not exist. Replace MFI relay if any measurements are not as specified.
    Fig 1: Identifying MFI Relay Connectors (Precis)
    G93E78455Courtesy of MITSUBISHI MOTOR SALES OF AMERICA.
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