Fuel Pump Control Unit: Testing and Inspection
CHECKING FLOAT SWITCHRemoving Rear Seat Cushion:
1. Depress the buttons under the front of the rear seat and remove the rear seat cushion.
Disconnecting Transfer Pump And Float Switch Connector:
2. Disconnect transfer pump connector and remove access cover.
Checking Float Switch:
3. Remove transfer pump tank unit and check continuity through float switch, as shown in illustration.
^ Should have continuity only when float is in the bottom position.
If switch does not operate as described, replace it.
Removing 4X4 Control Unit:
4. Reconnect tank unit. Remove and disconnect 4X4 control unit (under drivers seat).
Checking Continuity To Ground Through Float Switch And Wiring:
5. With float in bottom position, check continuity between control unit harness connector terminal "M" and ground, as shown in illustration.
^ Should have continuity.
6. Raise float, and check again for continuity.
^ Should have no continuity.
If results are not as described, check wiring between control unit and float switch for open or shorts to ground. Also check that float switch has a good ground connection. If wiring is OK, replace float switch.
CONTROL UNIT
Removing 4X4 Control Unit:
1. Turn 4X4 control unit over and re-connect.
Checking Control Unit While Simulating Float Switch Operation:
2. Turn ingition "ON".
3. With transfer pump tank unit disconnected, ground terminal "M" of control unit, while monitoring voltage at terminal "N".
^ Should have no voltage with terminal "M" of control unit grounded.
4. Disconnect ground jumper from control unit.
^ After approx. 10 seconds, voltage should go to battery voltage.
If control unit does not operate as described, check control unit power supply and ground connections. See CENTER DIFFERENTIAL LOCK SYSTEM under CHASSIS ELECTRICAL DIAGRAMS
If wiring is OK, replace 4X4 control unit.