12886A 6 Mercury SWITCH

Illustration 1 g02251074
Schematic for the fuel pressure differential pressure switch
Test Step 1. Inspect the Electrical Connectors and the Wiring
Turn the keyswitch to the OFF position.
Illustration 2 g02251713
Left side engine view (typical example)
(1) J2/P2 ECM connectors
Illustration 3 g02251794
Typical location of the fuel filter differential pressure switch (right front engine view)
(2) Fuel filter differential pressure switch
Thoroughly inspect connector (1). Also, thoroughly inspect the connector for switch (2). Refer to Troubleshooting, "Electrical Connectors - Inspect" for details.
Illustration 4 g02251855
Terminal locations at the P2 ECM connector for the fuel filter differential pressure switch
(P2-49) Fuel filter differential pressure switch
(P2-54) Return
Illustration 5 g01218763
Connector for the fuel filter differential pressure switch
(Terminal 1) Fuel filter differential pressure switch
(Terminal 2) Return for the switch
Perform a 45 N (10 lb) pull test on each of the wires in the ECM connector and the sensor connectors.
Check the allen head screw for each of the ECM connectors for the proper torque. Refer to Troubleshooting, "Electrical Connectors - Inspect" for details.
Check the harness and wiring for abrasions and for pinch points from the sensor to the ECM. Expected Result:All connectors, pins, and sockets are coupled and/or inserted. The harness and wiring are free of corrosion, of abrasion, and of pinch points.Results:
OK - The harness and wiring are OK. Proceed to Test Step 2.
Not OK - There is a problem in the connectors and/or wiring.Repair: Repair the connectors or wiring and/or replace the connectors or wiring. Ensure that all of the seals are properly in place and ensure that the connectors are coupled.Verify that the repair eliminates the problem.STOPTest Step 2. Check the Switch Circuit with no Pressure in the Fuel System
Disconnect the connector for the differential pressure switch.
Check continuity between the terminals for the differential pressure switch at the connector. Expected Result:The resistance check indicates a short circuit.Results:
OK - The resistance check indicates a short circuit. Proceed to Test Step 3.
Not OK - The resistance check indicates an open circuit. There is an open circuit in the fuel filter differential pressure switch.Repair: Replace the differential pressure switch.STOPTest Step 3. Check the Switch Circuit with Pressure in the Fuel System
Turn the keyswitch to the ON position.
Use the "Fuel Pump Relay Command Override" in "Caterpillar" Electronic Technician (ET) to engage the fuel priming pump.
While the fuel priming pump is running, check continuity between the terminals for the differential pressure switch at the connector.
Turn the keyswitch to the OFF position. Expected Result:The resistance check indicates a short circuit.Results:
OK - The resistance check indicates a short circuit. The differential pressure switch is OK. Proceed to Test Step 4.
Not OK - The resistance check indicates an open circuit. There is an open circuit in the wiring for the fuel filter differential pressure switch.Repair: Replace the differential pressure switch.STOPTest Step 4. Check for an Open Circuit in the Harness
Disconnect the J2/P2 ECM connector.
Create a short on the ECM side of the harness between the terminals of the connector for the differential pressure switch.
Check continuity at the ECM connector between terminal P2-49 (fuel filter pressure switch) and terminal P2-54 (return). Expected Result:The resistance check indicates a short circuit.Results:
OK - The resistance check indicates a short circuit. Proceed to Test Step 5.
Not OK - The resistance check indicates an open circuit.Repair: Repair the connectors or wiring and/or replace the connectors or wiring between the ECM and the connector for the differential pressure switch.STOPTest Step 5. Check for a Short Circuit in the Harness
Check continuity at the ECM connector between terminal P2-49 (fuel filter pressure switch) and every terminal on the P1 and P2 ECM connectors. Expected Result:The resistance checks indicate an open circuit.Results:
OK - The resistance checks indicate an open circuit.Repair: Check all connectors and wiring. Ensure that there are clean, solid connections at each connector. Return all wiring to the original configuration and retest the circuit. The most likely cause of the problem is a poor connection. The ECM can be tested by removing the wire P2-49 (fuel filter pressure switch) from the P1 ECM connector. Start and run the engine. After an hour, check for an event code related to the switch. If the event code is activated with the open in place at the ECM connector, there may be a problem with the ECM. Before you consider replacing the ECM, consult the Dealer Solutions Network (DSN).STOP
Not OK - The resistance checks indicate a short circuit.Repair: Repair the connectors or wiring and/or replace the connectors or wiring between the ECM and the connector for the differential pressure switch.STOP