BOSS 8R3857 - Caterpillar

Illustration 1 g01942314
Schematic for the Boost Relay
This diagnostic code is associated with the Boost Relay. The FMI 03 means that the ECM has determined that the voltage of the relay circuit is above normal.The possible causes of the diagnostic code are listed:
The energize circuit of the relay is shorted to the +battery.
The ECM has failed. This situation is unlikely.Note: The following test procedure may create other diagnostic codes. Ignore these created diagnostic codes and clear these diagnostic codes when the original diagnostic code has been corrected. Ensure that the diagnostic code of SPN 5012 FMI 03 is active before performing this procedure.Note: Use the 146-4080 Digital Multimeter for the measurements in this procedure.System Response:The machine response is listed:
The Boost Relay may be stuck ON.
Machine performance may decrease when lifting small scrap.Note: Before performing this procedure, verify that all circuit breakers and fuses in the charging circuit and the ECM system supply circuit are closed. If a problem with a circuit breaker or a fuse is found, correct the problem. Verify that this diagnostic code is active before performing this procedure.Test Step 1. CHECK THE STATUS OF THE DIAGNOSTIC CODE
Turn the disconnect switch and the key start switch to the OFF position.
Inspect the harness connectors. Clean the contacts of the harness connectors. Check the wires for damage to the insulation that is caused by excessive heat, corrosion, or chafing.
Perform a 45 N (10 lb) pull test on each of the wires that are associated with the circuit.
Use the Cat Electronic Technician (ET) service tool to perform a “Wiggle Test” on the machine wiring harness. The wiggle test can detect intermittent shorts or opens in the machine wiring harness.
Reconnect all harness connectors. Make sure that the connectors are fully seated. Observe that the clips for each connector are fastened securely.
Turn the disconnect switch and the key start switch to the ON position.
Operate the machine.
Determine if the SPN 5012 FMI 03 diagnostic code is still active.Expected Result:The SPN 5012 FMI 03 diagnostic code is still active.Results:
YES - The SPN 5012 FMI 03 diagnostic code remains active. Proceed to Test Step 2.
NO - The SPN 5012 FMI 03 code is not active. The problem does not exist at this time.Repair: The initial diagnostic code was probably caused by a poor electrical connection or a short at one of the harness connectors. Resume normal machine operation.STOPTest Step 2. CHECK THE HARNESS FOR AN OPEN
Turn the disconnect switch and the key start switch to the OFF position.
Disconnect the Wire (C905-OR(Orange)) from the A terminal for the Boost Relay.
Disconnect the Wire (A272-BK(Black)) from the B terminal for the Boost Relay.
Place a jumper from Boost Relay wire (C905-OR(Orange)) to Boost Relay wire (A272-BK(Black)).
Disconnect the J2 connector at the ECM.
Measure the resistance from contact J2-2 (wire C905-OR(Orange)) to J2-4 (wire A272-BK(Black)).Expected Result:The resistance is less than 5 ohms.Results:
OK - The resistance is less than 5 ohms. The harness has continuity in the circuit. Proceed to Test Step 3.
NOT OK - The resistance is greater than 5 ohms.Repair: The