ENCLOSURE GP. 1921147 - Caterpillar

Illustration 1 g02157398
Schematic of the service brake accumulator pressure sensorThis diagnostic code is associated with the service brake accumulator pressure sensor. The FMI 04 diagnostic code means that the brake ECM has determined that voltage or duty cycle of the sensor circuit is below normal. The position sensor is an active analog sensor that sends a voltage signal to ECM to indicate hydraulic pressure in service brake accumulator.The possible causes of this diagnostic code are listed below:
The signal circuit for the sensor is shorted to ground.
The sensor has failed.
The ECM has failed. ECM failure is unlikely. Note: Before performing this procedure, inspect the harness connectors that are involved in the circuit. Poor connections can often be the cause of a problem in an electrical circuit. Verify that all connections in the circuit are clean, that all connections are secure and that all connections are in good condition. If a problem with a connection is found, correct the problem and verify that this diagnostic code is active before performing this procedure.Note: The following test procedure may create other diagnostic codes. Ignore these created diagnostic codes and clear the diagnostic codes when the original diagnostic code has been corrected. Ensure that the diagnostic code of CID 1961 FMI 04 is active before performing this procedure. Note: Use a calibrated 146-4080 Digital Multimeter for the measurements in this procedure.Test Step 1. CHECK THE SIGNAL CIRCUIT OF THE SENSOR FOR A SHORTThe sensor remains disconnected from the harness. The disconnect switch and the keyswitch remain in the OFF position. The harness connectors remain disconnected from the brake ECM.
Turn the disconnect switch and the keyswitch to the OFF position.
Disconnect the service brake accumulator pressure sensor from the harness.
Disconnect the harness connectors J1 and J2 from the brake ECM.
At the harness connector J2 for the brake ECM, measure the resistance between signal contact J2-50 (wire 432-PK) and all of the other contacts that are used on the J1 and J2 connectors of the brake ECM.Expected Result:Each resistance is greater than 5000 ohms.Results:
OK - Each resistance is greater than 5000 ohm. The measurements do not indicate that the accumulator pressure sensor circuit is shorted to a ground source. Proceed to Test Step 3.
NOT OK - A resistance is less than 5000 ohms. There is a short in the harness.Repair: The wire for the sensor signal circuit 432-PK is shorted to the frame ground or to the circuit in the harness with the low resistance.Refer to the complete Electrical Schematicof the machine. Check all of the connections in the circuits. Examine the harness for indications of damage. Damage to the harness connector could indicate a location for a short circuit.For information on testing for short circuits and finding short circuits, refer to Testing and Adjusting, "Wiring Harness (Short Circuit) - Test". Repair or replace the harness.STOPTest Step 2. CHECK THE SIGNAL AT THE SENSOR.The keyswitch and the disconnect switch remain in the OFF position.
Reconnect the harness connectors to the brake ECM.
At the harness for the sensor connector,