RECTIFIER AS 2539808 - Caterpillar

Illustration 1 g01948293
Schematic of the pressure sensor (left parking brake oil)
This diagnostic code is associated with the pressure sensor (left parking brake oil). The FMI 04 diagnostic code means that the Brake ECM has determined that the voltage of the circuit for the position sensor is below normal. The pressure sensor is a PWM sensor with an operating duty cycle from 0% to 100%. The sensor has an operating pressure range from 0 kPa (0 psi) to 5871 kPa (852 psi). The relation between the pressure and the duty cycle is linear.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. This is unlikely. 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 1225 FMI 04 diagnostic code is active before performing this procedure. Note: Use the 146-4080 Digital Multimeter for the measurements in this procedure.System Response:The diagnostic code will be logged into memory.Test Step 1. CHECK THE SENSOR
Turn the disconnect switch and the key start switch to the ON position.
Ensure that the diagnostic code is active.
Observe the status of the diagnostic code. Disconnect the sensor from the machine harness. Expected Result:The CID 1225 FMI 04 diagnostic code remains active. Results:
OK - The diagnostic code remains active. The sensor is correct. Proceed to Test Step 2.
NOT OK - The diagnostic code is no longer active. The sensor has failed.Repair: Replace the sensor.STOPTest Step 2. CHECK THE WIRING HARNESS OF THE SENSOR FOR A SHORT TO GROUND.
Turn the key start switch and the disconnect switch to the OFF position.
Disconnect the machine harness from the sensor.
Disconnect the machine harness connector(s) from the ECM.
At the machine harness connector for the ECM, measure the resistance from the signal contact J2-16 (wire H428-BK(Black)) of the machine harness to all possible sources of ground. Measure the resistance to all contacts of the machine harness connectors for the ECM. Expected Result:Each resistance measurement is greater than 5000 ohms.Results:
OK - Each resistance measurement is greater than 5000 ohms. The machine harness is correct. Proceed to Test Step 3.
NOT OK - One or more resistance measurements is not correct. There is a short in the machine harness. Repair: The short is between signal contact J2-16 (wire H428-BK(Black)) and the circuit with the low resistance measurement. Repair the machine harness or replace the machine harness.STOPTest Step 3. CHECK IF THE DIAGNOSTIC CODE REMAINS.
Inspect the contacts of the harness connectors and clean the contacts.
Reconnect all harness connectors.
Turn the disconnect switch and the key start switch to the ON position.
Operate the machine.
Check the status of the CID 1225 FMI 04 diagnostic code. Expected Result:The CID 1225FMI 04 diagnostic code is active. Results:
YES - The CID 1225 FMI 04 diagnostic code is active. The diagnostic code has not been corrected. The ECM may have failed.Repair: It is unlikely that