CORE AS-HYDRAULIC OIL COOLER 2154618 - Caterpillar

Possible Causes for an FMI 3 Diagnostic code are:
The power supply circuit for the sensor is open.
The return circuit is open.
The signal circuit is open or the sensor is disconnected.
The signal circuit is shorted to the sensor power supply.
The sensor has failed.
The sensor was activated in Cat ET when the component is not on the machine.
The ECM has failed. An ECM failure is unlikely.Possible Causes for an FMI 4 Diagnostic code are:
The signal circuit for the sensor is shorted to ground.
The sensor has failed.
The ECM has failed. An ECM failure is unlikely.
Illustration 1 g03859739
Power Train ECM Sensor Signal (Analog, Active) schematicNote: The diagram above is simplified schematic of the Implement ECM connections. The schematic is electrically correct. However, not all of the possible harness connectors are shown. Refer to the latest version of the Electrical Schematic for the complete schematic:Reference(PL72 HRC) Electrical System Schematic, UENR5939Reference(PL72 LRC) Electrical System Schematic, UENR5940Reference(PL83 HRC) Electrical System Schematic, UENR4145Reference(PL83 LRC) Electrical System Schematic, UENR4146Reference(PL87 HRC) Electrical System Schematic, UENR4145Reference(PL87 LRC) Electrical System Schematic, UENR4146Diagnostic Trouble Code Procedure
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, secure and 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.
Table 2
Troubleshooting Test Steps    Values    Results    
1. Identify Active DTC Code Associated With Sensor Circuit    
Code present     FMI 3 diagnostic code, proceed to Test Step 2.
FMI 4 diagnostic code, proceed to Test Step 6.    
Begin Process For FMI 3 Troubleshooting HERE    
2. Check The Supply Voltage at the Sensor
A. Turn key start switch and disconnect switch ON.
B. Disconnect the machine harness from sensor.
C. Refer to the schematic to determine the voltage source for the suspected faulty sensor.
D. Measure voltage between supply and return contacts at the machine harness connector for the sensor.    
Voltage is 10.0 0.5 VDC or 5.0 0.5 VDC     OK - The voltage reading is correct for the suspected faulty sensor.
Proceed to Test Step 4.
STOP
NOT OK- The voltage is NOT correct for the circuit.
Repair - If there is an active CID 262 or CID 1482, troubleshoot the code. If there is not an active CID 262 or CID 1482, replace the circuit breaker associated with the sensor.    
3. Check For An Open In The Sensor Circuit
A. The sensor remains disconnected from the machine harness.
B. Turn the key start switch and the disconnect switch OFF.
C. At the harness connector for the sensor, place a jumper wire between the signal contact and frame ground.
D. Disconnect J1 and J2 harness connectors from the ECM.
E. At the machine harness connector for ECM, measure the resistance from the signal contact for the sensor to frame ground.
F. Gently pull on the wire and move the wire in a circular motion at ECM connector and