538, 548 and 558 Forest Machine Sensor Signal (Analog, Passive) - Test Caterpillar


Sensor Signal (Analog, Passive) - Test
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538, 548 and 558 Forest Machine [M0066266]
ELECTRICAL AND STARTING SYSTEM
SENSOR GP
1.1. Machine ECM
2.1. Diagnostic Trouble Code Procedure

Machine ECM

The following is a list of Diagnostic Trouble Codes (DTC) associated with the passive (analog) circuits of the machine.

Table 1
Machine ECM (MID 299) 
DTC  Code Description  System Response 
96-4  Fuel Level Sensor : Voltage Below Normal  Fuel gauge indicator will report incorrectly. 
600-4  Hydraulic Oil Temperature Sensor : Voltage Below Normal  Hydraulic Oil Temperature indicator will report incorrectly. 

A passive analog sensor contains an internal resistor. The change in resistance of the internal circuit results in a change of voltage that is detected by the electronic control module.

Possible causes for an FMI 4 diagnostic code are:

  • The sensor has failed.

  • The signal circuit for the sensor is shorted to ground.

  • The ECM has failed. A failure of the ECM is unlikely.


Illustration 1g03721272
Schematic of the Fuel Level Sensor and Hydraulic Oil Temperature Sensor

The preceding diagram is a simplified schematic of the passive analog sensor connections. The schematic is electrically correct. However, not all the possible harness connectors are shown. Refer to the latest revision of the Electrical Schematic to view the entire circuitry of the machine.

Table 2
C° Temperature (F°)  Resistance (Ω) 
−40° C (−40° F)  33650 
−25° C (−13° F)  13052 
−10° C (14° F)  5538 
0° C (32° F)  3268 
10° C (50° F)  1991 
25° C (77° F)  1000 
40° C (104° F)  436 

Table 3
Float Position  Resistance (Ω) 
Full  7.5-9 
3/4  21 
1/2  33.8 
1/4  53 
Empty  82-85 

The tables above are a reference to check the resistance of the passive analog sensors.

Diagnostic Trouble Code Procedure

Prior to beginning 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.

  1. Identify the active FMI 4 code associated with the components.

  • FMI 4 diagnostic code, proceed to Table 4.

Table 4
FMI 4 Troubleshooting 
Troubleshooting Test Steps  Values  Results 
1. Check The Sensor

A. Turn the key start switch and disconnect switch to the ON position.

B. Ensure that the diagnostic code is active.

C. Disconnect the sensor from the machine harness.
 

The diagnostic code remains active. 
OK - Diagnostic code remains active.

Proceed to Test Step 2

NOT OK - Diagnostic code is no longer active.

Repair: Replace the sensor.

Proceed to Test Step 3. 
2. Check The Wiring Harness Of The Sensor For A Short To Ground

A. Turn the key start switch and the disconnect switch to the OFF position.

B. Disconnect the machine harness connector from the sensor.

C. Disconnect the machine harness connectors from the ECM.

D. At the ECM harness connectors, measure the resistance between the signal circuit and all the other contacts used on the ECM. 

Each reading is greater than 5K Ω. 
OK - All resistance readings are greater than 5K Ω.

Proceed to Test Step 3.

NOT OK - One or more of the readings are less than 5 Ω. A short exists between the signal contact and the circuit with the low resistance.

Repair: Repair or replace the machine harness.

Note: A resistance greater than 5 Ω but less than 5K Ω indicates a loose or corroded connection in the circuit. A resistance measurement greater than 5K Ω indicates an open in the circuit.

Proceed to Test Step 3. 
3. Check If The Diagnostic Code Remains

A. Reconnect all harness connectors. Return machine to normal operating condition.

B. Turn the key start switch and the disconnect switch to the ON position.

C. Clear all diagnostic codes.

D. Operate the machine.

E. Stop the machine and engage the safety lock lever.

F. Check if the diagnostic code is active. 

The diagnostic code is no longer present. 
OK - The diagnostic code does not exist currently. The initial diagnostic code may have been caused by poor electrical connection or short at one of the harness connections. Resume machine operation.

STOP

NOT OK - The diagnostic trouble code has not been corrected. If the diagnostic code has not been corrected after performing the procedure a second time, the ECM may require replacement.

Prior to replacing the ECM, always contact the Technical Communicator at your dealership for possible consultation with AVSpare. This consultation may effect repair time.

Follow the steps in Troubleshooting, "ECM - Replace" if the ECM needs to be replaced.

STOP 

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