CP54B, CP56B, CP68B, CP74B, CS54B, CS56B, CS64B, CS66B, CS68B, CS74B, CS76B and CS78B Vibratory Soil Compactors Machine Electronic Control System Caterpillar

Sensor Signal (Analog, Passive) - Test

Usage:

Machine ECM

The following is a list of diagnostic codes (SPN) that are associated with the passive (analog) circuits of the machine.

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Table 1
Machine ECM (MID 39)
SPN-FMI	Code Description	System Response
96-3	Fuel Level 1: Voltage above normal	Set fuel level to 0 but do not indicate low fuel level event. Not latched. Fault Level - 1
96-4	Fuel Level 1: Voltage below normal	Set fuel level to 0 but do not indicate low fuel level event. Not latched. Fault Level - 1
1638-3	Hydraulic Temperature: Voltage above normal	Set Temp to −40° C (−40° F). Set Fan speed to "Max". Fault Level - 1
1638-4	Hydraulic Temperature: Voltage below normal	Set Temp to −40° C (−40° F). Set Fan speed to "Max". Fault Level - 1

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 3 diagnostic code are:

The return circuit is open.
The signal circuit is open or the sensor is disconnected.
The signal circuit is shorted to the +battery.
The sensor has failed.
The ECM has failed. A failure of the ECM is unlikely.

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.

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Illustration 1	g03819430
Passive Analog sensor connections

The diagram above is a simplified schematic of the Machine ECM connections. The schematic is electrically correct. However, not all of the possible harness connectors are shown.

For the full Electrical Schematic of the Soil Compactors in this manual, refer to the appropriate media listed below.

For models CS54B and CP54B refer to Electrical Schematic, UENR6386.
For models CS56B, CP56B, CS64B, CS66B, CS68B and CP68B refer to Electrical Schematic, UENR6388.
For models CS74B, CP74B, CS76B and CS78B refer to Electrical Schematic, UENR6384.

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Table 2
Float Position	Float Height (mm) ⁽¹⁾	Resistance (Ω)
Full Stop	53 mm (0.174 ft)	25-29
Full	60 mm (0.197 ft)	35-39
3/4	108 mm (0.354 ft)	67
1/2	172 mm (0.564 ft)	103
1/4	245 mm (0.804 ft)	153
Empty	284 mm (0.932 ft)	200-210
Empty Stop	300 mm (0.984 ft)	240-250

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⁽¹⁾	Float height is measured from the top of the float to the bottom of the mounting flange.

The table above is a reference that can be used when checking the resistance of the Fuel Sensors.

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Table 3
Temperature	Resistance (Ω)
100° C (212° F)	68
75° C (167° F)	148
50° C (122° F)	360
25° C (77° F)	1000
0° C (32° F)	3268

The table above is a reference that can be used when checking the resistance of the Hydraulic Oil Temperature Sensor.

Diagnostic Trouble Code Procedure

Note: 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.

Identify the active FMI code associated with the components.
Determine which code is present and use the list below to determine which procedure to follow.

FMI 3 diagnostic code, proceed to Table 4.
FMI 4 diagnostic code, proceed to Table 5.

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Table 4
FMI 3 Troubleshooting
Troubleshooting Test Steps	Values	Results
1. Check The Sensor Note: Refer to the tables above for a list of resistance values related to specific values. A. Turn the key start switch and the disconnect switch to the OFF position. B. Disconnect the sensor from the harness. C. Measure the resistance between pin 1 and 2 of the sensor.	The resistance reading agrees with the values from the table.	OK - The resistance readings agree with the values in the table. Proceed to Test Step 2. NOT OK - The resistance readings do not agree with the values in the table. Repair: Replace the sensor. Proceed to Test Step 4.
2. Check For An Open In The Sensor Circuit A. The key start switch and disconnect switch remain in the OFF position. B. The harness connector remains disconnected from the sensor. C. At the sensor harness connector, install a jumper wire across pins 1 and 2. D. Disconnect the connector from the ECM. E. At the ECM harness connector, measure the resistance between the signal and return contacts for the sensor.	The resistance reading is less than 5 Ω.	OK - The resistance is less than 5 Ω. Proceed to Test Step 3. NOT OK - The resistance is greater than 5 Ω. The open is in the signal circuit or the return circuit. Repair: Repair or replace the harness. Proceed to Test Step 4.
3. Check The Signal Circuit For A Short. A. The disconnect switch and the key start switch remain in the OFF position. B. The harness connector remains disconnected from the ECM. C. Remove the jumper wire from the sensor harness connector. D. At the ECM harness connectors, measure the resistance between the signal circuit and all the other contacts that are used on the ECM.	Each resistance reading is greater than 5K Ω.	OK - Each measurement is greater than 5K Ω. Proceed to Test Step 4. NOT OK - A resistance measurement is less than 5 Ω. A short exists between the signal circuit and the circuit with the low resistance measurement. Repair: Repair or replace the machine harness. Proceed to Test Step 4.
4. 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 ON. C. Clear all diagnostic codes. D. Operate the machine. E. Stop the machine and engage the safety lock. F. Check if the diagnostic code is active.	The diagnostic code is no longer present.	OK - The diagnostic code does not exist at this time. 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 Caterpillar. 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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Table 5
FMI 4 Troubleshooting
Troubleshooting Test Steps	Values	Results
1. Check The Sensor A. Turn the key start switch and disconnect switch ON. B. Ensure that the diagnostic code is active. C. Disconnect sensor from 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 OFF. 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 that are used on the ECM.	Each reading 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 that is greater than 5 Ω but less than 5K Ω would indicate a loose connection or a corroded connection in the circuit. A resistance measurement that is greater than 5K Ω would indicate 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 ON. C. Clear all diagnostic codes. D. Operate the machine. E. Stop the machine and engage the safety lock. F. Check if the diagnostic code is active.	The diagnostic code is no longer present.	OK - The diagnostic code does not exist at this time. 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 Caterpillar. This consultation may effect repair time. Follow the steps in Troubleshooting, "ECM - Replace" if the ECM needs to be replaced. STOP.