844K Wheel Dozer Caterpillar

Sensor Signal (Analog, Active) - Test

Usage:

844K K4Y

Transmission ECM

This type of sensor is distinguished by the presence of a voltage, ground, and signal connection to complete the sensor circuit. The output of this sensor is a voltage that falls into an expected output range. This sensor is associated with multiple electronic control modules. This sensor is used to measure fuel levels (or other fluids), or brake charge pressure (or other pressures).

The following is a list of active (analog) circuits codes associated with the Transmission ECM.

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Table 1
Transmission ECM (MID 81)
DTC	Code Description	System Response
379-3	Machine Auto Lube Pressure Sensor: Voltage Above Normal	Auto Lube system is disabled.
2984-3	Auto Lube Pump Outlet Pressure Sensor: Voltage Above Normal	Auto Lube system is disabled.
2984-4	Auto Lube Pump Outlet Pressure Sensor: Voltage Below Normal	Auto Lube system is disabled.

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. This situation 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. A failure of the ECM is unlikely.

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Illustration 1	g03651868
Schematic for the Analog, Active Sensors associated with the Transmission ECM.

Note: The diagram above is a simplified schematic of the ECM connections. The schematic is electrically correct, however all possible harness connectors are not shown. Refer to the latest revision of: Electrical Schematic , UENR4996, "844K Wheel Dozer (T4F) Electrical System Schematic" for the complete schematic.Electrical Schematic , UENR1697, "844K Wheel Dozer (LRC) Electrical System Schematic" for the complete schematic.

Diagnostic 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.

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Table 2
Troubleshooting Test Steps	Values	Results
1. Identify Active DTC Code Associated With Sensor Circuit A. Use Cat ^® ET to confirm all logged diagnostic codes for the machine. B. Compare the codes to the codes listed in the tables above.	Code present.	FMI 3 diagnostic code, proceed to Test Step 2. FMI 4 diagnostic code, proceed to Test Step 5.
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 5 ± 0.3 VDC.	OK - The voltage reading is correct for the suspected faulty sensor. Proceed to Test Step 3. STOP NOT OK - The voltage is NOT correct for the circuit. Repair: If there is an active DTC 41, troubleshoot the code. If there is not an active DTC 41, 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 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 observe the resistance readings. Repeat the process for the sensor connector.	The resistance is less than 5 Ω at all times during the manipulation of the harness.	OK - The resistance is less than 5 Ω. The signal circuit and the ground circuits of the sensor are not open in the machine harness. Proceed to Test Step 4. NOT OK - Resistance reading for the signal circuit or the return circuit is greater than 5 Ω. Repair: Check the signal circuit or the ground circuit for opens or bad connections. 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. STOP
4. Check Signal Circuit For A Short To +Battery A. The sensor and the ECM are disconnected from the harness. B. Turn the disconnect switch and the key start switch OFF. C. Remove the jumper wire installed in the previous step. D. Measure the resistance between the signal wire and all +battery wires used in the J1 and J2 harness connectors.	Resistance greater than 5K Ω for all readings.	OK - The resistance is greater than 5K Ω. The harness circuit is correct. Proceed to Test Step 7. NOT OK - The resistance less than 5 Ω. Repair: A short exists in the harness between the +battery and signal circuit. 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. STOP
Begin Process For FMI 4 Troubleshooting HERE
5. Check The Sensor A. With FMI 4 active, disconnect the sensor from the machine harness. B. Observe Cat ET or the Information Display for code change as the sensor is disconnected and connected to harness.	Code changes from FMI 4 to FMI 3.	OK - The diagnostic changed to FMI 3 when the sensor was disconnected. Repair: Replace the sensor. Note: To assure sensor replacement has corrected the problem, use Cat ET to check for the presence of the faulty code. STOP NOT OK - The FMI 4 diagnostic code remains active when sensor is disconnected. The sensor not the cause of the problem. Proceed to Test Step 6.
6. Check The Signal Circuit For A Short To Ground A. Turn the key start switch and the disconnect switch OFF. B. Disconnect the J1 and J2 harness connectors from the ECM. C. Measure the resistance between the signal contact for sensor and all other contacts used in the J1 and J2 harness connectors.	The resistance is greater than 5K Ω.	OK - The resistance is greater than 5K Ω. The harness circuit is correct. Proceed to Test Step 7. NOT OK - The resistance is less than 5 Ω. A short circuit exists between frame ground and the signal circuit. 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. STOP
7. Check If The Diagnostic Code Remains A. Turn the key start switch and the disconnect switch ON. B. Clear all diagnostic codes. C. Operate the machine. D. Stop machine and engage the safety lock lever. E. Check if the diagnostic code for the sensor is active.	The code for the sensor is NO longer present.	OK - The diagnostic code does not exist at this time. The initial diagnostic code may have been caused by a poor electrical connection or a short at one of the harness connections. Resume machine operation. STOP NOT OK - The diagnostic trouble code has not been corrected. Repair: Recheck the circuit and perform this procedure again. If the diagnostic code is still active, 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 greatly reduce repair time. Follow the procedure in Troubleshooting , "ECM - Replace" to replace the ECM. STOP