924K, 926M, 930K, 930M, 938K and 938M Wheel Loaders Caterpillar

Sensor Signal (Analog, Passive) - Test

Usage:

930K FRK

Machine ECM

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

Show/hide table

Table 1
Machine ECM (MID 39)
DTC	Code Description	System Response
96-3	Fuel Level Sensor: Voltage Above Normal	Fuel level gauge will be unavailable.
96-4	Fuel Level Sensor: Voltage Below Normal	Fuel level gauge will be unavailable.
177-3	Transmission Oil Temperature Sensor: Voltage Above Normal	ECM will assume that the transmission fluid is low and shifts will be harsh Machine maximum speed will be limited to 75% of range four runout.
177-4	Transmission Oil Temperature Sensor: Voltage Below Normal	ECM will assume that the transmission fluid is low and shifts will be harsh Machine maximum speed will be limited to 75% of range four runout.
779-3	Cab Air Temperature Sensor: Voltage Above Normal	A level 1 diagnostic code will be generated.
779-4	Cab Air Temperature Sensor : Voltage Below Normal	A level 1 diagnostic code will be generated.
2357-3	Air Conditioner Evaporator Coil Temperature Sensor: Voltage Above Normal	The air conditioning system will not work properly.
2357-4	Air Conditioner Evaporator Coil Temperature Sensor: Voltage Below Normal	The air conditioning system will not work properly.
2663-3	Cab Ventilation Duct Temperature Sensor: Voltage Above Normal	A level 1 diagnostic code will be generated.
2663-4	Cab Ventilation Duct Temperature Sensor: Voltage Below Normal	A level 1 diagnostic code will be generated.

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. This condition 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.

Show/hide table




Illustration 1	g03750779
Schematic of the passive analog sensors

Note: The diagram above is a simplified schematic of the connections for the passive analog connections. The schematic is electrically correct. However, not all of the possible harness connectors are shown. Refer to the latest revision of the electrical schematic for the specific machine being serviced for the complete schematic.

The table below is a reference that can be used when checking the resistance of the temperature sensors listed in the table above.

Show/hide table

Table 2
CELSIUS TEMPERATURE	FAHRENHEIT TEMPERATURE	RESISTANCE
10	50	1991.4
15	59	1571.9
20	68	1249.5
25	77	1000
30	86	805.5

Diagnostic Trouble Code Procedure

Note: Prior to beginning this procedure, inspect the harness connectors that are involved in this 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. Check the wiring for pinch points or abrasions. Look for and repair areas that indicate wires are exposed. If a problem with a connection is found, correct the problem and verify that this diagnostic code is active before performing a troubleshooting procedure.

Show/hide table

Table 3
Troubleshooting Test Steps	Values	Results
1. Identify The Active DTC Code Associated With The Suspect Circuit	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 Sensor Note: See Table 2 for a list of resistances related to specific temperature values. The maximum resistance for the sensor is 33,650 Ω, the minimum is 51.2 Ω. 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 Table 2.	OK - The resistance reading agrees with the values in 2. Proceed to Test Step 3. NOT OK - The resistance reading does not agree with the values in 2. Repair: Replace the sensor. Proceed to Test Step 7.
3. 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. Disconnect the J1 and J2 connectors from the ECM. D. At the harness connector for the sensor install a jumper wire. E. At the harness connector for the ECM measure the resistance at the contacts for the sensor.	The resistance reading is less than 5 Ω.	OK - The resistance is less than 5 Ω. Proceed to Test Step 4. NOT OK - The resistance is greater than 5 Ω. Repair: Either the signal or the return circuit wire is open. Repair or replace the harness. Proceed to Test Step 7.
4. Check The Signal Circuit For A Short. A. The disconnect switch and the key start switch remain in the OFF position. B. The harness connectors J1 and J2 remain disconnected from the ECM. C. Remove the jumper wire that was installed during the previous Test Step. D. At the ECM harness connectors measure the resistance between the positive connector and all J1 and J2 contacts.	Each resistance reading is greater than 5000 Ω.	OK - Each measurement is greater than 5000 Ω. Proceed to Test Step 7. NOT OK - A resistance measurement is less than 5000 Ω. Repair: A short exists between the signal circuit and the circuit with the low resistance measurement. Repair or replace the machine harness. Proceed to Test Step 7.
Begin Process For FMI 4 Troubleshooting HERE
5. Check The Sensor A. Turn key start switch and disconnect switch ON. B. Ensure that the diagnostic code is active. C. Disconnect sensor from machine harness.	DTC is active.	OK - Diagnostic code remains active. Proceed to Test Step 6. NOT OK - Diagnostic code is no longer active. Repair: Replace the sensor. After sensor replacement, confirm code is not active. Proceed to Test Step 7.
6. 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 machine harness connection at sensor. C. Disconnect machine harness connections at switch panel. D. At the machine harness connector for the switch panel, measure resistance from the signal contact of machine harness to all possible sources of ground. Measure resistance to all contacts of machine harness connectors for the monitor.	Each reading greater than 5K Ω.	OK - All resistance readings are greater than 5K Ω. Proceed to Test Step 7. NOT OK - One or more of the readings are less than 5 Ω. Repair: A short exists between the signal contact and the circuit with the low resistance. 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 7.
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 the machine and engage safety lock lever. E. Check if diagnostic code for the sensor is active.	DTC Code is no longer active.	OK - Diagnostic code does not exist at this time. Initial diagnostic code may have been caused by poor electrical connection or short at one of the harness connections. Resume machine operation. Repair: The initial diagnostic code was probably caused by a poor electrical connection or a short at one of the harness connectors. Resume normal machine operation. NOT OK - Diagnostic trouble code has not been corrected. Repair: If the diagnostic code has not been corrected after performing the procedure a second time, follow the procedure below for replacing the ECM. 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. If the ECM requires replacement, see Troubleshooting, "ECM - Replace". STOP