C175-20 Locomotive Engine Caterpillar

Use this procedure to troubleshoot a problem with the DEF tank sensor. Also, use this procedure if one of the following diagnostic codes is active or easily repeated.

Table 1

J1939 Code and Description	CDL Code and Description	Comments
4367-3 Aftertreatment #1 DEF Quick Thaw Tank Level : Voltage Above Normal	3131-3 Aftertreatment #1 DEF Tank #2 Level Sensor : Voltage Above Normal	The Electronic Control Module (ECM) detects signal voltage that is not in the acceptable range. The code is logged.
4367-4 Aftertreatment #1 DEF Quick Thaw Tank Level : Voltage Below Normal	3131-4 Aftertreatment #1 DEF Tank #2 Level Sensor : Voltage Below Normal	The ECM detects signal voltage that is not in the acceptable range. The code is logged.
4368-3 Aftertreatment #1 DEF Tank #2 Temperature : Voltage Above Normal	3135-3 Aftertreatment #1 DEF Tank #2 Temperature Sensor : Voltage Above Normal	The ECM detects signal voltage that is not in the acceptable range. The code is logged.
4368-4 Aftertreatment #1 DEF Tank #2 Temperature : Voltage Below Normal	3135-4 Aftertreatment #1 DEF Tank #2 Temperature Sensor : Voltage Below Normal	The ECM detects signal voltage that is not in the acceptable range. The code is logged.

The signal for the Diesel Exhaust Fluid (DEF) tank level sensor is routed to terminal 1 of the tank header unit. The signal for the DEF tank temperature sensor is routed to terminal 3 of the tank header unit. The sensor return is shared and is routed to terminal 2 of the tank header unit. The Electronic Control Module (ECM) provides short circuit protection for the internal power supply. A short circuit to the battery will not damage the internal power supply.

Illustration 1	g01240891
(1) DEF level sensor signal (2) Sensor return (3) DEF tank temperature signal

Illustration 2	g06136353

Table 2

Troubleshooting Test Steps	Values	Results
1. Check for Codes A. Apply electrical power to the engine. B. Connect Cat® Electronic Technician (ET) to the service tool connector. C. Determine if a code is active or logged.	Codes	Result: A -3 code is active. Proceed to Test Step 2. Result: A -4 code is active. Proceed to Test Step 3.
2. Create a Short at the Sensor Connector A. Verify that the wiring harness connector is free of debris, free of corrosion and securely connected. B. Install a jumper wire between the appropriate signal and return wire at the sensor connector to create a short. C. Apply electrical power to the engine. D. Connect Cat ET. E. Use Cat ET to monitor the following codes: - -4 code F. Remove electrical power from the engine.	Create a Short	Result: A -4 code becomes active. Repair: The wiring is OK. Replace the DEF tank header assembly. Verify that the repair eliminated the problem. Result: A -4 code does not become active. Repair: Repair or replace the wiring harness. Verify that the repair eliminated the problem.
3. Create an Open at the Sensor Connector A. Disconnect the connector of the tank header unit. B. Apply electrical power to the engine. C. Connect Cat ET. D. Use Cat ET to monitor the following codes: - -3 code D. Remove electrical power from the engine.	Create an Open	Result: A -3 code becomes active. Repair: The wiring is OK. Replace the DEF tank header assembly. Verify that the repair eliminated the problem. Result: A -3 code does not become active. Repair: Repair or replace the wiring harness. Verify that the repair eliminated the problem.

If the procedure did not correct the issue, contact your Cat dealer Technical Communicator (TC). For further assistance, your TC can confer with the Dealer Solutions Network (DSN).