C7.1 Engines Caterpillar

The Dosing Control Unit (DCU) monitors the voltage and current flow to the Diesel Exhaust Fluid (DEF) line heater relay and the heated DEF lines. Refer to Table 1. Faults are notified to the engine Electronic Control Module (ECM) over the J1939 data bus.

The engine ECM sets a diagnostic trouble code if the current flow through a circuit is incorrect. A -5 code indicates that the current flow through the circuit is low and there is an open circuit. A -6 code indicates that the current flow through the circuit is high and there is a short in the circuit.

Table 1 lists the diagnostic codes for incorrect current flow.

Table 1

Diagnostic Trouble Codes for the DEF Line Heaters
J1939 Code	CDL Code	Code Description	Comments
4354-5	3110-5	Aftertreatment #1 SCR Catalyst Reagent Line Heater #1 : Current Below Normal	This code indicates that there is a fault in the #1 line heater circuit that is probably an open circuit. The #1 line heater is in the return line.
4354-6	3110-6	Aftertreatment #1 SCR Catalyst Reagent Line Heater #1 : Current Above Normal	This code indicates that there is a fault in the #1 line heater circuit that is probably a short circuit. The #1 line heater is in the return line.
4354-12	3110-12	Aftertreatment #1 SCR Catalyst Reagent Line Heater #1 : Failure	This code indicates that there is a fault in the #1 line heater circuit. The #1 line heater is in the return line.
4355-5	3111-5	Aftertreatment #1 SCR Catalyst Reagent Line Heater #2 : Current Below Normal	This code indicates that there is a fault in the #2 line heater circuit that is probably an open circuit. The #2 line heater is in the pressure line to the DEF injector.
4355-6	3111-6	Aftertreatment #1 SCR Catalyst Reagent Line Heater #2 : Current Above Normal	This code indicates that there is a fault in the #2 line heater circuit that is probably a short circuit. The #2 line heater is in the pressure line to the DEF injector.
4356-5	3112-5	Aftertreatment #1 SCR Catalyst Reagent Line Heater #3 : Current Below Normal	This code indicates that there is a fault in the #3 line heater circuit that is probably an open circuit. The #3 line heater is in the suction line.
4356-6	3112-6	Aftertreatment #1 SCR Catalyst Reagent Line Heater #3 : Current Above Normal	This code indicates that there is a fault in the #3 line heater circuit that is probably a short circuit. The #3 line heater is in the suction line.
5491-5	3822-5	Aftertreatment 1 Diesel Exhaust Fluid Line Heater Relay: Current Below Normal	This code indicates that there is a fault in the line heater relay circuit that is probably an open circuit.
5491-6	3822-6	Aftertreatment 1 Diesel Exhaust Fluid Line Heater Relay: Current Above Normal	This code indicates that there is a fault in the line heater relay circuit that is probably a short circuit.
Follow the troubleshooting procedure to identify the root cause of the fault.

Note: Refer to Troubleshooting, "Sensors and Electrical Connectors"for the locations of the components listed in this procedure.

Illustration 1	g06006320
Schematic diagram of the DEF heater circuit

Illustration 2	g03126456
View of the pin locations for the DEF line heaters on the 86-pin (C1) connector (1) DEF pressure line heater #2 return (2) DEF return line heater #1 return (48) DEF suction line heater #3 return

Illustration 3	g03126936
View of the pin locations for the DEF line heaters on the 53-pin (C2) connector (30) DEF line heater relay supply (41) DEF line heater relay return

Illustration 4	g03808796
DEF heater relay socket (1) Battery supply (2) Relay coil supply (4) DEF line heater supply (5) Relay coil return

Illustration 5	g03128456
Heated DEF line connector (1) Battery + (2) Return

Complete the procedure in the order in which the steps are listed.

Table 2

Troubleshooting Test Steps	Values	Results
1. Inspect Electrical Connectors and Wiring A. Turn the keyswitch to the OFF position. B. Inspect the C1 and C2 connectors. C. Inspect the connectors for the DEF line heaters and the DEF line heater relay. D. Perform a 45 N (10 lb) pull test on each of the wires in the DCU connector, the line heaters, and the line heater relay. E. Check all the wiring associated with the DEF line heaters for abrasions and pinch points.	Damaged wire or connector	Result: A damaged wire or damaged connector was not found. Proceed to Test Step 2. Result: A damaged wire or damaged connector was found. Repair: Repair the damaged wire or the damaged connector. Use the electronic service tool to clear all logged diagnostic codes. Proceed to Test Step 14.
2. Determine the Diagnostic Code A. Establish communication between the electronic service tool and the engine ECM. If necessary, refer to Troubleshooting, "Electronic Service Tools". B. Download the "Warranty Report" from the engine ECM before troubleshooting or clearing diagnostic trouble codes. C. Establish communication between the electronic service tool and the DCU. D. Look for one of the codes that are listed in Table 1.	Diagnostic Trouble Codes	Result: There is an active or logged 5491-5 or 3822-5 code. Proceed to Test Step 3. Result: There is an active or logged 5491-6 or 3822-6 code. Proceed to Test Step 5. Result: There is an active or logged 435x -5 or 311x-5 code. Proceed to Test Step 7. Result: There is an active or logged 435x-6 or 311x-6 code. Proceed to Test Step 12.
3. Create a Short Circuit at the Relay Connector A. Turn the keyswitch to the OFF position. Allow 2 minutes to elapse. B. Disconnect the connector for the DEF line heater relay. C. Fabricate a jumper wire and install the jumper wire between terminal 2 and terminal 5 on the harness connector for the relay. D. Turn the keyswitch to the ON position. E. Monitor the active diagnostic codes on the electronic service tool. Check for a 5491-6 or 3822-6 diagnostic code. Wait at least 30 seconds in order for the diagnostic codes to become active. F. Turn the keyswitch to the OFF position.	Short circuit recognized	Result: The 5491-5 or 3822-5 diagnostic code remains active with the jumper installed. Remove the jumper wire and proceed to Test Step 4. Result: A 5491-6 or 3822-6 diagnostic code is active with the jumper installed. Repair: Replace the DEF line heater relay. Proceed to Test Step 14.
4. Check the Relay Wiring for an Open Circuit A. Disconnect the C2 connector from the DCU. B. Use a suitable multimeter to measure the resistance between the following points: 1. C2:30 and terminal 2 on the harness connector for the relay. 2. C2:41 and terminal 5 on the harness connector for the relay.	Less than 2.0 Ohms	Result: At least one of the resistance measurements is greater than 2.0 Ohms. Repair: Replace the wiring between the DEF line heater relay and the C2 connector on the DCU. Proceed to Test Step 14. Result: Both resistance measurements are less than 2.0 Ohms. Repair: Reconnect the relay connector and the C2 connector. Turn the keyswitch to the ON position. If the fault is still present, contact the Dealer Solutions Network (DSN).
5. Create an Open Circuit at the Relay Connector A. Turn the keyswitch to the OFF position. B. Disconnect the connector for the DEF line heater relay. C. Turn the keyswitch to the ON position. D. Monitor the active diagnostic codes on the electronic service tool. Check for a 5491-5 or 3822-5 diagnostic code. Wait at least 30 seconds in order for the diagnostic codes to become active. E. Turn the keyswitch to the OFF position.	Open circuit recognized	Result: The 5491-6 or 3822-6 diagnostic code remains active with the relay disconnected. Proceed to Test Step 6. Result: A 5491-5 or 3822-5 diagnostic code is active with the relay disconnected. Repair: Replace the DEF line heater relay. Proceed to Test Step 14.
6. Check the Relay Wiring for a Short Circuit A. Turn the keyswitch to the OFF position. B. Disconnect the C2 connector from the DCU. C. Use a suitable multimeter to take the following resistance measurements: C2:30 (harness side) to all other pins on the C2 harness connector. C2:41 (harness side) to all other pins on the C2 harness connector.	Greater than 100 Ohms	Result: At least one of the resistance measurements is less than 100 Ohms. Repair: Replace the wiring between the DEF line heater relay and the C2 connector on the DCU. Proceed to Test Step 14. Result: All resistance measurements are greater than 100 Ohms. Reconnect the relay connector and the C2 connector. Turn the keyswitch to the ON position. If the fault is still present, contact the Dealer Solutions Network (DSN).
7. Check for Power at DEF Line Heater Relay A. Turn the keyswitch to the OFF position for 2 minutes. The keyswitch must be off for 2 minutes to allow the DEF pump to purge, reset the code, and reset the DCU. B. Remove the DEF line heater relay from the harness. C. Verify that the harness connector is free of debris and free of corrosion. D. Turn the keyswitch to the ON position. E. Check for battery voltage between terminal 1 of the heated line relay socket and a known good ground.	Battery voltage	Result: The voltage between terminal 1 and a good ground source is equal to battery voltage. Turn the keyswitch to the OFF position for 2 minutes. Proceed to Test Step 8. Result: The voltage between terminal 1 and a good ground source is not equal to battery voltage. Repair: Refer to the electrical schematic and troubleshoot the power source from the VLPM.
8. Bypass the DEF Line Heater Relay A. Fabricate a jumper wire and install the jumper wire between terminal 1 and terminal 4 on the harness connector for the relay. B. Turn the keyswitch to the ON position. C. Monitor the active diagnostic codes on the electronic service tool. Check for a 435X-5 or 311X-5 diagnostic code. Wait at least 30 seconds in order for the diagnostic codes to become active. D. Turn the keyswitch to the OFF position.	Diagnostic codes	Result: The 435X-5 or 311X-5 diagnostic code is no longer active. Repair: Replace the DEF line heater relay. Proceed to Test Step 14. Result: The 435X-5 diagnostic code is still active. Repair: Remove the jumper wire and reconnect the relay. Proceed to Test Step 9.
9. Check for Battery Voltage at the Line Heater Connector A. Turn the keyswitch to the OFF position for 2 minutes. The keyswitch must be off for 2 minutes to allow the DEF pump to purge, reset the code, and reset the DCU. B. Disconnect the connector for the DEF line heater with active 435X-5 or 311X-5 diagnostic code. C. Verify that the harness connector is free of debris and free of corrosion. D. Turn the keyswitch to the ON position. E. Use the electronic service tool to perform the "DEF Heated Lines Test". F. Use a suitable multimeter to measure the voltage between terminal 1 on the harness connector for the suspect line heater and a suitable ground. G. Use the electronic service tool to stop the "DEF Heated Lines Test". H. Turn the keyswitch to the OFF position.	Battery voltage	Result: The voltage between terminal 1 and a good ground source is equal to battery voltage. Proceed to Test Step 10. Result: The voltage between terminal 1 and a good ground source is not equal to battery voltage. Repair: Replace the wiring between the DEF line heater relay and the suspect DEF line heater. Proceed to Test Step 14.
10. Create a Short Circuit at the DEF Line Heater Connector A. Fabricate a jumper wire. Install the jumper wire between terminal 1 and terminal 2 on the harness connector for the suspect line heater. B. Turn the keyswitch to the ON position. C. Monitor the active diagnostic codes on the electronic service tool. Check for a 435X-6 or 311X-6 diagnostic code. Wait at least 30 seconds in order for the diagnostic codes to become active. D. Turn the keyswitch to the OFF position.	Diagnostic codes	Result: The 435X-5 or 311X-5 diagnostic code is still active with the jumper installed. Remove the jumper and proceed to Test Step 11. Result: A 435X-6 or 311X-6 diagnostic code is active with the jumper installed. Repair: Replace the suspect DEF line heater. Proceed to Test Step 14.
11. Check the Wiring for an Open Circuit A. Disconnect the C1 connector from the DCU. B. Check the resistance between terminal 2 on the harness connector for the suspect DEF line heater and the appropriate terminal on the C1 connector (harness side). Refer to Illustration 2.	Less than 2.0 Ohms	Result: The measured resistance is less than 2.0 Ohms. Contact the Dealer Solutions Network (DSN). Result: The measured resistance is more than 2.0 Ohms. Repair: Replace the wiring between the suspect DEF line heater and the C1 connector on the DCU. Proceed to Test Step 14.
12. Create an Open Circuit at the DEF Line Heater Connector A. Turn the keyswitch to the OFF position for 2 minutes. The keyswitch must be off for 2 minutes to allow the DEF pump to purge, reset the code, and reset the DCU. B. Disconnect the connector for the DEF line heater with the 435X-6 or 311X-6 diagnostic code. C. Turn the keyswitch to the ON position. D. Use the electronic service tool to perform the "DEF Heated Lines Test". E. Monitor the active diagnostic codes on the electronic service tool. Check for a 435X-5 or 311X-5 diagnostic code. Wait at least 30 seconds in order for the diagnostic codes to become active. F. Use the electronic service tool to stop the "DEF Heated Lines Test". G. Turn the keyswitch to the OFF position.	Diagnostic codes	Result: The 435X-6 or 311X-6 diagnostic code is still active with the line heater disconnected. Proceed to Test Step 13. Result: A 435X-5 or 311X-5 diagnostic code is active with the line heater disconnected. Repair: Replace the suspect line heater. Proceed to Test Step 14.
13. Check the Heater Wiring for a Short Circuit A. Turn the keyswitch to the OFF position. B. Disconnect the C1 connector from the DCU. C. Verify that the harness connector is free of debris and free of corrosion. D. Measure the resistance between the suspect heater return terminal on the C1 harness connector and all other terminals on the C1 harness connector.	Greater than 100 Ohms	Result: All resistance measurements are greater than 100 Ohms. Contact the Dealer Solutions Network (DSN). Once any recommended repairs have been completed, proceed to Test Step 14. Result: At least one of the resistance measurements is less than 100 Ohms. Repair: Replace the wiring between the suspect DEF line heater and the DCU. Proceed to Test Step 14.
14. Perform a "DEF Heated Line Test" A. Establish communication between the electronic service tool and "Diesel Exhaust Fluid Controller #1". If necessary, refer to Troubleshooting, "Electronic Service Tools". B. Use the electronic service tool to perform a "DEF Heated Line - Test".	Test passed	Result: The test passed and no diagnostic codes became active. Return the engine to service. Result: The test failed. Repair: Troubleshoot any diagnostic codes that became active during the test. Refer to Troubleshooting"Diagnostic Trouble Codes". If the fault is still present, contact the Dealer Solutions Network (DSN).