P20C4

P20C4-(DIESEL EXHAUST FLUID) REDUCTANT RETURN LINE HEATER CONTROL CIRCUIT HIGH




For a complete wiring diagram, refer to the Wiring Information.
Theory of Operation

This DTC is referring to the DEF Supply/Purge Line Heater. Each of the Diesel Exhaust Fluid (DEF) system hoses has a built in heater to warm the fluid in the lines. The three line heaters share a common power supply via the DEF Line Heater Relay which is controlled by the DEF Dosing Control Unit. The DEF Dosing Control Unit controls the heaters individually through the line heater return circuits. The three line heater circuits are monitored at the return circuit. The DEF Dosing Control Unit will illuminate the MIL light via the PCM immediately after the diagnostics runs and fails and the line heater will be disabled. The DEF Dosing Control Unit will turn off the MIL light via the PCM when the monitor runs and passes in three consecutive key cycles.

- When Monitored:
Continuously with the ignition on, and the heater commanded on.

- Set Condition:
The DEF Dosing Control Unit detects that the DEF Purge Line Heater circuit voltage is above a calibrated value.





Always perform the Pre-Diagnostic Troubleshooting procedure before proceeding. Pre-Diagnostic Troubleshooting Procedure.

NOTE: The DEF Line Heater monitor runs only when the DEF Line Heater Relay is commanded on. If the ambient temperature is too warm for the DEF Line Heaters to be turned on, the DTC will remain active and will not be able to be erased after repair is completed. Using the scan tool, navigate to Actuator Tests and actuate the Line Heater Relay test for the appropriate Line Heater to run the diagnostic and determine if the repair has been completed. If the repair is complete, the fault will move to stored and be able to be cleared with the scan tool.

1. ACTIVE DTC
1. Turn the ignition on, engine not running.
2. With the scan tool, navigate to Systems Tests and actuate the DEF Supply and Purge Line Heaters.
3. With the scan tool, View DTCs.

Is the DTC active?

Yes

- Go To 2

No

- Perform the INTERMITTENT CONDITION - 6.7L diagnostic procedure. Intermittent Condition Test

2. CHECK THE RESISTANCE OF THE DEF SUPPLY LINE HEATER
1. Turn the ignition off.
2. Disconnect the DEF Supply/Purge Line Heater harness connector.
3. Measure the resistance across the terminals of the DEF Supply Line Heater.

Does the resistance between 7.2 Ohms and 8.6 Ohms?

Yes

- Go To 3

No

- Replace the DEF Supply/Purge Line Assembly. Diesel Exhaust Fluid Supply Line - Removal.
- Perform the POWERTRAIN VERIFICATION TEST - 6.7L. Powertrain Verification Test.

3. CHECK THE RESISTANCE OF THE DEF PURGE LINE HEATER
1. Measure the resistance across the terminals of the DEF Purge Line Heater.

Does the resistance measure between 7.4 Ohms and 8.9 Ohms?

Yes

- Go To 4

No

- Replace the DEF Supply/Purge Line Assembly. Diesel Exhaust Fluid Return Line - Removal.
- Perform the POWERTRAIN VERIFICATION TEST - 6.7L. Powertrain Verification Test.

4. CHECK THE (K480) DEF SUPPLY LINE HEATER RETURN CIRCUIT FOR A SHORT TO ANOTHER CIRCUIT




1. Disconnect the DEF Dosing Control Unit C1 harness connector.
2. Measure the resistance between the (K480) DEF Supply Line Heater Return circuit and all other circuits at the DEF Dosing Control Unit C1 harness connector

Is the resistance above 10k Ohms between the (K480) DEF Supply Line Heater Return circuit and all other circuits?

Yes

- Go To 5

No

- Repair the short between the (K480) DEF Supply Line Heater Return circuit and the circuit that measured below 10k Ohms.
- Perform the POWERTRAIN VERIFICATION TEST - 6.7L. Powertrain Verification Test.

5. CHECK THE (K479) DEF PURGE LINE HEATER RETURN CIRCUIT FOR A SHORT TO ANOTHER CIRCUIT




1. Measure the resistance between the (K479) DEF Purge Line Heater Return circuit and all other circuits at the DEF Dosing Control Unit C1 harness connector

Is the resistance above 10k Ohms between the (K479) DEF Purge Line Heater Return circuit and all other circuits?

Yes

- Replace the DEF Dosing Control Unit. Diesel Exhaust Fluid Dosing Control Unit - Removal.
- Perform the POWERTRAIN VERIFICATION TEST - 6.7L. Powertrain Verification Test.

No

- Repair the short between the (K479) DEF Purge Line Heater Return circuit and the circuit that measured below 10k Ohms.
- Perform the POWERTRAIN VERIFICATION TEST - 6.7L. Powertrain Verification Test.