P21C4

P21C4-(DIESEL EXHAUST FLUID) REDUCTANT LINE HEATER RELAY CONTROL CIRCUIT HIGH




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

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 Powertrain Control Module (PCM) immediately after the diagnostics runs and fails. 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.

- Set Condition:
The DEF Dosing Control Unit detects that the DEF Line Heater Relay Control 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.
2. 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 DEF LINE HEATER RELAY
1. With the scan tool, Erase DTCs.
2. Turn the ignition off.
3. Replace the DEF Line Heater Relay with a known good relay.
4. Turn the ignition on.
5. With the scan tool, navigate to Actuator Tests and actuate the Line Heater Relay.
6. With the scan tool, View DTCs.

Did the DTC return?

Yes

- Go To 3

No

- Repair complete.
- Perform the POWERTRAIN VERIFICATION TEST - 6.7L. Powertrain Verification Test.

3. CHECK FOR THE (K475) DEF LINE HEATER RELAY SIGNAL CIRCUIT SHORTED TO ANOTHER CIRCUIT




1. Stop actuation of the Line Heater Relay.
2. Turn the ignition off.
3. Remove the DEF Line Heater Relay.
4. Disconnect the DEF Dosing Control Unit C2 harness connector.
5. Measure the resistance between the (K475) DEF Line Heater Relay Signal circuit and all other circuits in the DEF Dosing Control Unit C2 harness connector.

Is the resistance above 10k Ohms between the (K475) DEF Line Heater Relay Signal circuit and all other circuits?

Yes

- Go To 4

No

- Repair the (K475) DEF Line Heater Relay Signal circuit for a short to the circuit that measured below 10k Ohms.
- Perform the POWERTRAIN VERIFICATION TEST - 6.7L. Powertrain Verification Test.

4. CHECK FOR THE (K429) DEF LINE HEATER RELAY CONTROL CIRCUIT SHORTED TO ANOTHER CIRCUIT




1. Measure the resistance between the (K429) DEF Line Heater Relay Control circuit and all other circuits in the DEF Dosing Control Unit C2 harness connector.

Is the resistance above 10k Ohms between the (K429) DEF Line Heater Relay Control 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 (K429) DEF Line Heater Relay Control circuit for a short to the circuit that measured below 10k Ohms.
- Perform the POWERTRAIN VERIFICATION TEST - 6.7L. Powertrain Verification Test.