P20BD

P20BD-(DIESEL EXHAUST FLUID) REDUCTANT PRESSURE LINE HEATER CONTROL CIRCUIT/OPEN

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

This DTC referring to the DEF Pressure 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. 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:
When line heating is commanded on.

- Set Condition:
The DEF Dosing Control Unit detects that the DEF Pressure Line heater circuit is open or shorted to ground.

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. CHECK FOR RELATED DTCs
1. Turn the ignition on.
2. With the scan tool, View all active DTCs.

Are the P20BD, P20B9 and P20C1 DTCs active together?

Yes

- Go To 2

No

- Go To 4

2. CHECK THE (K476) DEF LINE HEATER OUTPUT CIRCUIT FOR AN OPEN/HIGH RESISTANCE

1. Turn the ignition off.
2. Remove the DEF Line Heater Relay.
3. Disconnect the DEF Pressure Line Heater harness connector.
4. Measure the resistance of the (K476) DEF Line Heater Output circuit between terminal 87 of the Line Heater Relay connector and the DEF Pressure Line Heater harness connector.

Is the resistance below 5.0 Ohms?

Yes

- Go To 3

No

- Repair the (K476) DEF Line Heater Relay Output circuit for an open or high resistance. If the circuit fuse is found to be open, check the (K476) DEF Line Heater Relay Output circuit for a short to ground.
- Perform the POWERTRAIN VERIFICATION TEST - 6.7L. Powertrain Verification Test.

3. CHECK THE DEF LINE HEATER
1. Reconnect the DEF Pressure Line Heater harness connector.
2. Replace the DEF Line Heater Relay with a known good relay.
3. Turn the ignition on.
4. With the scan tool, Erase DTCs.
5. With the scan tool, navigate to Systems Tests and actuate the DEF Pressure Line Heater.
6. With the scan tool, View all active DTCs.

Did the DTCs return?

Yes

- Using the wiring diagram as a guide, check the DEF Line Heater Relay control circuits for an open or short to ground.
- Perform the POWERTRAIN VERIFICATION TEST - 6.7L. Powertrain Verification Test.

No

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

4. CHECK THE (K476) DEF LINE HEATER OUTPUT CIRCUIT FOR AN OPEN/HIGH RESISTANCE

1. Disconnect the DEF Dosing Control Unit C1 harness connector.
2. Measure the resistance of the (K478) DEF Pressure Line Heater Return circuit between the DEF Pressure Line Heater harness connector and the DEF Dosing Control Unit C1 harness connector.

Is the resistance below 5.0 Ohms?

Yes

- Go To 6

No

- Repair the (K478) DEF Pressure Line Heater Return circuit for an open or high resistance.
- Perform the POWERTRAIN VERIFICATION TEST - 6.7L. Powertrain Verification Test.

6. CHECK THE (K478) DEF PRESSURE LINE HEATER RETURN CIRCUIT FOR A SHORT TO GROUND

1. Measure the resistance between ground and the (K478) DEF Pressure Line Heater Return circuit at the DEF Pressure Line Heater harness connector.

Is the resistance above 10k Ohms?

Yes

- Go To 7

No

- Repair the (K478) DEF Pressure Line Heater Return circuit for a short to ground.
- Perform the POWERTRAIN VERIFICATION TEST - 6.7L. Powertrain Verification Test.

7. CHECK THE RESISTANCE OF THE DEF PRESSURE LINE HEATER
1. Measure the resistance across the terminals of the DEF Pressure Line Heater.

Does the resistance measure between 5.7 Ohms and 6.9 Ohms?

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

- Replace the DEF Pressure Line. Diesel Exhaust Fluid Pressure Line - Removal.
- Perform the POWERTRAIN VERIFICATION TEST - 6.7L. Powertrain Verification Test.