P0031

P0031-O2 SENSOR 1/1 HEATER CIRCUIT LOW




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

The engine aftertreatment system monitors the O2 Sensor content in the diesel engine exhaust. The Engine Control Module (ECM) monitors the exhaust gases for oxygen content and varies the rich/lean fuel mixture of the intake air fuel mixture to adjust the system. This diagnostic monitors the status message broadcast by the Smart O2 Sensor Module for the Upstream O2 Sensors internal heater circuit. The ECM will set the fault if it receives a FMI (Failure Mode Indicator) message from the Smart O2 Module. The ECM will illuminate the MIL lamp immediately when the diagnostic runs and fails. The ECM will turn off the MIL lamp diagnostic runs and passes in four consecutive drive cycles.

- When Monitored:
This diagnostic runs when the engine is running.

- Set Condition:
The Engine Control Module (ECM) will set the fault if it receives a FMI (Failure Mode Indicator) message from the Smart O2 Module.





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

NOTE: Before replacing any O2 Sensor or O2 Sensor Module, check aftertreatment wiring harness for spread terminals. For wiring harness checking procedure, DO NOT back probe, use Miller Tool Kit 8197A (6801 Tool).

1. ACTIVE DTC
1. Turn the ignition on.
2. With the scan tool, record all Freeze frame data.
3. With the scan tool, erase DTCs.
4. Turn the ignition off for 30 seconds.
5. Start the engine and let idle for up to five minutes.
6. With the scan tool, read DTCs.

Did the DTC reset?

Yes

- Go To 2

No

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

2. (K79) O2 SENSOR 1/1 HEATER RETURN CIRCUIT SHORTED TO VOLTAGE




1. Turn the engine off.
2. Disconnect the Smart O2 Sensor Module harness connector.
3. Turn the ignition on.
4. Measure the voltage on the (K79) O2 Sensor 1/1 Heater Return circuit at the Smart O2 Sensor Module harness connector.

Is there any voltage present?

Yes

- Repair the short to voltage on the (K79) O2 Sensor 1/1 Heater Return circuit.
- Perform the POWERTRAIN VERIFICATION TEST - 6.7L. Powertrain Verification Test.

No

- Go To 3

3. (K79) O2 SENSOR 1/1 HEATER RETURN CIRCUIT SHORTED TO GROUND




1. Turn the ignition off.
2. Disconnect the O2 Sensor 1/1 harness connector.
3. Measure the resistance between ground and the (K79) O2 Sensor 1/1 Heater Return circuit at the O2 Sensor 1/1 harness connector.

Is the resistance below 10k Ohms?

Yes

- Repair the short to ground in the (K79) O2 Sensor 1/1 Heater Return circuit.
- Perform the POWERTRAIN VERIFICATION TEST - 6.7L. Powertrain Verification Test.

No

- Go To 4

4. (K99) O2 SENSOR 1/1 HEATER SUPPLY CIRCUIT SHORTED TO GROUND




1. Measure the resistance between ground and the (K99) O2 Sensor 1/1 Heater Supply circuit at the O2 Sensor 1/1 harness connector.

Is the resistance below 10k Ohms?

Yes

- Repair the short to ground in the (K99) O2 Sensor 1/1 Heater Supply circuit.
- Perform the POWERTRAIN VERIFICATION TEST - 6.7L. Powertrain Verification Test.

No

- Go To 5

5. (K99) 02 SENSOR 1/1 HEATER SUPPLY CIRCUIT OPEN




1. Measure the resistance of the (K99) O2 Sensor 1/1 Heater Supply circuit between the O2 Sensor 1/1 harness connector and the Smart O2 Sensor Module harness connector.

Is the resistance below 10.0 Ohms?

Yes

- Go To 6

No

- Repair the open or high resistance in the (K99) O2 Sensor 1/1 Heater Supply circuit.
- Perform the POWERTRAIN VERIFICATION TEST - 6.7L. Powertrain Verification Test.

6. (K79) O02 1/1 HEATER RETURN CIRCUIT OPEN




1. Measure the resistance of the (K79) O2 Sensor 1/1 Heater Return circuit between the O2 Sensor 1/1 harness connector and the Smart O2 Sensor Module harness connector.

Is the resistance below 10.0 Ohms?

Yes

- Go To 7

No

- Repair the open or high resistance in the (K79) O2 Sensor 1/1 Heater Return circuit.
- Perform the POWERTRAIN VERIFICATION TEST - 6.7L. Powertrain Verification Test.

7. OXYGEN SENSOR




1. Measure the resistance of the O2 Sensor 1/1 Heater circuit in the O2 Sensor.

Is the resistance 3.2 ± 0.8 Ohms at ambient temperature?

Yes

- Go To 8

No

- Replace the O2 Sensor.
- Perform the POWERTRAIN VERIFICATION TEST - 6.7L. Powertrain Verification Test.

8. OXYGEN SENSOR AND O2 SENSOR CONTROL MODULE
1. Remove the O2 Sensor 1/1 and O2 Sensor 1/2. Clean the soot from the sensors.
2. Install the O2 Sensor 1/1 in the O2 Sensor 1/2 position.
3. Install the O2 Sensor 1/2 in the O2 Sensor 1/1 position.
4. With the scan tool, erase DTCs.
5. Turn the ignition off for 30 seconds.
6. Start the engine and let idle for two minutes.
7. With the scan tool, read DTCs.

Did the DTC change to P0037?

Yes

- Reinstall the O2 Sensor 1/2 back to it's original position and replace the O2 Sensor 1/1.
- Perform the POWERTRAIN VERIFICATION TEST - 6.7L. Powertrain Verification Test.

No

- Replace the O2 Sensor Control Module. Return the O2 Sensors back to their original positions.
- Perform the POWERTRAIN VERIFICATION TEST - 6.7L. Powertrain Verification Test.