P0031

P0031-O2 SENSOR 1/1 HEATER CIRCUIT LOW

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

Theory of Operation
For the wideband 02 sensor to deliver accurate readings the sensing elements must be heated. A Positive Temperature Coefficient (PTC) element inside the O2 sensor heats up as current passes through it. The Powertrain Control Module (PCM) turns on this circuit based on Engine Coolant Temperature (ECT) and engine loads. The PCM monitors the O2 sensors heaters for proper operation. If a malfunction happens the circuit is shut off and a DTC set.
- When Monitored:
Continuously during O2 heater operation with battery voltage between 10.4 and 15.75 Volts.

- Set Condition:
The Powertrain Control Module (PCM) detects that the O2 sensor heater element input is below the minimum acceptable voltage. One trip fault. Three good trips to turn off the MIL.





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

1. ACTIVE DIAGNOSTIC TROUBLE CODE (DTC)
1. Start the engine and allow it to idle for at least 60 seconds.

WARNING: When the engine is operating, do not stand in direct line with the fan. Do not put your hands near the pulleys, belts or fan. Do not wear loose clothing. Failure to follow these instructions may result in possible serious or fatal injury.

2. With the scan tool, select View DTCs.

Is the DTC Active at this time?

Yes

- Go To 2

No

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

2. O2 HEATER ELEMENT
1. Turn the ignition off.

NOTE: Allow the O2 Sensor to cool down to room temperature.

2. Disconnect the 1/1 O2 Sensor harness connector.
3. Measure the resistance across the O2 Sensor Heater element, between the Heater Control terminal and the Heater ground terminal at the component.

NOTE: O2 Heater Element resistance values should be measured at 21.1° C (70° F). The resistance value will vary with different temperature values.

Is the O2 Sensor Heater Element resistance between 2.0 and 30.0 Ohms?

Yes

- Go To 3

No

- Verify that there is good pin to terminal contact in the 1/1 O2 Sensor and Powertrain Control Module connectors. If OK, replace the 1/1 O2 Sensor. Oxygen Sensor - Removal.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.

3. O2 1/1 HEATER CONTROL CIRCUIT SHORTED TO GROUND
1. Disconnect the PCM C1 harness connector.
2. Measure the resistance between ground and the O2 1/1 Heater Control circuit in the O2 Sensor harness connector.

Is the resistance below 5.0 Ohms?

Yes

- Repair the short to ground in the O2 1/1 Heater Control circuit.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.

No

- Go To 4

4. O2 1/1 HEATER CONTROL CIRCUIT OPEN
1. Measure the resistance of the O2 1/1 Heater Control circuit between the 1/1 Oxygen Sensor harness connector and the PCM C1 harness connector.

Is the resistance below 0.5 of an Ohm?

Yes

- Go To 6

No

- Repair the open in the O2 1/1 Heater Control circuit.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.

5. EXCESSIVE RESISTANCE IN THE ASD RELAY O2 1/1 HEATER FEED CIRCUIT
1. Measure the resistance of the ASD Relay O2 1/1 Heater Feed circuit between the 1/1 Oxygen Sensor harness connector and the ASD Relay Output terminal.

Is the resistance below 0.5 of an Ohm?

Yes

- Go To 6

No

- Repair the excessive resistance in the ASD Relay O2 1/1 Heater Feed circuit.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.

6. POWERTRAIN CONTROL MODULE (PCM)
1. Using the wiring diagram/schematic as a guide, inspect the wiring and connectors between the Oxygen Sensor 1/1 and the Powertrain Control Module (PCM).
2. Look for any chafed, pierced, pinched or partially broken wires.
3. Look for broken, bent, pushed out or corroded terminals. Verify that there is good pin to terminal contact in the 1/1 O2 Sensor and Powertrain Control Module connectors.
4. Perform any Technical Service Bulletins that may apply.

Were there any problems found?

Yes

- Repair as necessary.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.

No

- Replace and program the Powertrain Control Module. PCM/ECM Reprogramming.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.