Circuit Description
The DTC P0031 HO2S Heater Control Circuit Low Voltage Sensor 1 diagnostic monitors the HO2S 1 heater circuit current. The heater is powered through the ignition switch and is grounded through the PCM heater control. The PCM commands the heater ON by grounding the heater control circuit. The HO2S 1 sensor must be at operating temperature in order to accurately measure the oxygen content of the exhaust gas. The heater allows the HO2S 1 to reach operating temperature quickly.
Conditions for Running the DTC
| • | Engine running. |
| • | Intake Air Temperature (IAT) greater than -8°C (18°F). |
| • | Engine Coolant Temperature (ECT) between -8°C and +110°C (18-230°F). |
| • | Barometric pressure greater than 75 kPa. |
Conditions for Setting the DTC
| • | The heater current is less than 0.12 amps when the PCM commands the HO2S 1 heater ON. |
| • | The voltage potential between the HO2S 1 heater power and control circuits is greater than 13.99 volts when the PCM commands the heater ON. |
Action Taken When the DTC Sets
| • | The powertrain control module (PCM) illuminates the malfunction indicator lamp (MIL) after 2 consecutive ignition cycles with the fault active. |
| • | The PCM records the operating conditions at the time the diagnostic fails. This information is stored in the Freeze Frame buffer. |
Conditions for Clearing the MIL/DTC
| • | The PCM turns the MIL OFF after 3 consecutive trips without a fault. |
| • | The PCM clears the history DTC after 40 consecutive warm-up cycles without a fault. |
| • | You perform the scan tool Clear DTC Information function. |
Diagnostic Aids
If a DTC P0031 is intermittent, driving the vehicle under the conditions outlined in the Inspection/Maintenance (I/M) section can verify whether the fault is present. Refer to Inspection/Maintenance Heated Oxygen Sensor Heater System Set .
An intermittent malfunction may be caused by a problem in the HO2S 1 electrical circuit. Inspect the wiring harness and the components for an intermittent condition. Refer to Intermittent Conditions .
If a DTC P0031 cannot be duplicated, the information included in the Freeze Frame data can be useful in determining vehicle operating conditions when the DTC was first set.
Test Description
The numbers below refer to the step numbers in the diagnostic table.
-
The Diagnostic System Check-Engine Controls prompts the technician to complete some basic checks and store the freeze frame data on the scan tool if applicable. This creates an electronic copy of the data taken when the fault occurred. The information is then stored in the scan tool for reference.
-
The PCM turns ON the HO2S heater when the engine is running. A test lamp that is ON steady or flashing, indicates that the HO2S heater control circuit is OK.
-
Clearing the DTCs by removing the DOME fuse also clears the PCM long term memory. Using the scan tool to clear DTCs leaves the long term memory active. DTC emitting diagnostics may not run to completion as expected unless the long term memory is cleared. Removal of the DOME fuse also clears the time display of the radio. The DTC P0031 diagnostic can be monitored on the scan tool under the Not Ran Since Code Cleared selection in the DTC Information menu. If a DTC P0031 appears in the Not Ran Since Code Cleared list, the DTC P0031 diagnostic has not yet run. When the DTC P0031 does not appear in the Not Ran Since Code Cleared list, the DTC P0031 diagnostic has run. If the MIL is NOT illuminated, and there is no Pending DTC Status in DTC Information, the DTC P0031 diagnostic has passed. The DTCs MUST be cleared in order to view the Current Status of the Not Ran Since Code Cleared list. DO NOT forget that the Not Ran Since Code Cleared list only indicates that the test has run, not whether the test passed of failed. The DTC Information screen must be checked for Current or Pending status, in order to determine the outcome of the diagnostic test involved.
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
Schematic Reference: Engine Controls Schematics | ||||
Did you perform the Diagnostic System Check-Engine Controls? | -- | Go to Step 2 | ||
2 |
Does the test lamp illuminate? | -- | Go to Step 3 | Go to Step 7 |
3 |
Is the HO2S heater resistance within the specified range? | 4.5-5.7 ohms at 20°C (68°F) | Go to Step 4 | Go to Step 9 |
Did the test lamp illuminate only when the engine was running? | -- | Go to Diagnostic Aids | Go to Step 5 | |
5 |
Is the voltage more than the specified value? | 10 V | Go to Step 8 | Go to Step 6 |
6 | Repair the open circuit or the short to ground in the HO2S heater control circuit. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 11 | -- |
7 | Repair the open in the ignition positive voltage circuit. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 11 | -- |
8 |
Was a repair necessary? | -- | Go to Step 11 | Go to Step 10 |
9 | Replace the HO2S 1. Refer to Heated Oxygen Sensor 1 Replacement . Did you complete the replacement? | -- | Go to Step 11 | -- |
10 | Replace the PCM. Refer to Powertrain Control Module Replacement . Did you complete the replacement? | -- | Go to Step 11 | -- |
Does the DTC run and pass? | -- | Go to Step 12 | Go to Step 2 | |
12 | With a scan tool, observe the stored information, Capture Info. Does the scan tool display any DTCs that you have not diagnosed? | -- | System OK | |
