Circuit Description
The DTC P0031 Heated Oxygen Sensor (HO2S) Heater Control Circuit Low Voltage Sensor 1 diagnostic monitors the operation of the HO2S 1 heater circuit. The heaters in the oxygen sensors increase the amount of time the sensor spends in Closed Loop fuel control operation or catalyst monitoring operation. The oxygen sensor heater greatly reduces the amount of time required for the fuel control HO2S 1 to become active. The heater helps provide accurate oxygen content readings of the engine exhaust by the HO2S.
DTC Descriptor
This diagnostic procedure supports the following DTC:
DTC P0031 Heated Oxygen Sensor (HO2S) Heater Control Circuit Low Voltage Sensor 1
Conditions for Running the DTC
| • | The battery is between 10.5-16 volts. |
| • | The engine has been operating for at least 10 seconds. |
| • | The heater control circuit duty cycle is more than 50 percent. |
| • | No current misfire is detected. |
| • | DTC P0031 runs continuously once the above conditions have been met. |
Conditions for Setting the DTC
| • | The HO2S 1 heater is commanded ON for more than 0.2 seconds. |
| • | The HO2S 1 heater current is less than 0.8 amps. |
| • | The condition exists for more than 10 seconds. |
Action Taken When the DTC Sets
| • | The powertrain control module (PCM) illuminates the malfunction indicator lamp (MIL). |
| • | The PCM records the operating conditions at the time the diagnostic fails. This information is stored in the Freeze Frame buffer. |
| • | The PCM will turn OFF the heater in the oxygen sensor. |
Conditions for Clearing the MIL/DTC
| • | The MIL turns OFF after 3 consecutively passing trips without a fault present. |
| • | A History DTC clears after 40 consecutive warm-up cycles without a fault. |
| • | Use the scan tool Clear DTC Information function in order to clear the DTC. |
Test Description
The numbers below refer to the step numbers on the diagnostic table.
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The Diagnostic System Check - Vehicle 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 later reference.
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This step checks whether the malfunction that caused the DTC P0031 is still present. Operating the vehicle in check mode enhances the diagnostic capabilities of the PCM. The HO2S Heater diagnostic can be monitored on the scan tool under the I/M System Information selection of System Information. When the HO2S Heater test displays a YES status, indicating that the oxygen sensor heater diagnostic is completed, check for a DTC P0031 in the Last Test Failed screen of the scan tool. If there is no DTC P0031 displayed the HO2S heater diagnostic has run and passed, indicating that no malfunction was present this time. The DTCs MUST be cleared in order to view the Current Status of the system diagnostics being performed. Do not forget that I/M System Information tests only indicate that the test has run, not whether the test passed or failed. The Last Test Failed screen must be checked for related DTCs in order to determine the outcome of the diagnostic test involved. For additional information on check mode operation refer to Powertrain Control Module Diagnosis.
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This step tests the HO2S ground circuit at the PCM. In order for the PCM to operate the HO2S 1 heater control circuit, the ground circuit to C2-7 must be good.
Step | Action | Value | Yes | No |
|---|---|---|---|---|
Schematic Reference: Engine Controls Schematics Connector End View Reference: Powertrain Control Module Connector End Views or Engine Controls Connector End Views | ||||
Did you perform the Diagnostic System Check - Vehicle? | -- | Go to Step 2 | ||
Did a DTC P0031 set? | -- | Go to Step 3 | Go to Intermittent Conditions | |
3 |
Is the resistance of the sensor within the specified range? | 1.8-3.4 ohms at 20°C (68°F) | Go to Step 4 | Go to Step 12 |
4 |
Does the test lamp illuminate? | -- | Go to Step 5 | Go to Step 11 |
5 |
Does the test lamp illuminate? | -- | Go to Step 6 | Go to Step 7 |
6 |
Did the test lamp turn OFF or flash ON and Off with the engine running? | -- | Go to Intermittent Conditions | Go to Step 9 |
7 | Test the heater control circuit of the HO2S 1 for an open or a high resistance. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | -- | Go to Step 14 | Go to Step 8 |
8 | Test for an intermittent and for a poor connection at the HO2S 1. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs . Did you find and correct the condition? | -- | Go to Step 14 | Go to Step 12 |
Test for an open or high resistance in the HO2S ground circuit between C2-7 and G104. Refer to Circuit Testing and Connector Repairs . Did you find and correct the condition? | -- | Go to Step 14 | Go to Step 10 | |
10 | Test for an intermittent and for a poor connection at the PCM. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs . Did you find and correct the condition? | -- | Go to Step 14 | Go to Step 13 |
11 |
Did you complete the repair? | -- | Go to Step 14 | -- |
12 | Replace the HO2S 1. Refer to Heated Oxygen Sensor 1 Replacement . Did you complete the replacement? | -- | Go to Step 14 | -- |
13 | Replace the PCM. Refer to Control Module References for replacement, setup, and programming. Did you complete the replacement? | -- | Go to Step 14 | -- |
14 |
Does the DTC run and pass? | -- | Go to Step 15 | Go to Step 2 |
15 | Observe the Capture Info with a scan tool. Are there any DTCs that you have not diagnosed? | -- | System OK | |
