Circuit Description
The heated oxygen sensor (HO2S) must reach operating temperature to provide an accurate voltage signal. A heating element inside the HO2S minimizes the time required for the sensor to reach operating temperature. Voltage is provided to the heater by the ignition 1 voltage circuit through a fuse. With the engine running, ground is provided to the heater by the HO2S heater low control circuit, through a low side driver within the engine control module (ECM). The ECM commands the heater ON or OFF to maintain a specific HO2S operating temperature range. The ECM monitors the voltage on the HO2S heater low control circuit for the heater fault diagnosis. If the ECM detects that the voltage is less than a specified value with the driver OFF, DTCs P0031 or P0037 sets.
Conditions for Running the DTC
| • | The Ignition 1 parameter is more than 10.9 volts. |
| • | The ignition is ON, with the engine OFF. |
| • | The HO2S heater command parameter is OFF. |
Conditions for Setting the DTC
The ECM detects that the affected HO2S Heater low control circuit voltage is less than 1.25 volts.
Action Taken When the DTC Sets
| • | The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails. |
| • | The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records. |
Conditions for Clearing the MIL/DTC
| • | The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail. |
| • | A current DTC, Last Test Failed, clears when the diagnostic runs and passes. |
| • | A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic. |
| • | Clear the MIL and the DTC with a scan tool. |
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
Schematic Reference: Engine Controls Schematics Connector End View Reference: Engine Controls Connector End Views or Engine Control Module Connector End Views | ||||
1 | Did you perform the Diagnostic System Check-Engine Controls? | -- | Go to Step 2 | |
2 |
Is the HO2S heater current parameter within the specified range? | 0.249-1.502 A | Go to Step 3 | Go to Step 4 |
3 |
Did the DTC fail this ignition? | -- | Go to Step 4 | Go to Intermittent Conditions |
4 | Inspect the ERLS fuse. Is the ERLS fuse open? | -- | Go to Step 5 | Go to Step 6 |
5 | Test the ignition 1 voltage circuit for a short to ground or for a short to the low signal circuit. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 17 | Go to Step 8 |
6 |
Does the test lamp illuminate? | -- | Go to Step 7 | Go to Step 14 |
7 |
Does the test lamp turn ON and OFF with each command? | -- | Go to Step 12 | Go to Step 9 |
8 |
Important: Perform the following test on all HO2S' which are supplied voltage by the suspect circuit. Test the ignition 1 voltage circuit on the sensor side of the HO2S connector for a short to ground or for a short to the low signal circuit. Refer to Circuit Testing in Wiring Systems. Is any sensor shorted to ground? | -- | Go to Step 15 | Go to Intermittent Conditions |
9 | Does the test lamp remain illuminated with each command? | -- | Go to Step 10 | Go to Step 11 |
10 | Test the HO2S heater low control circuit for a short to ground or for a short to the low signal circuit. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 17 | Go to Step 16 |
11 | Test the HO2S heater low control circuit for an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 17 | Go to Step 13 |
12 | Test for an intermittent and for a poor connection at the HO2S. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 17 | Go to Step 15 |
13 | Test for an intermittent and for a poor connection at the ECM. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 17 | Go to Step 16 |
14 | Repair the open in the ignition 1 voltage circuit. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 17 | -- |
15 | Replace the affected HO2S. Refer to Heated Oxygen Sensor 1 Replacement or Heated Oxygen Sensor 2 Replacement . Did you complete the replacement? | -- | Go to Step 17 | -- |
16 | Replace the ECM. Refer to Engine Control Module Replacement . Did you complete the replacement? | -- | Go to Step 17 | -- |
17 |
Did the DTC fail this ignition? | -- | Go to Step 2 | Go to Step 18 |
18 | Observe the Capture Info with a scan tool. Are there any DTCs that have not been diagnosed? | -- | System OK | |
