Circuit Description
Heating elements inside the heated oxygen sensor (HO2S) minimize the time required for the sensors to reach operating temperature, and to provide an accurate voltage signal. A low-side driver within the engine control module (ECM) is pulse-width controlled to provide current to the heater elements. During warm-up the ECM will reduce the ON time to prevent thermal shock to the sensor components from moisture in the exhaust system. The ECM will not allow full HO2S heating until calibrated limits of time, temperature, and intake airflow have been reached. The ECM periodically monitors the HO2S operating state by briefly turning OFF the heater low-side driver at regular intervals. A small reference voltage of approximately 3.6 volts is present at the heater low control circuit. When the low-side driver is commanded ON, the reference voltage is low. When the low-side driver is commanded OFF, the reference voltage is high, close to battery voltage. If the ECM detects that the HO2S heater low control circuit voltage is less than 2.6 volts when the heater is commanded OFF, a short to ground is indicated and the following DTCs will set:
| • | DTC P0031 for HO2S bank 1 sensor 1 |
| • | DTC P0037 for HO2S bank 1 sensor 2 |
| • | DTC P0051 for HO2S bank 2 sensor 1 |
| • | DTC P0057 for HO2S bank 2 sensor 2 |
Conditions for Running the DTC
| • | The engine is running. |
| • | The Ignition 1 voltage parameter is 8-18 volts. |
Conditions for Setting the DTC
The ECM detects that the HO2S heater low control circuit voltage is below 2.6 volts when the heater is commanded OFF, indicating a shorted HO2S heater circuit.
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 | Yes | No |
|---|---|---|---|
Schematic Reference: Engine Controls Schematics Connector End View Reference: Engine Control Module Connector End Views or Engine Controls Connector End Views | |||
1 | Did you perform the Diagnostic System Check-Engine Controls? | Go to Step 2 | |
2 |
Did the DTC fail this ignition? | Go to Step 4 | Go to Step 3 |
3 |
Did the DTC fail this ignition? | Go to Step 4 | Go to Intermittent Conditions |
4 |
Important: The test lamp may flash OFF-ON as the engine control module (ECM) commands the sensor heating operation. Does the test lamp illuminate? | Go to Step 5 | Go to Step 6 |
5 |
Does the test lamp illuminate? | Go to Step 7 | Go to Step 8 |
6 | Test the affected HO2S heater low control circuit for an open or for high resistance. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 12 | Go to Step 9 |
7 | Test the affected HO2S heater low control circuit for a short to ground or for a short the HO2S low signal circuit. Refer to Circuit Testing and Wiring Repairs Wiring Systems. Did you find and correct the condition? | Go to Step 12 | Go to Step 9 |
8 | Test for an intermittent and for a poor connection at the harness connector of the affected 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 12 | Go to Step 10 |
9 | Test for an intermittent and for a poor connection at the harness connector of 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 12 | Go to Step 11 |
10 | Replace the affected HO2S. Refer to Heated Oxygen Sensor Replacement - Bank 1 Sensor 1 , Heated Oxygen Sensor Replacement - Bank 1 Sensor 2 , Heated Oxygen Sensor Replacement - Bank 2 Sensor 1 , or Heated Oxygen Sensor Replacement - Bank 2 Sensor 2 . Did you complete the replacement? | Go to Step 12 | -- |
11 | Replace the ECM. Refer to Engine Control Module Replacement . Did you complete the replacement? | Go to Step 12 | -- |
12 |
Did the DTC fail this ignition? | Go to Step 2 | Go to Step 13 |
13 | Observe the Capture Info with a scan tool. Are there any DTCs that have not been diagnosed? | System OK | |
