Circuit Description
The engine control module (ECM) supplies a voltage near 450 mV between the heated oxygen sensor (HO2S) high signal circuit and the low reference circuit. The HO2S varies the voltage over a range from about 1,000 mV when the exhaust is rich, down through about 10 mV when the exhaust is lean.
The ECM monitors and stores the HO2S voltage information. The ECM evaluates the HO2S voltage samples in order to determine the amount of time that the HO2S voltage was out of range. The ECM compares the stored HO2S voltage samples taken within each sample period and determines if the majority of the samples are out of the operating range.
The HO2S utilizes the following circuits:
| • | A signal circuit |
| • | A low reference circuit |
| • | An ignition 1 voltage circuit |
| • | A heater control circuit |
The ECM monitors the HO2S voltage for being fixed above a predetermined voltage. If the ECM detects the voltage is too high, the DTC sets.
DTC Descriptor
This diagnostic procedure supports the following DTCs:
| • | DTC P0138 HO2S Circuit High Voltage Bank 1 Sensor 2 |
| • | DTC P0158 HO2S Circuit High Voltage Bank 2 Sensor 2 |
Conditions for Running the DTC
| • | The engine is running. |
| • | The ignition 1 voltage is more 10 volts. |
| • | The DTCs run continuously once the above condition are met for 10 milliseconds. |
Conditions for Setting the DTC
The ECM detects that the HO2S voltage is more than 1200 mV for 5 seconds.
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 | Values | 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 |
Is the voltage more than the specified value? | 900 mV | Go to Step 4 | Go to Step 3 | ||||||||||||
3 |
Did the DTC P0138 or P0158 fail this ignition? | -- | Go to Step 4 | Go to Intermittent Conditions | ||||||||||||
4 |
Is the voltage more than the specified value? | 900 mV | Go to Step 5 | Go to Step 6 | ||||||||||||
5 | Test the HO2S signal circuit for a short to voltage. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 11 | Go to Step 8 | ||||||||||||
6 | Test or inspect for the following conditions:
Did you find and correct the condition? | -- | Go to Step 11 | Go to Step 7 | ||||||||||||
7 | Test for shorted terminals and for poor connections at the harness connector of 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 11 | Go to Step 9 | ||||||||||||
8 | Test for shorted terminals and for poor connections at the harness connector of the engine control module (ECM). Refer to Testing for Intermittent Conditions and Poor Connections and Repairing Connector Terminals in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 11 | Go to Step 10 | ||||||||||||
9 | Replace the appropriate HO2S. Did you complete the replacement? | -- | Go to Step 11 | -- | ||||||||||||
10 | Replace the ECM. Refer to Engine Control Module Replacement . Did you complete the replacement? | -- | Go to Step 11 | -- | ||||||||||||
11 |
Did the DTC fail this ignition? | -- | Go to Step 2 | Go to Step 12 | ||||||||||||
12 | Observe the Capture Info with a scan tool. Are there any DTCs that have not been diagnosed? | -- | System OK | |||||||||||||
