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 DTC:
DTC P0138 HO2S Circuit High Voltage Sensor 2
Conditions for Running the DTC
| • | The engine is running. |
| • | The DTC runs continuously when the above condition is met. |
Conditions for Setting the DTC
The ECM detects that the HO2S voltage is more than 1200 mV.
Action Taken When the DTC Sets
| • | The malfunction indicator lamp (MIL) will illuminate after 3 consecutive trips with a fail. |
| • | The ECM will record operating conditions at the time the diagnostic fails. This information will be stored in the Freeze Frame and Failure Records buffers. |
| • | A history DTC is stored. |
Conditions for Clearing the MIL/DTC
| • | The MIL will turn OFF after 4 consecutive ignition cycles in which the diagnostic runs without a fault. |
| • | DTCs can be cleared by using the scan tool. |
| • | Disconnect the ECM battery feed for 10 seconds. |
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 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 2 signal circuit for a short to voltage. Refer to Circuit Testing and Wiring Repairs . 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 . 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 . Did you find and correct the condition? | -- | Go to Step 11 | Go to Step 10 | ||||||||||||
9 | Replace the HO2S. Refer to Heated Oxygen Sensor 2 Replacement . 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 | Are there any DTCs that have not been diagnosed? | -- | System OK | |||||||||||||
