P0138

CIRCUIT DESCRIPTION
The Heated Oxygen Sensor (HO2S) produces a voltage that varies between 100-900 mV under normal operating conditions. The Engine Control Module (ECM) produces a bias voltage on the HO2S signal circuit of 420-480 mV. The reference ground for the sensor is provided through the ECM. The ECM monitors the signal voltage to determine if the exhaust is lean or rich. The oxygen sensor voltage is high when the exhaust is rich, and low when the exhaust is lean. The ECM constantly monitors the HO2S signal during the Closed Loop operation.

CONDITIONS FOR RUNNING THE DTC
^ The engine is running.
^ The battery voltage is more than 11 volts.
^ The catalytic converter temperature is less than 800°C (1472°F).

CONDITIONS FOR SETTING THE DTC
The HO2S voltage is more than 1080 mV (1.08 volts) for more than 5.1 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.
^ Use a scan tool in order to clear the MIL and the DTC.

DIAGNOSTIC AIDS
Use the J 35616-A Connector Test Adapter Kit for any test that requires probing the ECM harness connector or a component harness connector.

If the condition that set this Diagnostic Trouble Code (DTC) is not present, check for the following conditions:
^ Heated oxygen sensor wiring-Check for the following conditions:
- A signal wire intermittently shorted to voltage
- A reference ground wire with high resistance or intermittently open
- Corrosion and water intrusion at the HO2S connector or the ECM connector
- An oxygen supply inside of the HO2S is necessary for a proper operation. This supply of oxygen is provided through the HO2S wires. All of the HO2S wires and connections should be inspected for any breaks or any contamination. If any wiring repairs need to be made, refer to Wiring Repairs in Diagrams.
^ An intermittent rich engine condition such as the following:
- Evaporative Emission (EVAP) canister purge system malfunction
- Fuel contaminated engine oil
- Incorrect fuel pressure
- Rich fuel injectors
- An inaccurate Mass Air Flow (MAF) sensor
- A rich condition during decel fuel cut-off operation
^ A silicon contaminated HO2S
^ Poor ECM grounds

TEST DESCRIPTION

Steps 1-8:

Steps 9-16:

The numbers below refer to the step numbers on the diagnostic table.
2. The engine must be at the normal operating temperature before performing this test.
3. Using the Freeze Frame data may aid in locating an intermittent condition. If the DTC cannot be duplicated, review the information in the Freeze Frame. Try to operate the vehicle within the same Freeze Frame conditions, the RPM, the MAF, the vehicle speed, the temperature etc., that were noted. This process may help in recreating the condition that set the DTC.
6. The ECM provides the reference ground for the oxygen sensor. A small amount of current will appear on this circuit when the ECM is operational. The measured resistance of the circuit will increase when the ECM is operational. This is considered normal.
9. Monitor the HO2S voltage of the opposite bank sensor. If the voltage activity of the opposite bank sensor is similar to the voltage activity of the suspect sensor, check for rich conditions that would affect both cylinders. An opposite bank sensor with normal HO2S activity indicates a rich condition exists only on the suspect HO2S cylinder bank or a fault in the circuit.
12. An HO2S contaminated by silicon will have a white, powdery deposit on the portion of the HO2S that is exposed to the exhaust stream. The usual cause of silica contamination is the use of unapproved silicon RTV sealer or the use of silicon based sprays or fluids within the engine. If the cause of this contamination is not corrected, the replacement HO2S will also get contaminated.