For 1990-2009 cars

### 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.

• | Clear the MIL and the DTC with a scan tool.

### Diagnostic Aids

Use the J 35616 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 Wiring Systems.

• | 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

The numbers below refer to the step numbers on the diagnostic table.

1. The engine must be at the normal operating temperature before performing this test.

2. 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.

3. 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.

4. 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.

5. 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.

#### P0138 or P0158 Heated Oxygen Sensor (HO2S) Circuit High Voltage Sensor 2

Step | Action | Values | Yes | No
--- | --- | --- | --- | ---
Schematic Reference: Engine Controls Schematics
1 | Did you perform the Diagnostic System Check-Engine Controls? | -- | Go to Step 2 | Go to Diagnostic System Check - Engine Controls
2 |

1. Install the scan tool.
2. Allow the engine to run at the normal operating temperature.
3. Operate the vehicle within the Conditions For Running the DTC.
4. Using a scan tool, monitor the HO2S voltage for this sensor.

Is the HO2S voltage more than the specified value?

1,080 mV

Go to Step 4

Go to Step 3

3 |

1. Turn ON the ignition, with the engine OFF.
2. Review the Freeze Frame data for this DTC and note the parameters.
3. Clear the DTCs.
4. Turn OFF the ignition for 15 seconds.
5. Start the engine.
6. Operate the vehicle within the Conditions For Running the DTC, or as close to the data observed in the Freeze Frame/Failure Records.
7. Check for any DTCs.

Did the DTC fail this ignition?

--

Go to Step 4

Go to Diagnostic Aids

4 |

1. Turn OFF the ignition.
2. Disconnect the HO2S.
3. Turn ON the ignition, with the engine OFF.
4. Using a scan tool, monitor the HO2S voltage for the sensor that applies to this DTC.

Is the HO2S voltage within the specified range?

420-480 mV

Go to Step 6

Go to Step 5

5 |

1. Turn OFF the ignition.
2. Disconnect the engine control module (ECM) connector C1.
3. Turn ON the ignition.
4. Using a DMM, measure the voltage from the HO2S signal circuit in the ECM harness connector to the battery ground.

Is there any voltage present?

--

Go to Step 10

Go to Step 13

6 |

Important: Make sure the ECM has shut down prior to measuring the reference ground circuit resistance. This can be verified by the loss of communication on the scan tool.

1. Turn OFF the ignition for 30 seconds.

Important: Do not use a test lamp to test the continuity of the reference ground circuit. Damage to the ECM will result.

2. Using the DMM, measure the resistance of the HO2S reference ground circuit to battery ground.

Is the resistance less than the specified value?

5 ohms

Go to Step 9

Go to Step 7

7 |

1. Disconnect the ECM connector C1.
2. Test the HO2S reference ground circuit for an open or high resistance.
3. Repair as necessary. Refer to Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 15

Go to Step 8

8 | Measure the resistance from the ground stud at the ECM bracket to battery ground. Is the resistance less than the specified value? | 5 ohms | Go to Step 13 | Go to Step 11
9 |

1. Inspect for any of the following conditions:

• | HO2S connector for water intrusion

• | Silicon contaminated HO2S

• | Fuel contaminated engine oil

• | Evaporative emission (EVAP) canister purge system malfunction

• | Incorrect fuel pressure

• | Leaking fuel pressure regulator

• | Rich fuel injectors

• | An inaccurate MAF sensor

2. Repair any of the above or similar conditions as necessary.

Did you find and correct the condition?

--

Go to Step 15

Go to Step 12

10 | Repair the signal circuit that is shorted to voltage. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 15 | --
11 | Repair the high resistance in the ECM ground circuit. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 15 | --
12 | Important: Before replacing a contaminated HO2S, determine and repair the cause of the contamination. Replace the HO2S. Refer to Heated Oxygen Sensor Replacement . Did you complete the replacement? | -- | Go to Step 15 | --
13 |

1. Check for a poor connection or poor terminal tension at the ECM harness connector. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.
2. Repair as necessary. Refer to Connector Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 15

Go to Step 14

14 | Important:

• | Perform the idle learn procedure when replacing the ECM or the throttle body.

• | This vehicle is equipped with a theft deterrent system which interfaces with the engine control module (ECM). Program the new ECM with the frequency code of the theft deterrent module that is currently on the vehicle.

Replace the ECM. Refer to Engine Control Module Replacement .

Did you complete the action?

--

Go to Step 15

--

15 |

1. Use the scan tool in order to clear the DTCs.
2. Turn OFF the ignition for 30 seconds.
3. Start the engine.
4. Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text.

Does the DTC run and pass?

Go to Step 16

Go to Step 2

16 | With a scan tool, observe the stored information, Capture Info. Does the scan tool display any DTCs that you have not diagnosed? | -- | Go to Diagnostic Trouble Code (DTC) List | System OK