For 1990-2009 cars
Engine Controls Components
Heated Oxygen Sensors
OBD II Symbol Description Notice
Handling ESD Sensitive Parts Notice

### Circuit Description

The wide band heated oxygen sensor (HO2S) measures the amount of oxygen in the exhaust stream more quickly and accurately than the switching style HO2S. The wide range HO2S sensor functions more like an air fuel sensor. The wide band sensor consists of an oxygen sensing cell, an oxygen pumping cell, and a heater. The exhaust gas sample passes through a diffusion gap between the sensing cell and the pumping cell. The engine control module (ECM) supplies a signal voltage to the HO2S and uses this voltage as a reference to the amount of oxygen in the exhaust system. An electronic circuit within the ECM controls the pump current through the oxygen pumping cell in order to maintain a constant signal voltage. The ECM monitors the voltage variation on the signal circuit and attempts to keep the voltage constant by increasing or decreasing the amount of current flow or reversing the direction of the current flow to the pumping cell. By measuring the direction and amount of current required to maintain the signal voltage, the ECM can determine the concentration of oxygen in the exhaust. The signal voltage is displayed as a lambda value. A lambda value of 1 is equal to a stoichiometric air fuel ratio of 14.7:1. Under normal operating conditions, the lambda value will remain around 1. When the system is lean, the oxygen level will be high and the lambda signal will be high or more than 1. When the oxygen level is low, the lambda signal will be low or less than 1. The ECM uses this information to maintain the proper air/fuel ratio.

### Conditions for Running the DTC

• | Engine at operating temperature

• | The engine speed must be between 1400 and 2400 RPM.

• | Engine load 8-12 percent

• | Mass air flow 18-22 g/s

• | Throttle position 6-10 percent

• | The same bank sensor 2 HO2S diagnosis is completed.

• | No same bank sensor 2 HO2S DTCs present.

### Conditions for Setting the DTC

• | The ECM has determined that the difference between the front and the rear sensor signals is more than expected.

• | The above condition is met for more than 2 seconds.

### Action Taken When the DTC Sets

The ECM illuminates the malfunction indicator lamp (MIL) and records the operating conditions in the Freeze Frame on the second consecutive drive trip that the diagnostic runs and fails.

### Conditions for Clearing the MIL/DTC

• | The ECM turns OFF the MIL after three consecutive drive trips that the diagnostic runs and passes.

• | A History DTC clears after forty consecutive warm-up cycles in which no failures are reported by this diagnostic or any other emission related diagnostic.

• | The scan tool clears the MIL/DTC.

### 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.

Check for the following conditions:

• | Inspect for loose or poor ECM grounds.

• | A possible cause for this DTC is an exhaust leak between sensor 1 and sensor 2. Inspect the exhaust system for any leaks.

### Test Description

The numbers below refer to steps on the diagnostic table.

1. Any exhaust leak, even a small one, can affect the operation of the HO2S. The ECM compares the reading of sensor 1 with the reading from sensor 2 as part of the diagnosis. A leak between sensor 1 and sensor 2 may set a DTC.

2. A short between the signal circuit and the reference ground circuit or the pump current input and output circuits may not appear on the voltage tests. The ECM must be disconnected and each circuit tested for continuity with the other HO2S circuits.

#### Heated Oxygen Sensor (HO2S) Circuit Sensor 1

Step | Action | Values | Yes | No
--- | --- | --- | --- | ---
1 | Did you perform the Powertrain On-Board Diagnostic (OBD) System check? | -- | Go to Step 2 | Go to Powertrain On Board Diagnostic (OBD) System Check
2 |

1. Using the scan tool, store the DTC information from the ECM into the scan tool.
2. Clear the DTC information from the ECM.
3. Turn OFF the ignition for 15 seconds.
4. Start and idle the engine until normal operating temperature is reached.
5. Operate the vehicle within the conditions for this diagnostic to run or the conditions noted in the Freeze Frame records.
6. Using the scan tool, check for any DTCs.

Did this DTC run and fail this ignition?

--

Go to Step 3

Go to Diagnostic Aids

3 |

1. Inspect the exhaust system for any leaks upstream from the affected oxygen sensor including the AIR distribution system.
2. Inspect for any exhaust leaks between sensor 1 and sensor 2.
3. Repair the exhaust leak as necessary.

Did you find and repair an exhaust leak?

--

Go to Step 16

Go to Step 4

4 |

1. Turn OFF the ignition.
2. Visually/physically inspect the following items:

• | Ensure that the HO2S is securely installed.

• | Check for terminal corrosion or water intrusion.

• | Check the terminal tension at the HO2S connectors.

• | Check for damaged wiring.

3. Repair as necessary. Refer to Wiring Repairs or Connector Repairs in Wiring Systems.

Did you find and correct a problem?

--

Go to Step 16

Go to Step 5

5 |

1. Turn OFF the ignition.
2. Disconnect the connector for the HO2S that applies to this DTC.
3. Turn ON the ignition leaving the engine OFF.
4. Measure the voltage of the HO2S signal circuit at the ECM side of the connector to battery ground.

Is the voltage within the specified value?

2-4 V

Go to Step 6

Go to Step 10

6 | Measure the voltage of the reference ground circuit at the ECM side of the connector to battery ground. Is the voltage within the specified value? | 2-4 V | Go to Step 7 | Go to Step 10
7 | Measure the voltage of the pump current input circuit at the ECM side of the connector to battery ground. Is the voltage within the specified value? | 0.2-0.4 V | Go to Step 8 | Go to Step 10
8 | Measure the voltage of the pump current output circuit at the ECM side of the connector to battery ground. Is the voltage within the specified value? | 0.2-0.4 V | Go to Step 9 | Go to Step 10
9 |

1. Turn OFF the ignition.
2. Disconnect the ECM.
3. Test each of the circuits on the affected HO2S for a short to each other.
4. Repair as necessary. Refer to Wiring Repairs in Wiring Systems.

Did you find and correct a problem?

--

Go to Step 16

Go to Step 13

10 | Was the voltage above the specified value? | -- | Go to Step 12 | Go to Step 11
11 |

1. Test the affected circuit for the following conditions:

• | Open

• | Short to ground

• | High resistance

2. Repair as necessary. Refer to Wiring Repairs in Wiring Systems.

Did you find and repair a problem?

--

Go to Step 16

Go to Step 14

12 |

1. Test the affected circuit for a short to voltage.
2. Repair as necessary. Refer to Wiring Repairs in Wiring Systems.

Did you find and repair a problem?

--

Go to Step 16

Go to Step 14

13 | Replace the HO2S. Refer to Heated Oxygen Sensor Replacement . Is the replacement complete? | -- | Go to Step 16 | --
14 |

1. Check for a poor connection or poor terminal tension at the ECM. 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 repair a problem?

--

Go to Step 16

Go to Step 15

15 | Important:

• | Perform the Idle Learn Procedure when replacing the ECM.

• | This vehicle is equipped with a Theft Deterrent System that interfaces with the 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/Programming .

Is the action complete?

--

Go to Step 16

--

16 |

1. Using the scan tool, clear the DTCs.
2. Start the engine.
3. Allow the engine to idle until the engine reaches the normal operating temperature.
4. Select DTC and the Specific DTC function.
5. Enter the DTC number that was set.
6. Operate the vehicle within the Conditions for Running this DTC until the scan tool indicates that he diagnostic Ran.

Does the scan tool indicate that the diagnostic Passed?

--

Go to Step 17

Go to Step 2

17 | Does the scan tool display any additional undiagnosed DTCs? | -- | Go to the applicable DTC table | System OK