For 1990-2009 cars
Engine Controls Components
Cell 20: Heated Oxygen Sensors
OBD II Symbol Description Notice
Handling ESD Sensitive Parts Notice

### Circuit Description

The heated oxygen sensor (HO2S) produces a voltage that varies between 100 mV and 900 mV under normal operating conditions. The engine control module (ECM) produces a bias voltage on the HO2S signal circuit of 420 to 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 rear HO2S is in closed loop.

• | The battery voltage is more than 11 volts.

### Conditions for Setting the DTC

• | The rear HO2S is stuck above 600 mV.

• | The rear HO2S is stuck below 600 mV.

• | The oxygen sensor voltage is more than 200 mv during decel fuel cut off operation.

### Action Taken When the DTC Sets

• | The ECM will illuminate the malfunction indicator lamp (MIL) on the second consecutive drive trip that the diagnostic runs and fails.

• | The ECM will record operating conditions in Freeze Frame on the first drive trip that the diagnostic runs and fails (Fail Pending).

### 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 if no failures report by this diagnostic or any other emission related diagnostic.

• | The ECM battery voltage is interrupted.

• | The scan tool clears the MIL/DTC.

### Diagnostic Aids

Notice: Using the J 35616-A Connector Test Adapter Kit will prevent damage to the harness connector terminals.

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 conditions to set this DTC are not present, check for the following conditions:

• | Heated oxygen sensor wiring--Check for the following conditions:

- | A signal wire intermittently open, shorted to ground, or with excessive circuit resistance

- | A reference ground wire intermittently open, shorted to ground, or with excessive circuit resistance

- | The sensor pigtail or the harness may be mis-positioned and contacting the exhaust system.

- | 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 breaks or contamination. If any wiring requires repair, refer to Wiring Repairs in Wiring Systems.

- | Inspect the connectors for the following conditions:

• | Proper mating

• | Broken locks

• | Improperly formed or damaged terminals

• | Corrosion and water intrusion

• | A contaminated HO2S--Contamination can include the following:

- | Fuel contamination

- | Use of incorrect RTV sealant

- | Excessive oil or coolant consumption

• | Exhaust leaks--An exhaust leak may cause the outside air to be pulled into the exhaust gas stream past the HO2S, causing this DTC to set. Check for any exhaust leaks near the HO2S.

• | Improperly torqued HO2S

• | Inoperative HO2S heater

• | Poor ECM grounds

### Test Description

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

1. Conditions located in the Freeze Frame may indicate if the test failed during normal operating conditions or during a decel fuel cut off condition. If the test failed during a decel fuel cut off condition, operate the vehicle under a decel condition and monitor the HO2S voltage while watching for high sensor voltage during this operating condition. High HO2S voltage during a decel fuel cut off operation indicates that a rich condition exists while the injectors are turned off. Leaking fuel injectors or a leaking fuel pressure regulator may be the cause.

2. Depending on the operating conditions, the heater operation may be modulated or operated continuously. This will be indicated by the test lamp flashing or staying illuminated. This is considered normal operation.

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. The ECM provides the reference ground for the oxygen sensor. A short to ground on this circuit will cause the signal voltage to shift.

5. An oxygen supply inside the HO2S is necessary for proper operation. This supply of oxygen is provided through the HO2S wires. Inspect all HO2S wires and connections for breaks or contamination.

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 | Are any other powertrain component DTCs set? | -- | Go to the applicable DTC | Go to Step 3
3 |

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 required 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 4

Go to Diagnostic Aids

4 |

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

Did you find and repair an exhaust leak?

--

Go to Step 21

Go to Step 5

5 |

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

Does the scan tool indicate that the HO2S voltage is within the specified range?

420-480 mv

Go to Step 6

Go to Step 12

6 |

1. Turn OFF the ignition.

Important: Do not use the HO2S reference ground for this test. The use of the reference ground circuit may produce inaccurate results.

2. Jumper the HO2S signal circuit to a known good ground.
3. Turn ON the ignition leaving the engine OFF.
4. Using the scan tool, monitor the HO2S voltage for the sensor that applies to this DTC.

Is the voltage at the specified value?

0 mv

Go to Step 7

Go to Step 13

7 |

1. Remove the jumper from the HO2S signal circuit.
2. Connect a test lamp between the switched B+ circuit and the heater control circuit.
3. Start the engine and allow it to idle.
4. Observe the test lamp.

Does the test lamp illuminate or flash?

--

Go to Step 8

Go to Step 16

8 |

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 J 39200 DMM, measure the resistance of the HO2S reference ground circuit to battery ground.

Is the resistance of the circuit less than specified value?

5 ohms

Go to Step 10

Go to Step 9

9 |

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

Did you find and repair a problem?

--

Go to Step 21

Go to Step 11

10 |

1. Disconnect the ECM connector (C1).
2. Using the J 39200 DMM, measure the resistance of the HO2S reference ground circuit to battery ground.

Is the resistance at the specified value?

∞

Go to Step 17

Go to Step 15

11 | 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 19 | Go to Step 14
12 |

1. Leave the HO2S disconnected.
2. Turn OFF the ignition.
3. Disconnect the ECM.
4. Turn ON the ignition.
5. Test the HO2S signal circuit for a short to ground or a short to voltage.
6. Repair as necessary. Refer to Wiring Repairs in Wiring Systems.

Did you find and repair a problem?

--

Go to Step 21

Go to Step 19

13 |

1. Turn OFF the ignition.
2. Remove the jumper from the signal circuit.
3. Disconnect the ECM connector (C1).
4. Test the HO2S signal circuit for an open or high resistance.
5. Repair as necessary. Refer to Wiring Repairs in Wiring Systems.

Did you find and repair a problem?

--

Go to Step 21

Go to Step 19

14 | Repair the high resistance in the ECM ground circuit. Refer to Wiring Repairs in Wiring Systems. Is the repair complete? | -- | Go to Step 21 | --
15 | Repair the short to ground in the HO2S reference ground circuit. Refer to Wiring Repairs in Wiring Systems. Is the repair complete? | -- | Go to Step 21 | --
16 | Diagnose and repair the inoperative heater control circuit. Refer to DTC P1141 HO2S Heater Control Circuit Bank 1 Sensor 2 or DTC P1161 HO2S Heater Control Circuit Bank 2 Sensor 2 . Is the repair complete? | -- | Go to Step 21 | --
17 | 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 and at the ECM. Refer to Checking Terminal Contact in Engine Control Module Diagnosis .

• | Check for damaged wiring.

• | Repair as necessary. Refer to Wiring Repairs in Wiring Systems.

Did you find and correct a problem?

--

Go to Step 21

Go to Step 18

18 | Replace the HO2S. Refer to Heated Oxygen Sensor Replacement . Is the action complete? | -- | Go to Step 21 | --
19 | Check for a poor connection or poor terminal tension at the ECM harness connector. Refer to Wiring Repairs in Wiring Systems. Also, refer to Checking Terminal Contact in Engine Control Module Diagnosis . Did you find and correct a problem? | -- | Go to Step 21 | Go to Step 20
20 | Important:

• | Perform the Idle Learn Procedure when replacing the ECM and the throttle body.

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

Is the action complete?

--

Go to Step 21

--

21 |

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 the diagnostic Ran.

Does the scan tool indicate the diagnostic Passed?

--

Go to Step 22

Go to Step 2

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