For 1990-2009 cars

### Circuit Description

The heated oxygen sensor (HO2S) heater circuit reduces the time required for the oxygen sensor to reach operating temperature and maintains the operating temperature during extended idle periods. When the ignition is turned to the ON position, voltage is supplied to the sensor heater from the engine controls power relay through a fuse. The engine control module (ECM) controls the heater operation by first modulating the ground circuit when the sensors are cold, and then turning the heaters on continuously after a predetermined amount of time. This prevents the possibility of thermal shock to the sensor by controlling the sensors rate of heating. Once the sensor reaches operating temperature, the ECM may again modulate the ground.

### Conditions for Running the DTC

• | The battery voltage is more than 9 volts.

• | The engine is running.

• | The sensor heater is ON.

### Conditions for Setting the DTC

A fault is detected in the heater control circuit.

### 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.

An open fuse in the HO2S heater circuit may be caused by the heater element in one of the sensors. The condition may not be present until the sensor operates for a period of time. If no fault is present in the heater circuit, monitor the amperage of each heater using the DMM to determine if one of the heater elements is the cause of the open fuse.

Check for the following conditions:

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

• | An intermittent or poor connection or corrosion, in the connector--Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.

### Test Description

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

1. Multiple HO2S DTCs will set if the supply voltage to the sensor heaters is open.

1. The test lamp may illuminate or flash depending on the operating conditions. This indicates the ECM and the control circuit are functioning. The engine must be running for the ECM to operate the control circuit.

2. 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.

#### DTC P1141 or P1161 Heated Oxygen Sensor (HO2S) Heater Control Circuit 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 | Using the scan tool, observe the DTC information. Are DTCs P0135, P0141, P0155, P0161, P1141 or P1161 set? | -- | Go to Step 3 | Go to Step 4
3 |

1. Turn OFF the ignition.
2. Inspect fuse 43 for the oxygen sensor heaters located in the ECM housing.

Is fuse 43 open?

--

Go to Step 16

Go to Step 17

4 | Inspect the exhaust system for leaks upstream from the affected oxygen sensor including the AIR distribution system. Did you find the condition? | -- | Go to Step 18 | Go to Step 5
5 | Important: The ignition must be OFF when connecting or reconnecting the HO2S electrical connector.

1. Turn OFF the ignition.
2. Disconnect the HO2S electrical connector.
3. Inspect both halves of the connector for any signs of corrosion or contamination.

Did you find the condition?

--

Go to Step 19

Go to Step 6

6 |

1. Turn the ignition ON, with the engine OFF.
2. Using a test lamp connected to ground, probe the switched B+ circuit at the ECM side of the oxygen sensor connector.

Does the test lamp illuminate?

--

Go to Step 7

Go to Step 21

7 |

1. Turn OFF the ignition.
2. Connect a test lamp between the switched B+ circuit and the heater control circuit at the ECM side of the oxygen sensor connector.
3. Turn ON the ignition.

Does the test lamp illuminate?

--

Go to Step 8

Go to Step 9

8 |

1. Turn OFF the ignition.
2. Disconnect the ECM electrical connector C1.
3. With the test lamp still connected between the switched B+ and the control circuit, turn ON the ignition.

Does the test lamp illuminate?

--

Go to Step 20

Go to Step 25

9 |

1. Start and idle the engine.
2. Observe the test lamp.

Does the test lamp illuminate or flash?

--

Go to Step 10

Go to Step 15

10 |

1. Turn OFF the ignition.
2. Disconnect the test lamp.

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

3. Jumper the HO2S signal circuit to a known good ground.
4. Turn ON the ignition, with the engine OFF.
5. 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 11

Go to Step 14

11 |

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 23

Go to Step 12

12 |

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

Did you find and correct the condition?

--

Go to Step 26

Go to Step 13

13 | Measure the resistance from the ground stud at the ECM to battery ground. Is the resistance less than the specified value? | 5 ohms | Go to Step 24 | Go to Step 22
14 |

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 the circuit as necessary. Refer to Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 26

Go to Step 24

15 |

1. Turn OFF the ignition.
2. Disconnect the ECM connector C1.
3. Test the heater control circuit for an open, high resistance, or a short to voltage.
4. Repair the circuit as necessary. Refer to Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 26

Go to Step 24

16 |

1. Test the switched B+ circuit for a short to ground.
2. Repair as necessary. Refer to Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 26

Go to Diagnostic Aids

17 | Locate and repair the open in the B+ circuit from the engine controls power relay to the splice for the oxygen sensors. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 26 | --
18 | Repair the exhaust leak as necessary. Did you complete the repair? | -- | Go to Step 26 | --
19 | Repair or replace the terminal as necessary. Refer to Connector Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 26 | --
20 | Repair the short to ground in the heater control circuit. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 26 | --
21 | Repair the open in the B+ circuit from the splice to the oxygen sensor. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 26 | --
22 | Repair the high resistance in the ECM ground circuit. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 26 | --
23 | Replace the HO2S. Refer to Heated Oxygen Sensor Replacement . Did you complete the replacement? | -- | Go to Step 26 | --
24 |

1. Test for poor connections 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 26

Go to Step 25

25 | 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 26

--

26 |

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 27

Go to Step 2

27 | 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