For 1990-2009 cars

### Circuit Description

The heated oxygen sensor (HO2S) heater 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, ignition voltage is supplied directly to the sensor heater. The engine control module (ECM) controls the heater operation by first modulating the control circuit to ground when the sensors are cold. This prevents the possibility of thermal shock to the sensor, from condensation build-up on the sensor, by controlling the sensor's rate of heating. After a predetermined amount of time, the ECM commands the heaters ON continuously. Once the sensor reaches operating temperature, the ECM may modulate the heater control circuit to ground to maintain a desired temperature.

The ECM controls the heater by grounding the control circuit with a solid state device called a driver. The driver is equipped with a feedback circuit that is pulled up to a voltage. The ECM can determine if a control circuit is open, shorted to ground, or shorted to a voltage by monitoring the feedback voltage.

The ECM measures the internal resistance of the sensing element to determine if there is an HO2S condition. If the internal resistance is too high, this DTC sets.

### DTC Descriptors

This diagnostic procedure supports the following DTCs:

• | DTC P0141 HO2S Heater Performance Bank 1 Sensor 2

• | DTC P0161 HO2S Heater Performance Bank 2 Sensor 2

### Conditions for Running the DTC

• | Before the ECM can report DTC P0141 or P0161 failed, DTCs P0036, P0037, P0038, P0056, P0057, and P0058 must run and pass.

• | DTCs P0137, P0138, P0140, P0157, P0158, or P0160 are not set.

• | The engine is running.

• | The ignition 1 voltage is between 10.5-18 volts.

• | The ECM detects that the rear HO2S internal sensing element resistance is valid.

• | The fuel system is not in a decel fuel shut-off.

• | The intake air temperature is more than -30°C (-22°F).

• | If the engine is operating and then the ignition is turned OFF, the engine must be OFF for at least 2 minutes before the next start-up for the diagnostic to run.

• | The calculated exhaust temperature of the rear HO2S is between 360-500°C (680-932°F).

• | The ECM detects that the rear HO2S circuit does not break.

• | The ECM detects that the rear HO2S inactive state lasts for at least 120 seconds, the ECM supplies power continuously.

• | DTC P0141 and P0161 run continuously once the above conditions are met for approximately 100 seconds.

### Conditions for Setting the DTC

• | The ECM detects that the HO2S internal resistance is not within the normal range for more than 6 seconds.

• | The condition exists for more than 4 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 MIL after 4 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-A/BT-8637 Connector Test Adapter Kit for any test that requires probing the ECM harness connector or a component harness connector.

• | The lower connector of the ECM is connector C1 and the upper connector of the ECM is connector C2. Refer to Front of Vehicle/Engine Compartment Component Views.

• | The rear HO2S will not go into Closed Loop when the engine is idling. Once the HO2S are at operating temperature, and the vehicle is moving, the HO2S will go into Closed Loop.

• | For an intermittent condition, refer to Intermittent Conditions.

### Test Description

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

1. This step determines if the condition exists.

2. This step tests the signal circuit of the HO2S for high resistance.

Step | Action | Values | Yes | No
--- | --- | --- | --- | ---
Schematic Reference: Engine Controls Schematics Connector End View Reference: Component Connector End Views
1 | Did you perform the Diagnostic System Check - Vehicle? | -- | Go to Step 2 | Go to Diagnostic System Check - Vehicle
2 | Note: DTC P0141 is for bank 1 sensor 2 and DTC P0161 is for bank 2 sensor 2.

1. Allow the engine to reach operating temperature.
2. Operate the vehicle within the parameters specified in Conditions for Running the DTC.
3. Observe the DTC information with a scan tool.

Did DTC P0141 or DTC P0161 fail this ignition?

--

Go to Step 4

Go to Step 3

3 |

1. Observe the Freeze Frame/Failure Records for this DTC.
2. Turn OFF the ignition for 30 seconds.
3. Start the engine.
4. Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records.

Did the DTC fail this ignition?

--

Go to Step 4

Go to Diagnostic Aids

4 |

1. Turn OFF the ignition.
2. Disconnect the heated oxygen sensor (HO2S).
3. Connect a 3-amp fused jumper wire between the signal circuit of the HO2S and a good ground.
4. Turn the ignition switch to ON position, with the engine OFF.
5. Observe the HO2S voltage parameter with a scan tool.

Is the voltage less than the specified value?

25 mV

Go to Step 5

Go to Step 8

5 |

1. Connect a 3-amp fused jumper wire between the signal circuit and the low reference circuit of the HO2S.
2. Observe the HO2S voltage parameter with a scan tool.

Is the voltage less than the specified value?

25 mV

Go to Step 6

Go to Step 9

6 |

Note: Use the J 35616-200 Test Lamp Kit for this test. If the J 35616-200 is not available, use a test lamp that measures more than 20 ohms.

1. Connect a test lamp between the ignition 1 voltage circuit of the HO2S and a good ground.
2. Measure the voltage between the probe of the test lamp and a good ground with a DMM. Refer to Measuring Voltage Drop.

Is the voltage at the specified value?

B+

Go to Step 7

Go to Step 12

7 |

1. Disconnect the ECM.
2. Measure the resistance of the heater control circuit of the HO2S, with a DMM.

Is the resistance less than the specified value?

5 Ω

Go to Step 10

Go to Step 13

8 | Test the signal circuit of the HO2S for an open or for high resistance. Refer to Circuit Testing and Wiring Repairs. Did you find and correct the condition? | -- | Go to Step 16 | Go to Step 11
9 | Test the low reference circuit of the HO2S for an open or for high resistance. Refer to Circuit Testing and Wiring Repairs. Did you find and correct the condition? | -- | Go to Step 16 | Go to Step 11
10 | Test for shorted terminals and poor connections at the HO2S. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs. Did you find and correct the condition? | -- | Go to Step 16 | Go to Step 14
11 | Test for shorted terminals and poor connections at the ECM. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs. Did you find and correct the condition? | -- | Go to Step 16 | Go to Step 15
12 | Repair the open or the high resistance in the ignition 1 voltage circuit of the HO2S heater. Refer to Wiring Repairs. Did you complete the repair? | -- | Go to Step 16 | --
13 | Repair the open or the high resistance in the heater control circuit of the HO2S. Refer to Wiring Repairs. Did you complete the repair? | -- | Go to Step 16 | --
14 | Replace the HO2S. Refer to the appropriate procedure:

• | Heated Oxygen Sensor Replacement - Bank 1 Sensor 2

• | Heated Oxygen Sensor Replacement - Bank 2 Sensor 2

Did you complete the replacement?

--

Go to Step 16

--

15 | Replace the ECM. Refer to Control Module References for replacement, setup, and programming. Did you complete the replacement? | -- | Go to Step 16 | --
16 |

1. Clear the DTCs with a scan tool.
2. Turn OFF the ignition for 30 seconds.
3. Start the engine.
4. Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records.

Did the DTC fail this ignition?

--

Go to Step 2

Go to Step 17

17 | Observe the Capture Info with a scan tool. Are there any DTCs that have not been diagnosed? | -- | Go to Diagnostic Trouble Code (DTC) List - Vehicle | System OK