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. If the ECM detects the control circuit voltage is within a predetermined range when the circuit is commanded OFF, this DTC sets.

### DTC Descriptors

This diagnostic procedure supports the following DTCs:

• | DTC P0030 HO2S Heater Control Circuit Bank 1 Sensor 1

• | DTC P0036 HO2S Heater Control Circuit Bank 1 Sensor 2

• | DTC P0050 HO2S Heater Control Circuit Bank 2 Sensor 1

• | DTC P0056 HO2S Heater Control Circuit Bank 2 Sensor 2

### Conditions for Running the DTC

#### P0030 and P0050

• | Engine is running.

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

• | The ECM has commanded the heated oxygen sensor (HO2S) heater ON and OFF at least once during the ignition cycle.

• | DTC P0030, P0050 run continuously once the above conditions are met.

#### P0036 and P0056

• | The engine speed is more than 80 RPM.

• | The ignition 1 voltage is between 10-18 volts.

• | Rear HO2S heater is ready.

• | Rear HO2S is near to frost state.

• | The ECM has commanded the HO2S heater ON and OFF at least once during the ignition cycle.

• | DTC P0036, P0056 run continuously once the above conditions are met.

### Conditions for Setting the DTC

• | The ECM detects an open in the heater circuits of the HO2S when the heater is commanded OFF.

• | 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 malfunction indicator lamp (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 Engine Controls Component Views .

• | If the condition is intermittent, move the related harnesses and connectors, with the engine operating, while monitoring the circuit status for the component with a scan tool. The circuit status parameter changes from OK or Indeterminate to Fault if there is a condition with the circuit or a connection. The ODM information is in the output driver module (ODM) data list.

• | 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.

• | Inspect the sensor pigtail or the harness for contacting the exhaust system.

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

### Test Description

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

1. If both DTCs are set for either the front sensors or the rear sensors, the ignition voltage circuit to the heaters may be open. The front sensors are fused separately from the rear sensors.

2. The engine must be running for the ECM to operate the control circuit.

3. The heater control circuit is equipped with a feedback circuit internal to the ECM. This feedback circuit allows the ECM to determine if the heater control circuit is open, shorted to ground, or shorted to a voltage. If the voltage is not within the specified range, there is a condition with the control circuit.

#### DTC P0030, DTC P0036, DTC P0050, or DTC P0056 - HO2S Heater Control Circuit (Open)

Step | Action | Values | Yes | No
--- | --- | --- | --- | ---
Schematic Reference: Engine Controls Schematics Connector End View Reference: Engine Control Module Connector End Views or Engine Controls Connector End Views
1 | Did you perform the Diagnostic System Check - Vehicle? | -- | Go to Step 2 | Go to Diagnostic System Check - Vehicle
2 |

1. Start the engine.
2. Allow the engine to idle for at least 30 seconds.
3. Observe the DTC information with a scan tool.

Does DTC P0030, DTC P0036, DTC P0050, or DTC P0056 set?

--

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 | Are DTCs P0030 and P0050 set at the same time or are DTCs P0036 and P0056 set at the same time? | -- | Go to Step 11 | Go to Step 5
5 |

1. Turn OFF the ignition.

Important: The ignition must be OFF when disconnecting or connecting the heated oxygen sensor (HO2S) electrical connector.

2. Disconnect the appropriate HO2S.
3. Connect a test lamp between the ignition voltage circuit of the HO2S and the heater control circuit of the HO2S.
4. Start the engine.

Does the test lamp illuminate or flash?

--

Go to Step 6

Go to Step 7

6 |

1. Turn the ignition switch to ON position, with the engine OFF.
2. Measure the voltage between the heater control circuit of the HO2S and the engine control module (ECM) housing with a DMM.

Is the voltage within the specified range?

4.6-5.2 V

Go to Step 9

Go to Step 10

7 | Connect a test lamp between the ignition 1 voltage circuit of the HO2S and the ECM housing. Does the test lamp illuminate? | -- | Go to Step 8 | Go to Step 11
8 |

1. Turn OFF the ignition.
2. Disconnect the ECM.
3. Test the heater control circuit between the HO2S and the ECM for an open or high resistance. Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

--

Go to Step 14

Go to Step 10

9 | Test for an intermittent and for a poor connection 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 14 | Go to Step 12
10 | Test for an intermittent and for a poor connection 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 14 | Go to Step 13
11 |

Important: The ignition voltage circuit supplies voltage to other components. Make sure you test all circuits for a short to ground or test all components for being shorted that share the ignition voltage circuit.

1. Repair the open or the grounded ignition voltage circuit of the HO2S. Refer to Wiring Repairs .
2. Replace the fuse if necessary.

Did you complete the repair?

--

Go to Step 14

--

12 | Replace the HO2S. Refer to the appropriate procedure:

• | Heated Oxygen Sensor Replacement - Bank 1 Sensor 1

• | Heated Oxygen Sensor Replacement - Bank 1 Sensor 2

• | Heated Oxygen Sensor Replacement - Bank 2 Sensor 1

• | Heated Oxygen Sensor Replacement - Bank 2 Sensor 2

Did you complete the replacement?

--

Go to Step 14

--

13 | Replace the ECM. Refer to Control Module References for replacement, setup, and programming. Did you complete the replacement? | -- | Go to Step 14 | --
14 |

1. Clear any 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 15

15 | 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