For 1990-2009 cars

### Circuit Description

Heated oxygen sensors (HO2S) are used for fuel control and post catalyst monitoring. Each HO2S compares the oxygen content of the surrounding air with the oxygen content in the exhaust stream. The HO2S must reach operating temperature to provide an accurate voltage signal. A heating element inside the HO2S minimizes the time required for the sensor to reach operating temperature. Voltage is provided to the heater by the ignition 1 voltage circuit through a fuse. With the engine running, ground is provided to the heater by the HO2S heater low control circuit, through a low side driver within the powertrain control module (PCM).

The PCM commands the heater ON or OFF to maintain a specific HO2S operating temperature range. The PCM monitors the voltage on the HO2S heater low control circuit for heater fault diagnosis. If the PCM detects that the HO2S heater low control circuit voltage is not within a specified range, DTC P0030 sets for HO2S 1, or DTC P0036 sets for HO2S 2.

### DTC Descriptors

This diagnostic procedure supports the following DTCs:

• | DTC P0030 HO2S Heater Control Circuit Sensor 1

• | DTC P0036 HO2S Heater Control Circuit Sensor 2

### Conditions for Running the DTC

• | The Ignition 1 Signal parameter is between 11-18 volts.

• | The Engine Speed is more than 425 RPM.

• | DTC P0030 or P0036 runs continuously when the above conditions are met.

### Conditions for Setting the DTC

• | The PCM detects that the affected HO2S heater low control circuit is not within a specified range.

• | DTC P0030 or P0036 sets within 60 seconds when the above condition is met.

### 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.

Step | Action | Value(s) | Yes | No
--- | --- | --- | --- | ---
Schematic Reference: Engine Controls Schematics Connector End View Reference: Powertrain 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. Wait 15 seconds to allow the heated oxygen sensor (HO2S) heater current to stabilize.
3. Observe the affected HO2S heater current parameter with a scan tool.

Is the HO2S heater current parameter within the specified range?

0.2-3.0 A

Go to Step 3

Go to Step 4

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 Intermittent Conditions

4 |

1. Turn OFF the ignition.
2. Inspect the O2 sensor fuse.

Is the O2 sensor fuse open?

--

Go to Step 5

Go to Step 6

5 | Test the ignition 1 voltage circuit for a short to ground. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | -- | Go to Step 18 | Go to Step 8
6 |

1. Disconnect the affected HO2S.
2. Turn ON the ignition, with the engine OFF.
3. Probe the ignition 1 voltage circuit of the HO2S harness connector on the engine harness side with a test lamp that is connected to a good ground. Refer to Probing Electrical Connectors .

Does the test lamp illuminate?

--

Go to Step 7

Go to Step 15

7 |

1. Turn OFF the ignition.
2. Probe the HO2S heater low control circuit of the HO2S harness connector on the engine harness side with a test lamp connected to battery voltage.
3. With the ignition still OFF, observe the test lamp.

Does the test lamp illuminate?

--

Go to Step 10

Go to Step 9

8 | Test the ignition 1 voltage circuit on the sensor side of the HO2S 1 connector for a short to ground. Refer to Circuit Testing . Is the sensor shorted to ground? | -- | Go to Step 16 | Go to Intermittent Conditions
9 | Start the engine with the test lamp still connected from the previous step. Is the test lamp ON steady or blinking? | -- | Go to Step 13 | Go to Step 11
10 | Test the HO2S heater low control circuit for a short to ground. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | -- | Go to Step 18 | Go to Step 14
11 | Test the HO2S heater low control circuit for a short to voltage. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | -- | Go to Step 18 | Go to Step 12
12 | Test the HO2S heater low control circuit for an open or for high resistance. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | -- | Go to Step 18 | Go to Step 14
13 | Test for shorted terminals and for 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 18 | Go to Step 16
14 | Test for shorted terminals and for poor connections at the powertrain control module (PCM). Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs . Did you find and correct the condition? | -- | Go to Step 18 | Go to Step 17
15 | Repair the open or high resistance in the ignition 1 voltage circuit. Refer to Wiring Repairs . Did you complete the repair? | -- | Go to Step 18 | --
16 | Notice: Refer to Heated Oxygen Sensor Resistance Learn Reset Notice in the Preface section. Replace the affected HO2S. Refer to Heated Oxygen Sensor 1 Replacement or Heated Oxygen Sensor 2 Replacement . Did you complete the replacement? | -- | Go to Step 18 | --
17 | Replace the PCM. Refer to Control Module References for replacement, setup, and programming. Did you complete the replacement? | -- | Go to Step 18 | --
18 |

1. Replace the O2 sensor fuse if necessary.
2. Clear the DTCs with a scan tool.
3. Turn OFF the ignition for 30 seconds.
4. Start the engine.
5. 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 19

19 | 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