For 1990-2009 cars

### Circuit Description

Heated oxygen sensors (HO2S) are used in order to minimize the amount of time required to enter Closed Loop fuel control operation and to allow accurate catalyst monitoring. The HO2S 1 heater is fed power directly from ignition 1. The HO2S 1 heater control circuit or heater ground is connected to the powertrain control module (PCM). The PCM controls HO2S heater operation by grounding the control circuit via an internal solid state device called a driver. The primary function of the driver is to supply the ground for the component being controlled. The driver for the HO2S 1 heater control circuit has the ability to measure the amount of current drawn by the controlled device.

### Conditions for Running the DTC

The engine is running.

### Conditions for Setting the DTC

• | The PCM detects that the heater control circuit current is greater than the capacity of the PCM internal driver.

• | Above condition is present for longer than 20 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 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.

### Test Description

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

1. Check the HO2S heater current with the engine at operating temperature, and allow time for the heater current to stabilize. The HO2S heater current is initially higher until the sensor reaches full operating temperature.

2. Ensures that the ignition 1 voltage circuit to the HO2S is not open or shorted. The test lamp should be connected to a good chassis ground in case the HO2S low reference or HO2S heater low control circuit is malfunctioning.

3. Checks the HO2S heater low control circuit. The engine must be running for the PCM to enable the heater.

4. Checks for a short to voltage in the HO2S heater control circuit.

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 |

1. Start the engine and allow the idle to stabilize for at least one minute. The engine should be at normal operating temperature.
2. Monitor the O2 Heater Current on the scan tool.

Is the O2 Heater Current within the specified range?

0.25-0.85 Amps

Go to Intermittent Conditions

Go to Step 3

3 | Inspect the fuse for the HO2S 1 ignition 1 voltage circuit. Is the fuse open? | -- | Go to Step 11 | Go to Step 4
4 |

1. Turn ON the ignition, with the engine OFF.
2. Disconnect the HO2S 1 electrical connector.

Important:: Use a known good ground. Do not use the HO2S 1 heater low control circuit or the HO2S 1 low reference circuit.

3. Use a test lamp connected to ground in order to probe the ignition 1 voltage circuit at the engine harness side of the HO2S.

Does the test lamp illuminate?

--

Go to Step 5

Go to Step 7

5 |

1. Connect a test lamp between the HO2S 1 ignition 1 voltage circuit and the HO2S 1 heater low control circuit.
2. Start the engine.

Does the test lamp illuminate?

--

Go to Step 9

Go to Step 6

6 |

1. Turn OFF the ignition.
2. Connect a test lamp between a good ground and HO2S 1 heater low control circuit.
3. Start the engine.

Does the test lamp illuminate?

--

Go to Step 8

Go to Step 12

7 | Repair the open in the ignition 1 voltage circuit to the HO2S 1. Refer to Heated Oxygen Sensor Wiring Repairs in Wiring Systems. Did you complete the action? | -- | Go to Step 14 | --
8 | Repair the short to voltage in the HO2S 1 heater low control circuit. Refer to Heated Oxygen Sensor Wiring Repairs in Wiring Systems. Did you complete the action? | -- | Go to Step 14 | --
9 |

1. Check for poor connections or poor terminal tension at the HO2S 1.
2. If a poor connection is found, replace the terminals. Refer to Heated Oxygen Sensor Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 14

Go to Step 10

10 | Replace HO2S 1. Refer to Heated Oxygen Sensor 1 Replacement in Wiring Systems. Did you complete the replacement? | -- | Go to Step 14 | --
11 | Locate and repair the short to ground in the HO2S 1 ignition 1 voltage circuit and replace the fuse. Refer to Heated Oxygen Sensor Wiring Repairs in Wiring Systems. Did you complete the action? | -- | Go to Step 14 | --
12 |

1. Check for poor connections or poor terminal tension at the PCM.
2. Refer to Testing for Intermittent Conditions and Poor Connections or Connector Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 14

Go to Step 13

13 | Replace the PCM. Refer to Powertrain Control Module Replacement . Did you complete the replacement? | -- | Go to Step 14 | --
14 |

1. Start the engine and allow the idle to stabilize for about one minute. The engine should be at a normal operating temperature.
2. Monitor the O2 Heater Current on the scan tool.

Does the scan tool indicate that the current is within the specified range?

0.25-0.85 Amps

Go to Step 15

Go to Step 2

15 |

1. Clear the DTCs using the scan tool.
2. 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