GM Service Manual Online
For 1990-2009 cars only

Circuit Description

Heated oxygen sensors (HO2S) are used 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

There are no active DTCs of any of the following types present:

    • DTCs P0101, P0102, P0103, P0107, P0108, P0112, P0113, P0117, P0118, P0121, P0122, P0123, P0125, P0128, P0201, P0202-P0206, P0410, P0440, P0442, P0443, P0446, P0449, or P1441 are not set.
    • The ignition voltage is more than 9 volts and less than 18 volts.
    • The engine run time is more than 4 minutes.
    • The engine coolant temperature (ECT) is more than 70°C (158°F).
    • The engine RPM is between 650-2,500 RPM.
    • The air flow is between 4-26 g/s.

Conditions for Setting the DTC

The HO2S 1 Heater Current is not within the calibrated range.

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 O2 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. This step 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. This step checks the HO2S heater ground circuit. The engine must be running for the PCM to enable the heater.

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 about one minute. The engine should be at normal operating temperature.
  2. Monitor the O2 Heater Current on the scan tool.

Does the scan tool indicate that the O2 Heater Current is within the specified range?

0.25-0.85 A

Go to Intermittent Conditions

Go to Step 3

3

Inspect the fuse for the HO2S ignition 1 voltage circuit.

Is the fuse open?

--

Go to Step 13

Go to Step 4

4

  1. Turn ON the ignition, with the engine OFF.
  2. Disconnect the HO2S 1 electrical connector.
  3. Important: Use a known good ground. Do not use the HO2S 1 heater low control circuit or the HO2S 1 low reference circuit.

  4. Probe the ignition 1 voltage circuit at the HO2S 1 electrical connector (PCM harness side) with a test lamp connected to ground.

Does the test lamp illuminate?

--

Go to Step 5

Go to Step 8

5

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

Does the test lamp illuminate?

--

Go to Step 6

Go to Step 7

6

  1. Turn OFF the ignition.
  2. Turn ON the ignition, with the engine OFF.

Does the test lamp illuminate?

--

Go to Step 10

Go to Step 11

7

  1. Turn OFF the ignition.
  2. Disconnect the PCM.
  3. Measure the resistance of the HO2S heater low control circuit between the PCM harness connector and the HO2S harness connector using a DMM.

Is the resistance within the specified range?

0-5 ohms

Go to Step 14

Go to Step 9

8

Repair the open HO2S ignition 1 voltage circuit to HO2S. Refer to Heated Oxygen Sensor Wiring Repairs in Wiring Systems.

Is the action complete?

--

Go to Step 16

--

9

Repair the open or high resistance in the HO2S 1 heater low control circuit. Refer to Heated Oxygen Sensor Wiring Repairs in Wiring Systems.

Is the action complete?

--

Go to Step 16

--

10

Repair a short to ground in the HO2S 1 heater low control circuit. Refer to Heated Oxygen Sensor Wiring Repairs in Wiring Systems.

Is the action complete?

--

Go to Step 16

Go to Step 14

11

  1. Check for poor connections or poor terminal tension at 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 16

Go to Step 12

12

Replace the HO2S 1. Refer to Heated Oxygen Sensor 1 Replacement in Wiring Systems.

Did you complete the replacement?

--

Go to Step 16

--

13

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 repair?

--

Go to Step 16

--

14

  1. Check for poor connections or 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 16

Go to Step 15

15

Replace the PCM. Refer to Powertrain Control Module Replacement .

Did you complete the replacement?

--

Go to Step 16

--

16

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

Is O2 Heater Current within the specified range?

0.25-0.85 A

Go to Step 17

Go to Step 2

17

  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 18

Go to Step 2

18

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