GM Service Manual Online
For 1990-2009 cars only

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 of the exhaust stream. When the vehicle is first started, the powertrain control module (PCM) operates in an Open Loop mode, ignoring the HO2S signal voltage when calculating the air-to-fuel ratio. The PCM supplies the HO2S with a reference, or bias, voltage of about 450 mV. The HO2S generates a voltage within a range of 0-1,000 mV that fluctuates above and below bias voltage once in Closed Loop. A high HO2S voltage output indicates a rich fuel mixture. A low HO2S voltage output indicates a lean mixture. Heating elements inside the HO2S minimize the time required for the sensors to reach operating temperature, and to provide an accurate voltage signal. The PCM controls the HO2S 1 heater low control circuit with a low side driver. The HO2S 1 heater diagnostic monitors the current draw through the HO2S 1 low side driver when the engine is running. If the PCM detects that the HO2S 1 heater low control circuit current level is not within the calibrated range, DTC P0135 will set.

The HO2S 1 has the following circuits:

    • A HO2S 1 high signal circuit
    • A HO2S 1 low reference circuit
    • A HO2S 1 heater ignition voltage circuit
    • A HO2S 1 heater low control circuit
    • A low reference loop circuit

Conditions for Running the DTC

    • DTCs P0101, P0102, P0103, P0107, P0108, P0112, P0113, P0116, P0117, P0118, P0121, P0122, P0123, P0125, P0128, P0201-P0206, P0410, P0440, P0442, P0443, P0446, P0449, P1441 are not set.
    •  The Engine Run Time parameter is more than 3 minutes.
    • The ECT Sensor parameter is more than 65°C (158°F).
    • The Engine Speed parameter is between 650-2,500 RPM.
    • The MAF Sensor parameter is between 4-26 g/s.
    • The system voltage is between 9-18 volts.

Conditions for Setting the DTC

The PCM detects that the 02 Heater Current parameter is less than 0.25 A or more than 0.90 A.

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

Values

Yes

No

Schematic Reference: Engine Controls Schematics

Connector End View Reference: Engine Controls Connector End Views or Powertrain Control Module Connector End Views

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.
  2. Allow the engine to idle at operating temperature. Refer to Scan Tool Data List .
  3. Observe the heated oxygen sensor (HO2S) 1 Heater Current parameter with a scan tool.
  4. Allow the HO2S 1 Heater Current parameter to stabilize.

Is the amperage within the specified range?

0.25-0.85 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

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

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

Does the test lamp illuminate?

--

Go to Step 6

Go to Step 5

5

Test the HO2S 1 heater ignition 1 voltage fuse for an open. Refer to Circuit Testing in Wiring Systems.

Is the fuse open?

--

Go to Step 10

Go to Step 15

6

  1. Turn OFF the ignition.
  2. Connect a test lamp between the HO2S ignition 1 voltage circuit and the HO2S heater low control circuit on the engine harness side connector.
  3. Start the engine.

Does the test lamp illuminate?

--

Go to Step 7

Go to Step 8

7

  1. Leave the test lamp connected between the HO2S 1 heater ignition voltage circuit and the HO2S 1 heater low control circuit.
  2. Turn OFF the ignition.
  3. Turn ON the ignition, with the engine OFF.

Does the test lamp illuminate?

--

Go to Step 9

Go to Step 12

8

  1. Turn OFF the ignition.
  2. Disconnect the powertrain control module (PCM) connector containing the HO2S 1 heater low control circuit.
  3. Measure the resistance from the HO2S heater low control circuit between the PCM harness connector and the HO2S harness connector using a DMM. Refer to Circuit Testing in Wiring Systems.

Is the resistance within the specified range?

0-5 ohms

Go to Step 13

Go to Step 14

9

Test the HO2S 1 heater low control circuit for a short to ground. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 18

Go to Step 13

10

Test the HO2S 1 heater ignition voltage circuit for a short to ground and replace the fuse. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 18

Go to Step 11

11

Measure the resistance from the HO2S ignition 1 voltage circuit, on the sensor side of the HO2S harness connector, to each of the following circuits:

    • The HO2S low reference circuit
    • Ground

Is the resistance less than the specified value?

5ohms

Go to Step 16

Go to Intermittent Conditions

12

Test for an intermittent and for a poor connection at the harness connector of the HO2S 1. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 18

Go to Step 16

13

Test for an intermittent and for a poor connection at the harness connector of the PCM. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 18

Go to Step 17

14

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

Did you complete the repair?

--

Go to Step 18

--

15

Repair the open or high resistance in the HO2S ignition 1 voltage circuit. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

--

Go to Step 18

--

16

Replace the HO2S 1. Refer to Heated Oxygen Sensor 1 Replacement .

Did you complete the replacement?

--

Go to Step 18

--

17

Replace the PCM. Refer to Powertrain Control Module Replacement .

Did you complete the replacement?

--

Go to Step 18

--

18

  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 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

System OK