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 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 engine control module (ECM).

The ECM commands the heater ON or OFF to maintain a specific HO2S operating temperature range. The ECM monitors the voltage on the HO2S heater low control circuit for heater fault diagnosis. If the ECM detects that the HO2S heater low control circuit voltage is not within a specified range, DTC P0030 sets for HO2S sensor 1, DTC P0036 sets for HO2S sensor 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.
    • This diagnostic runs continuously when the above conditions are met.

Conditions for Setting the DTC

The ECM detects that the affected HO2S heater low control circuit is not within a specified range for 0.25 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.

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

Is DTC P0030 set?

--

Go to Step 4

Go to Step 3

3

  1. Start the engine.
  2. Wait one minute 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?

0.25-1.375 A

Go to Step 5

Go to Step 6

4

  1. Start the engine.
  2. Wait one minute to allow the 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?

0.25-3.125 A

Go to Step 5

Go to Step 6

5

  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 6

Go to Testing for Intermittent Conditions and Poor Connections

6

  1. Turn OFF the ignition.
  2. Inspect the fuse that supplies the applicable HO2S heater.

Is the fuse open?

--

Go to Step 7

Go to Step 8

7

Test the ignition 1 voltage circuit for a short to ground. Refer to the following procedures:

    •  Circuit Testing
    •  Wiring Repairs

Did you find and correct the condition?

--

Go to Step 21

Go to Step 10

8

  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 9

Go to Step 18

9

  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 12

Go to Step 11

10

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 19

Go to Testing for Intermittent Conditions and Poor Connections

11

Start the engine with the test lamp still connected from the previous step.

Is the test lamp ON steady or blinking?

--

Go to Step 15

Go to Step 13

12

Test the HO2S heater low control circuit for a short to ground. Refer to the following procedures:

    •  Circuit Testing
    •  Wiring Repairs

Did you find and correct the condition?

--

Go to Step 21

Go to Step 17

13

Test the HO2S heater low control circuit for a short to voltage. Refer to the following procedures:

    •  Circuit Testing
    •  Wiring Repairs

Did you find and correct the condition?

--

Go to Step 21

Go to Step 14

14

Test the HO2S heater low control circuit for an open or for high resistance. Refer to the following procedures:

    •  Circuit Testing
    •  Wiring Repairs

Did you find and correct the condition?

--

Go to Step 21

Go to Step 17

15

Measure the resistance of the following circuits with a DMM:

    • The HO2S heater low control circuit
    • The ignition 1 voltage circuit

Refer to Circuit Testing .

Is the resistance of either circuit more than the specified value?

3 ohms

Go to Step 18

Go to Step 16

16

Test for shorted terminals and for poor connections at the HO2S. Refer to the following procedures:

    •  Connector Repairs

Did you find and correct the condition?

--

Go to Step 20

Go to Step 19

17

Test for shorted terminals and for poor connections at the engine control module (ECM). Refer to the following procedures:

    •  Connector Repairs

Did you find and correct the condition?

--

Go to Step 21

Go to Step 20

18

Repair the open or high resistance in the circuit. Refer to Wiring Repairs and Heated Oxygen Sensor Wiring Repairs .

Did you complete the repair?

--

Go to Step 21

--

19

Replace the affected HO2S. Refer to the appropriate procedure:

Did you complete the replacement?

--

Go to Step 21

--

20

Replace the ECM. Refer to Control Module References for replacement, setup, and programming.

Did you complete the replacement?

--

Go to Step 21

--

21

  1. Replace the 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 22

22

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