GM Service Manual Online
For 1990-2009 cars only

Circuit Description

In order to control emissions, a 3-way catalytic converter converts any harmful exhaust emissions into harmless water vapor and carbon dioxide.

The powertrain control module (PCM) has the capability to monitor this process by using a rear heated oxygen sensor (HO2S 2). The HO2S 2 , located in the exhaust stream past the catalytic converter, produces an output signal which indicates the storage capacity of the catalyst. This in turn indicates the catalysts ability to convert the exhaust emissions effectively. If the catalyst is functioning properly, the HO2S 2 signal will be far less active than the signal produced by the front oxygen sensor (O2S 1).

Conditions for Running the DTC

    • DTCs P0105, P0107, P0108, P0112, P0113, P0117, P0118, P0122, P0123, P0171, P0201, P0202, P0203, P0204, P0300, P0301, P0302, P0303, P0304, P0335, P0440, P0442, P0446, P0506, P0507, P0601, P0602, or P1441 are not set.
    • The battery voltage is greater than 10 volts.
    • The fuel level is greater than 10 percent.
    • The engine run time is greater than 10 seconds.
    • The airflow is more than 5.5 g/s for 140 seconds.
    • The engine coolant temperature (ECT) is more than 40°C (104°F).
    • The throttle position (TP) is between 8-56 percent.
    • The manifold absolute pressure (MAP) is greater than 25 kPa.
    • The engine is operating in Closed Loop.

Conditions For Setting The DTC

HO2S 2 remains between 425-460 mV for 125 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.

Diagnostic Aids

An intermittent could be the result of the following conditions:

    • A poor electrical connection
    • Moisture in the electrical connector or in the wiring
    • Rubbed-through wire insulation
    • Broken wire inside the insulation

Check for the following conditions:

    • A poor electrical connection or a damaged harness--Inspect the PCM harness for an open in the HO2S 2 signal circuit. Check for the following conditions:
       - Improper mating
       - Broken locks
       - Improperly formed connectors
       - Damaged terminals
       - A poor terminal-to-wire connection
       - A damaged harness
    • Intermittent test--Observe the HO2S 2 on the scan tool while moving the related electrical connectors and the wiring harness with the ignition switch ON. If the malfunction is induced, the HO2S 2 display will change. This test should help to isolate the location of the malfunction.

Obstruction of the air reference and degraded HO2S 2 performance could result in any attempt to repair the HO2S harness or connector.

The HO2S 2 must have a clean air reference in order for the HO2S 2 to function properly. This clean air reference is obtained by way of the HO2S 2 wires.

Test Description

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

  1. After the ignition is turned ON, the HO2S heater heats up causing the HO2S signal voltage to either increase or decrease. This indicates that the HO2S heater is OK.

  2. If the HO2S voltage changes more than the specified value, the condition is not present.

  3. If the voltage is below the specified value, the high signal circuit, the low signal circuit, and the PCM are OK.

  4. If the voltage is above the specified value, the low signal circuit is OK.

  5. Resistance below the specified value indicates the HO2S heater is shorted.

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

Important: Allow the engine to cool for one-half hour before proceeding with this diagnostic. This allows the HO2S signal voltage to return to bias voltage, approximately 447 mV.

  1. Install a scan tool.
  2. Turn ON the ignition, with the engine OFF.
  3. Immediately observe the HO2S 2 voltage parameter with a scan tool for 2 minutes.

Does the HO2S 2 voltage change from bias voltage to more than or less than the specified range?

300-600 mV

Go to Step 3

Go to Step 5

3

  1. Start the engine.
  2. Allow the engine to reach operating temperature.
  3. Operate the engine at 2,000 RPM for 30 seconds.
  4. While observing the HO2S 2 voltage parameter with a scan tool, quickly cycle the throttle from closed throttle to wide open throttle, 3 times.

Did the HO2S 2 voltage change more than the specified value?

300 mV

Go to Step 4

Go to Step 5

4

  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 5

Go to Diagnostic Aids

5

  1. Disconnect the HO2S 2 connector.
  2. Turn ON the ignition, with the engine OFF.
  3. Connect a 3-amp fused jumper wire between the high signal circuit of the HO2S 2 on the engine harness side and a good ground.
  4. Connect a 3-amp fused jumper wire between the low signal circuit of the HO2S 2 on the engine harness side and a good ground.
  5. Observe the HO2S 2 voltage parameter with a scan tool.

Is the HO2S 2 voltage less than the specified value?

200 mV

Go to Step 9

Go to Step 6

6

  1. Remove both jumper wires from the HO2S 2 high signal and low signal circuits.
  2. Measure the voltage from the low signal circuit of the HO2S 2 on the engine harness side to a good ground with a DMM. Refer to Measuring Voltage in Wiring Systems.

Is the voltage more than the specified value?

4 V

Go to Step 7

Go to Step 8

7

Test the HO2S 2 high signal circuit for an open. Refer to Testing for Continuity and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 21

Go to Step 16

8

Test the HO2S 2 low signal circuit for an open. Refer to Testing for Continuity and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 21

Go to Step 16

9

  1. Remove both jumper wires from the HO2S 2 high signal and low signal circuits.
  2. Inspect the fuse that provides voltage to the HO2S 2 heater.

Is the fuse open?

--

Go to Step 12

Go to Step 10

10

  1. Turn ON the ignition, with the engine OFF.
  2. Probe the ignition voltage circuit of the HO2S 2 on the engine harness side with a test lamp that is connected to a good ground.

Does the test lamp illuminate?

--

Go to Step 11

Go to Step 17

11

Connect a test lamp between the ignition voltage circuit of the HO2S 2 on the engine harness side and the heater ground circuit of the HO2S 2 on the engine harness side.

Does the test lamp illuminate?

--

Go to Step 15

Go to Step 18

12

  1. Test the ignition voltage circuit of the HO2S 2 for a short to ground. Refer to Testing for Short to Ground and Wiring Repairs in Wiring Systems.
  2. Replace the fuse that provides voltage to the HO2S 2 Heater.

Did you find and correct a short to ground in the ignition voltage circuit?

--

Go to Step 21

Go to Step 13

13

Test the HO2S 2 ignition voltage circuit, sensor side, for a short to the HO2S Body. Refer to Testing for Continuity in Wiring Systems.

Did you find the condition?

--

Go to Step 19

Go to Step 14

14

Measure the resistance between the HO2S 2 ignition voltage circuit, sensor side, and the HO2S 2 heater ground circuit, sensor side with a DMM.

Does the resistance measure below the specified value?

3 ohms

Go to Step 19

Go to Diagnostic Aids

15

Inspect for poor connections at the harness connector of the HO2S 2. 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 21

Go to Step 19

16

Inspect for poor connections at 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 21

Go to Step 20

17

Repair the open in the HO2S 2 ignition voltage circuit. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

--

Go to Step 21

--

18

Repair the open in the HO2S 2 heater ground circuit. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

--

Go to Step 21

--

19

Replace the HO2S 2. Refer to Heated Oxygen Sensor Replacement .

Did you complete the replacement?

--

Go to Step 21

--

20

Replace the PCM. Refer to Powertrain Control Module Replacement .

Did you complete the replacement?

--

Go to Step 21

--

21

  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 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

System OK