GM Service Manual Online
For 1990-2009 cars only

Circuit Description

The secondary heated oxygen sensor (HO2S) measures the oxygen content of the exhaust downstream of the three-way catalyst (TWC), so that the TWC efficiency is optimized. The powertrain control module (PCM) supplies a voltage near 450 mV between the HO2S high signal circuit and the low reference circuit. The HO2S varies the voltage over a range from about 1,000 mV when the exhaust is rich, down through about 10 mV when the exhaust is lean.

The PCM monitors and stores the HO2S voltage information. The PCM evaluates the HO2S voltage samples in order to determine the amount of time that the HO2S voltage was out of range. The PCM compares the stored HO2S voltage samples taken within each sample period and determines if the majority of the samples are out of the operating range.

The PCM monitors the HO2S voltage and detects when the voltage goes out of the bias range. If the PCM does not detect the voltage went out of the bias range, this DTC sets.

DTC Descriptors

This diagnostic procedure supports the following DTCs:

    • DTC P0139 HO2S Slow Response Bank 1 Sensor 2
    • DTC P0159 HO2S Slow Response Bank 2 Sensor 2

Conditions for Running the DTC

    • DTCs P0030, P0107, P0108, P0112, P0113, P0117, P0118, P0133, P0135, P0137, P0138, P0141, P0153, P0155, P0157, P0158, P0161, P0171, P0172, P0300, P0301, P0302, P0303, P0304, P0305, P0306, P0335, P0401, P0404, P0443, P0496, P1128, P1129, P2270, P2271, P2272, P2273, P2413, and P2414, are not set.
    • The engine has been running for at least 2 minutes.
    • The engine speed is between 1,000-2,400 RPM.
    • The engine coolant (ECT) temperature is at least 69°C (156°F).
    • The intake air (IAT) temperature is at least -18°C (0°F).
    • The HO2S 1 same bank lambda is between 0.73-1.47.
    • The vehicle speed is more than 48 km/h (30 mph)
    • The engine is in closed loop.
    • DTCs P0139 and P0159 run once per drive cycle when the above conditions are met.

Conditions for Setting the DTC

The HO2S 2 output voltage is between 0.29-0.75 volt for 30 seconds.

Action Taken When the DTC Sets

    • The PCM illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
    • The PCM records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the PCM stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the PCM records the operating conditions at the time of the failure. The PCM writes the conditions to the Freeze Frame and updates the Failure Records.

Conditions for Clearing the MIL/DTC

    • The PCM turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
    • A last test failed, or current DTC, clears when the diagnostic runs and does not fail.
    • A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
    • Use a scan tool in order to clear the MIL and the DTC.

Diagnostic Aids

    • An oxygen supply inside the HO2S is necessary for proper operation. The HO2S wires provide the supply of oxygen. Inspect the HO2S wires and connections for breaks or contamination. Refer to Wiring Repairs .
    • For an intermittent condition, refer to Intermittent Conditions .

Test Description

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

  1. The engine must be at the normal operating temperature before performing this test.

  2. If the scan tool indicates the HO2S voltage goes below 100 mV, this indicates the HO2S circuits and the PCM are OK.

  3. This step isolates the condition. Test the HO2S low reference circuit for an open or a high resistance, if the observed voltage is less than 100 mV.

Step

Action

Values

Yes

No

Schematic Reference: Engine Controls Schematics

Connector End View Reference: Powertrain 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

Important: 

   • DTC P0139 is for bank 1 sensor 2 and DTC P0159 is for bank 2 sensor 2.
   • Ensure the HO2S is secure before proceeding with this DTC. A loose sensor could cause this DTC to set.

  1. Allow the engine to reach operating temperature.
  2. Operate the engine above 1,200 RPM for 2 minutes.
  3. Observe the appropriate HO2S 2 voltage parameter with a scan tool.

Is the voltage at the specified value?

1,200 mV

Go to Step 4

Go to Step 3

3

  1. Observe the Freeze Frame and/or the Failure records data for this DTC.
  2. Turn the ignition OFF 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 and/or the Failure records data.

Did the DTC fail this ignition?

--

Go to Step 4

Go to Diagnostic Aids

4

  1. Turn OFF the ignition.
  2. Disconnect the appropriate heated oxygen sensor (HO2S) 2.
  3. Turn ON the ignition, with the engine OFF.
  4. Connect a 3-amp fused jumper wire between the HO2S signal circuit and the low reference circuit.
  5. Observe the HO2S 2 voltage parameter with a scan tool.

Is the HO2S voltage less than specified value?

100 mV

Go to Step 8

Go to Step 5

5

  1. Connect the fused jumper wire between the HO2S signal circuit and a good ground.
  2. Observe the HO2S voltage parameter with a scan tool.

Is the voltage less than the specified value?

100 mV

Go to Step 7

Go to Step 6

6

Test the signal circuit of the HO2S for an open or a high resistance. Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

--

Go to Step 12

Go to Step 9

7

Test the low reference circuit of the HO2S for an open or high resistance. Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

--

Go to Step 12

Go to Step 9

8

Test for an intermittent and for a poor connection at the HO2S. Refer to Testing for Intermittent Conditions and Poor Connections and Wiring Repairs .

Did you find and correct the condition?

--

Go to Step 12

Go to Step 10

9

Test for an intermittent and for a poor connection at the powertrain control module (PCM). Refer to Testing for Intermittent Conditions and Poor Connections and Wiring Repairs .

Did you find and correct the condition?

--

Go to Step 12

Go to Step 11

10

Replace the appropriate HO2S. Refer to the appropriate procedure:

Did you complete the replacement?

--

Go to Step 12

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11

  1. Replace the PCM. Refer to Control Module References for replacement, setup, and programming.
  2. Perform the idle learn procedure. Refer to Idle Learn .

Did you complete the replacement?

--

Go to Step 12

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12

  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 13

13

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