GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2001 🢒 Alero Export 🢒 Engine 🢒 Engine Controls - 3.4L 🢒 DTC P0140

Circuit Description

The powertrain control module (PCM) supplies a bias voltage of about 450 mV between the heated oxygen sensor (HO2S) signal circuit and the HO2S low signal circuit. When measured with a 10-megohm digital voltmeter, this voltage may display as low as 350 mV. The oxygen sensor signal varies from about 800 mV when the exhaust is rich, to about 50 mV when the exhaust is lean. The PCM constantly monitors the HO2S signal during Closed Loop operation. The PCM then compensates for a rich or lean condition by decreasing or increasing the injector pulse width as necessary. If the HO2S 2 voltage remains at or near the 450 mV bias for an extended time, DTC P0140 will set.

Conditions for Running the DTC
    • DTCs P0101, P0102, P0103, P0107, P0108, P0112, P0113, P0117, P0118, P0121, P0122, P0123, P0125, P0128, P0201-P0206, P0410, P0440, P0442, P0443, P0446, P0449, or P1441 are not set.
    • The engine has been running for at least 4 minutes.

Conditions for Setting the DTC
    • The HO2S 2 signal voltage remains between 412-500 mV for up to 90 seconds.
    • The ignition voltage should be more than 9 volts and less than 18 volts.
    • The test only runs once per trip.
    • A throttle position (TP) sensor change of more than 8 percent at least twice during the test.

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. This step checks for the correct sensor activity. When in Closed Loop fuel control, the HO2S voltage should rapidly swing above and below the bias voltage.

    2.

  2. This step checks for correct HO2S heater circuit operation up to the HO2S connector.

Step

Action

Values

Yes

No

1

Did you perform the Diagnostic System Check-Engine Controls?

--

Go to Step 2

Go to Diagnostic System Check - Engine Controls

2

  1. Engine at operating temperature.
  2. Operate the engine above 1,200 RPM for 2 minutes while monitoring HO2S 2 voltage on the scan tool.

Does the voltage vary outside the specified values?

412-500 mV

Go to Step 3

Go to Step 4

3
  1. Turn ON the ignition, with the engine OFF.
  2. Review and record scan tool Failure Records data.
  3. Operate the vehicle within Failure Records conditions.
  4. With a scan tool, observe Specific DTC info for DTC P0140 until the DTC P0140 test runs.

Does the DTC reset?

--

Go to Step 4

Go to Intermittent Conditions

4
  1. Turn ON the ignition, with the engine OFF.
  2. Disconnect HO2S 2 and jumper the HO2S high signal and low signal circuits (PCM side) to ground.
  3. Using a scan tool, monitor HO2S 2 voltage.

Does the voltage measure less than the specified value?

150 mV

Go to Step 8

Go to Step 5

5
  1. Remove the jumper wire from the HO2S high signal circuit, and leave the HO2S low signal circuit jumpered to ground.
  2. Using a DMM, measure voltage between the HO2S 2 high signal circuit (PCM side) and the HO2S 2 heater ground circuit.

Does the voltage measure near the specified value?

400 mV

Go to Step 6

Go to Step 7

6
  1. Turn OFF the ignition.
  2. Disconnect the PCM.
  3. Test the HO2S 2 low signal circuit for continuity.
  4. If the HO2S 2 low signal circuit measures over 5 ohms, repair as necessary. Refer to Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 13

Go to Step 9

7

  1. Turn OFF the ignition.
  2. Disconnect the PCM.
  3. Test the HO2S 2 high signal circuit and the HO2S 2 low signal circuit for continuity between the PCM harness connector and the HO2S 2 harness connector.
  4. If the HO2S 2 high signal circuit or the HO2S 2 low signal circuit measures over 5 ohms, repair as necessary. Refer to Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 13

Go to Step 10

8
  1. Inspect the HO2S 2 high signal circuit or the low signal circuit for a poor connection at the HO2S 2 harness connector.
  2. If a problem is found, repair as necessary. Refer to Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 13

Go to Step 11

9
  1. Inspect the HO2S 2 low signal circuit for a poor connection at the PCM.
  2. If a problem is found, repair as necessary. Refer to Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 13

Go to Step 12

10
  1. Inspect the HO2S 2 high signal circuit for a poor connection at the PCM.
  2. If a problem is found, repair as necessary. Refer to Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 13

Go to Step 12

11

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

Did you complete the replacement?

--

Go to Step 13

--

12

Replace the PCM. Refer to Powertrain Control Module Replacement .

Did you complete the replacement?

--

Go to Step 13

--

13
  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 14

Go to Step 2

14

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