GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Buick 🢒 2001 🢒 LeSabre 🢒 DTC 🢒 DTC P0140

Circuit Description

The powertrain control module (PCM) supplies a bias voltage of about 450 mV between the heated oxygen sensor (HO2S) high signal and low signal circuits. When measured with a DMM, this may display as low as 320 mV. The oxygen sensor varies the voltage within a range of about 1000 mV when the exhaust is rich, down through about 10 mV when exhaust is lean. The PCM constantly monitors the HO2S signal during closed loop operation, and 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 be set, indicating an open HO2S high signal or HO2S low signal circuit.

Conditions for Running the DTC
    • DTCs P0101, P0102, P0103, P0107, P0108, P0112, P0113, P0117, P0118, P0121, P0122, P0123, P0125, P0128, P0201, P0202, P0203, P0204, P0205, P0206, P0410, P0440, P0442, P0443, P0446, P0449, or P1441 are not set.
    • The engine run time is longer than 240 seconds.

Conditions for Setting the DTC

The HO2S 2 signal voltage remains between 425-475 mV for up to 90 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.

Test Description

The number below refers to the number on the diagnostic table:

  1. If the DTC P0140 test passes while the Failure Records conditions are being duplicated, an intermittent condition is indicated. Reviewing the Failure Records vehicle mileage since the diagnostic test last failed may help to determine how often the condition that caused the DTC to be set occurs. This may help to diagnose the condition.

DTC P0140 - HO2S Circuit Insufficient Activity Sensor 2

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
  1. Verify that the engine is at normal operating temperature.
  2. Operate the engine above 1200 RPM for 2 minutes while monitoring HO2S 2 voltage on the scan tool.

Does the scan tool indicate HO2S 2 voltage varying outside the specified values?

425-475 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, and note parameters.
  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 on the PCM side to ground.
  3. With a scan tool observe the 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. Leave the HO2S low signal circuit jumpered to ground.
  2. Use a DMM in order to measure the voltage between the HO2S 2 high signal circuit on the PCM side and the HO2S 2 heater ground circuit.

Does the voltage measure near the specified valve?

4.5 V

Go to Step 6

Go to Step 7

6
  1. Turn OFF the ignition.
  2. Disconnect the PCM.
  3. Check continuity of the HO2S 2 low signal circuit. Refer to Testing for Continuity and Testing for Intermittent Conditions and Poor Connections in Wiring Systems:
  4. If the HO2S 2 low signal circuit measures more than 5 ohms, repair the open or the poor connection as necessary.

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. Check the continuity of the HO2S 2 high signal circuit between the PCM harness connector and the HO2S 2 harness connector. Refer to following procedures in Wiring Systems:
  4. If the HO2S 2 high signal circuit measures more than 5 ohms, repair the open or the poor connection as necessary. Refer to following procedures 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 or low signal circuit for a poor connection at the HO2S 2 harness connector. Refer to following procedures in Wiring Systems:
  2. If a condition is found, replace the terminals as necessary. Refer to following procedures in Wiring Systems:
    3. •  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 terminal connection at the PCM. Refer to the following procedures in Wiring Systems:
  2. If a condition is found, replace the terminal as necessary. Refer to the following procedures 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 or replace the HO2S low signal circuit terminal connection at the PCM. Refer to the following procedures in Wiring Systems:
  2. If a condition is found, replace the terminals as necessary. Refer to the following procedures 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. 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 in Capture Info.

Does the scan tool display any DTCs that you have not diagnosed?

--

Go to Diagnostic Trouble Code (DTC) List

System OK