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For 1990-2009 cars only
Makes 🢒 Oldsmobile 🢒 1999 🢒 Intrigue 🢒 DTC 🢒 DTC P0140 HO2S Circuit Insufficient Activity Sensor 2

Object Number: 293722 Size: MF
(HO2S) #1, (HO2S) #2
Engine Controls Components
OBD II Symbol Description Notice
ESD Notice

Circuit Description

The PCM supplies a bias voltage of about 450 mV between the HO2S signal and low circuits. When measured with a 10 megohm digital voltmeter, this may display as low as 350 mV. The oxygen sensor varies the voltage within a range of about 800 mV when the exhaust is rich, down through about 50 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 injector pulse width as necessary. If the HO2S 2 voltage remains at or near the 450 mV bias for an extended period of time, DTC P0140 will be set, indicating an open sensor signal or sensor low circuit.

Conditions for Running the DTC
    • No active fuel trim, fuel injector circuit, Misfire, EVAP, EGR, TP, IAT, MAP, ECT, CKP, or MAF sensor DTCs present.
    • Engine running for at least 3.3 minutes.

Conditions for Setting the DTC

HO2S 2 signal voltage remains between 425 mV and 475 mV for up to 90 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 the MIL Off after three consecutive drive trips that the diagnostic runs and does not fail.
    • A last test failed (current DTC) clears when the diagnostic runs and does not fail.
    • A History DTC clears after forty consecutive warm-up cycles, if this or any other emission related diagnostic does not report any failures.
    • Use a scan tool in order to clear the MIL/DTC.
    • Interrupting the PCM battery voltage may or may not clear DTCs. This practice is not recommended. Refer to Powertrain Control Module (PCM) Description , Clearing Diagnostic Trouble Codes.

Diagnostic Aids

Notice: Use the connector test adapter kit J 35616-A for any test that requires probing the following items:

   • The PCM harness connectors
   • The electrical center fuse/relay cavities
   • The component terminals
   • The component harness connector
Using this kit will prevent damage caused by the improper probing of connector terminals.

Check for a malfunctioning HO2S heater or heater circuit. With the ignition ON, engine not running the HO2S voltage displayed on a scan tool should gradually drop to below 250 mV or rise to above 600 mV. If not, disconnect the HO2S and connect a test light between the HO2S ignition feed and heater ground circuits. If the test light does not light, repair the open ignition feed or sensor ground circuit as necessary. If the test light lights and the HO2S signal and low circuits are OK, replace the affected HO2S. Refer to Heated Oxygen Sensor Replacement .

If the problem is intermittent, refer to Intermittent Conditions .

The heated oxygen sensors (HO2S) require an air reference for proper operation. The air reference is supplied through the HO2S wiring. Inspect the HO2S wires and connections for breaks or contamination. Do not use solder to repair HO2S wiring. Solder will obstruct the air path. Refer to Heated Oxygen Sensor Wiring Repairs in Wiring Systems for proper repair procedures.

Test Description

The number(s) below refer to the step number(s) on the diagnostic table.

  1. This step checks for proper 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 the PCM and the High and Low circuits between the PCM and the HO2S connector for proper operation.

    3.

  3. This step checks for proper HO2S heater circuit operation up to the HO2S connector.

    4.

  4. This step checks for proper circuit resistance between the HO2S Low circuit and PCM ground.

    5.

  5. This step checks for proper circuit resistance between the HO2S Low circuit and PCM ground with a COLD sensor. A loose HO2S or poor thread to exhaust electrical contact will cause higher resistance when the HO2S is cold. Although 500 ohms is allowed, typical resistance should be less than 50 ohms.

Step

Action

Value(s)

Yes

No

1

Did you perform the Powertrain On-Board Diagnostic (OBD) System Check?

--

Go to Step 2

Go to Powertrain On Board Diagnostic (OBD) System Check

2
  1. Clear DTCs using a scan tool.
  2. Reset the Fuel Trim values.
  3. Start and idle the engine until normal operating temperature is reached.
  4. Using a scan tool monitor the HO2S voltage for the sensor that applies to this DTC.

Is the HO2S voltage fixed within the voltage range specified?

351 to 551 mV

Go to Step 4

Go to Step 3

3

The condition that set this DTC is not present. This DTC may have been set by one of the following conditions:

    • HO2S connector water intrusion
    • An intermittently open HO2S High signal circuit
    • An intermittently open HO2S Low circuit
    • An HO2S Low circuit with high resistance to ground
    • PCM ground circuits with high resistance to ground
    • An in-operative HO2S heater
    • Poor HO2S or PCM connector terminal contact
    • An exhaust system leak (typically within 12 inches up-stream of the HO2S)
    • A defective HO2S

Repair any of the above conditions as necessary.

Was a condition found and repaired?

--

Go to Step 17

Refer to Dignostic Aids.

4
  1. Turn the ignition Off.
  2. Disconnect the HO2S connector for the sensor that applies to this DTC.
  3. Jumper the HO2S Low circuit to a known good ground.
  4. Jumper the HO2S High signal circuit to a known good ground.
  5. Turn the ignition On leaving the engine Off.
  6. Using a scan tool monitor the HO2S voltage for the sensor that applies to this DTC.

Is the HO2S voltage less than the value specified?

20 mV

Go to Step 7

Go to Step 5

5
  1. Turn the ignition Off.
  2. Remove the jumpers from the HO2S terminals.
  3. Disconnect the PCM connector containing the HO2S High and Low circuits.
  4. Using the DMM J 39200 measure the continuity of the HO2S High signal circuit and then the HO2S Low circuit between the PCM connector terminal and the HO2S connector terminal (engine harness side).

Is the individual resistance of both circuits less than the value specified?

5 ohms

Go to Step 6

Go to Step 9

6
  1. Check for proper PCM connector terminal contact.
  2. Repair PCM terminals as necessary.

Was a PCM terminal repair made?

--

Go to Step 17

Go to Step 16

7
  1. Remove the jumpers from the HO2S terminals.
  2. Connect a test lamp between the HO2S Heater ignition feed and heater ground circuit terminals (engine harness side).

    3. Ensure the ignition is On while the engine is Off.

Is the test lamp illuminated?

--

Go to Step 8

Go to Step 10

8
  1. Turn the ignition Off.
  2. Reconnect the HO2S connector.
  3. Disconnect the PCM connector containing the HO2S Low circuit and the PCM connector containing the PCM ground circuits.
  4. Using the DMM J 39200 measure the resistance between the HO2S Low circuit terminal and one of the PCM ground circuit terminals.

Is the resistance measured less than the value specified?

500 ohms

Go to Step 12

Go to Step 11

9

Repair the circuit that measured high resistance.

Is the action complete?

--

Go to Step 17

--

10

Repair the HO2S Heater ignition or ground circuit. Probable causes include the following:

    • an open circuit
    • high circuit resistance
    • poor ground connection
    • a blown heater fuse (other DTCs should set)

Is the action complete?

--

Go to Step 17

--

11

Repair the high resistance between the HO2S Low circuit and the PCM ground circuit. Probable causes include the following:

    • poor HO2S connector terminal contact
    • an open sensor harness Low circuit (requires HO2S replacement)
    • a sensor harness Low circuit with high resistance (requires HO2S replacement)
    • poor PCM ground connection
    • high PCM ground circuit resistance
    • an ungrounded exhaust system

Is the action complete?

--

Go to Step 17

--

12
  1. Check for exhaust system leaks upstream of the suspect HO2S.

    2. The leak may be very small and will typically be within 12 inches of the suspect HO2S.

  2. Repair exhaust as necessary.

Was an exhaust system repair made?

--

Go to Step 17

Go to Step 13

13
  1. Allow engine to cool to ambient temperature.
  2. Using the DMM J 39200 , re-measure the resistance between the HO2S Low circuit terminal and a PCM ground circuit terminal.

Is the resistance less than the value specified?

500 ohms

Go to Step 15

Go to Step 14

14
  1. Remove the HO2S from the exhaust.
  2. Clean the HO2S mounting threads.
  3. Apply anti-seize compound 5613695 or equivalent to the sensor threads.
  4. Tighten the HO2S to the proper torque. Refer to Heated Oxygen Sensor Replacement .
  5. Using the DMM J 39200 , re-measure the resistance between the HO2S Low circuit terminal and a PCM ground circuit terminal.

Is the resistance less than the value specified?

500 ohms

Go to Step 17

Go to Step 15

15

Replace the HO2S sensor Heated Oxygen Sensor Replacement .

Is the action complete?

--

Go to Step 17

--

16

Replace the PCM. Refer to Powertrain Control Module Replacement/Programming .

Is the action complete?

--

Go to Step 17

--

17
  1. Clear DTCs with the scan tool.
  2. Turn the key to Off and wait 15 seconds.
  3. Operate the vehicle within the conditions that are required for this diagnostic to run. Refer to Conditions for Running the DTC.

Does the scan tool indicate that this test ran and passed?

--

Go to Step 18

Go to Step 2

18

Review Captured Info using the scan tool.

Are there any DTCs that have not been diagnosed?

--

Go to the applicable DTC table

System OK