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For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 1999 🢒 Sonoma Pickup - 2WD 🢒 DTC 🢒 DTC P0140 HO2S Circuit Insufficient Activity Sensor 2

Object Number: 211067 Size: MF
Engine Controls Components
Cell 20: Oxygen Sensors
OBD II Symbol Description Notice
Powertrain Control Module Connector End Views
Handling ESD Sensitive Parts Notice

Circuit Description

The HO2S 2, located in the exhaust stream past the catalytic converter, produces an output signal relative to the oxygen storage capacity of the catalytic converter. The PCM can then determine the ability of the catalytic converter to convert the exhaust emissions effectively. The HO2S 2 signal will be far less active than the signal produced by the front Oxygen Sensor 1 (O2S 1).

Conditions for Running the DTC
    • No active MAP DTC's
    • No active IAT DTC's
    • No active ECT DTC's
    • No active TP DTC's
    • No active Fuel Trim DTC's
    • No active Injector Control DTC's
    • No active Misfire DTC's
    • No active CKP DTC's
    • No active EVAP DTC's
    • No active IAC DTC's
    • No active PCM Memory DTC's
    • Air flow is more than 5.5 grams per second.
    • Engine Coolant Temperature (ECT) is more than 40°C (104°F).
    • The above conditions met for 140 seconds.
    • Throttle Position (TP) is between 5 percent and 50 percent.

Conditions For Setting The DTC

HO2S 2 remains between 425 mV and 460 mV for 125 seconds.

Action Taken When the DTC Sets
    • The control module illuminates the malfunction indicator lamp (MIL) if a failure is detected during 2 consecutive key cycles.
    • The control module sets the DTC and records the operating conditions at the time the diagnostic failed. The failure information is stored in the scan tool Freeze Frame/Failure Records.

Conditions for Clearing the MIL or DTC
    • The control module turns OFF the MIL after 3 consecutive drive trips when the test has run and passed.
    • A history DTC will clear if no fault conditions have been detected for 40 warm-up cycles. A warm-up cycle occurs when the coolant temperature has risen 22°C (40°F) from the startup coolant temperature and the engine coolant reaches a temperature that is more than 70°C (158°F) during the same ignition cycle.
    • Use a scan tool in order to clear the DTCs.

Diagnostic Aids

Whenever the oxygen sensor pigtail wiring, the connector, or the terminal are damaged, replace the entire oxygen sensor assembly. Do not attempt to repair the wiring, connector or terminals. In order for the sensor to function properly, the rear HO2S 2 must have a clean air reference. This clean air reference is obtained by way of the oxygen sensor wires. Any attempt to repair the wires, connectors or terminals could result in the obstruction of the air reference and degrade the performance of the oxygen sensor.

A poor connection, rubbed through wire insulation or a wire broken inside the insulation may cause an intermittent.

Check for the following conditions:

    • A poor connection or damaged harness - Inspect the PCM harness for the following condition:
       - Open in the rear HO2S high circuit
       - Improper mating
       - Broken locks
       - Improperly formed or damaged terminals
       - Poor terminal to wire connection
       - Damaged harness.
    • An intermittent test - Observe the rear HO2S 2 on the scan tool while moving the related connectors and wiring harness with the key ON. Whenever the fault is induced, the rear HO2S 2 display will change. This may help isolate the location of the malfunction.

An intermittent may be caused by any of the following conditions:

    • A poor connection
    • Rubbed through wire insulation
    • A broken wire inside the insulation

Thoroughly check any circuitry that is suspected of causing the intermittent complaint. Refer to Intermittents and Poor Connections Diagnosis in Wiring Systems.

If a repair is necessary, refer to Wiring Repairs or Connector Repairs in Wiring Systems.

Test Description

The numbers below refer to the step numbers 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 VCM and the HIGH and LOW circuits between the VCM 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 VCM ground.

    5.

  5. This step checks for proper circuit resistance between the HO2S LOW circuit and VCM 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. Using a scan tool, store the DTC Information from the PCM into the scan tool.
  2. Clear the DTC Information from the PCM.
  3. Reset the Fuel Trim values.
  4. Start and idle the engine until normal operating temperature is reached.
  5. 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?

400-473 mV

Go to Step 4

Go to Step 3

3

This DTC is intermittent.

Are any additional DTCs stored?

--

Go to the applicable DTC table

Go to Diagnostic Aids

4

  1. Turn OFF the ignition.
  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 ON the ignition leaving the engine OFF.
  6. Using a scan tool monitor the HO2S voltage for the sensor that applies to this DTC.

Is the voltage less than the specified value?

20 mV

Go to Step 7

Go to Step 5

5
  1. Turn OFF the ignition.
  2. Remove the jumpers from the HO2S terminals.
  3. Disconnect the PCM connector containing the HO2S HIGH and LOW circuits.
  4. Using a 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 resistance of both circuits less than the specified value?

5 ohms

Go to Step 6

Go to Step 9

6
  1. Check for proper PCM connector terminal contact.
  2. Repair as necessary. Refer to Connector Repairs in Wiring Systems.

Did you find a problem?

--

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 positive voltage and heater ground circuit terminals (engine harness side).
  3. Ensure the ignition is ON while the engine is OFF.

Is the test lamp ON?

--

Go to Step 8

Go to Step 10

8

  1. Turn OFF the ignition.
  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 a J 39200 measure the resistance between the HO2S LOW circuit terminal and one of the PCM ground circuit terminals.

Is the resistance less than the specified value?

500 ohms

Go to Step 12

Go to Step 11

9

Repair the circuit that measured high resistance. Refer to Wiring Repairs in Wiring Systems.

Is the action complete?

--

Go to Step 17

--

10

Repair the HO2S heater ignition positive voltage circuit or ground circuit. Refer to Wiring Repairs in Wiring Systems.

Probable causes include the following:

    • An open circuit
    • High circuit resistance
    • Poor ground connection
    • 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. Refer to Wiring Repairs in Wiring Systems. Probable causes include the following:

    • Poor HO2S connector terminal contact
    • Open sensor harness LOW circuit (requires HO2S replacement)
    • 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 typically be within 12 inches of the suspect HO2S.

  2. Repair exhaust as necessary. Refer to Exhaust System Inspection in Engine Exhaust.

Did you find a problem?

--

Go to Step 17

Go to Step 13

13

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

Is the resistance less than the specified value?

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 561 3695 or equivalent to the sensor threads.
  4. Tighten the HO2S to the proper torque. Refer to Heated Oxygen Sensor Replacement .
  5. Using a J 39200 re-measure the resistance between the HO2S LOW circuit terminal and a PCM ground circuit terminal.

Is the resistance less than the specified value?

500 ohms

Go to Step 17

Go to Step 15

15

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

Is the action complete?

--

Go to Step 17

--

16

Important: The replacement PCM must be programmed.

Replace the PCM.

Refer to Powertrain Control Module Replacement/Programming .

Is the action complete?

--

Go to Step 17

--

17
  1. Using the scan tool, clear the DTC's.
  2. Start the engine.
  3. Allow the engine to idle until the engine reaches normal operating temperature.
  4. Select DTC and the Specific DTC function.
  5. Enter the DTC number which was set.
  6. Operate the vehicle, with the Condition for Setting this DTC, until the scan tool indicates the diagnostic Ran.

Does the scan tool indicate the diagnostic passed?

--

Go to Step 18

Go to Step 2

18

Does the scan tool display any additional undiagnosed DTCs?

--

Go to the applicable DTC table

System OK