GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2002 🢒 GMC C Sierra - 2WD 🢒 DTC 🢒 DTC P0140 or P0160

Circuit Description

Heated oxygen sensors (HO2S) are used for fuel control and post catalyst monitoring. Each HO2S compares the oxygen content of the surrounding air with the oxygen content of the exhaust stream. When the vehicle is first started, the powertrain control module (PCM) operates in an Open Loop mode, ignoring the HO2S signal voltage when calculating the air-to-fuel ratio. The PCM circuitry that monitors the HO2S generates a reference, or bias, voltage of 450 mV when the sensor is cold, high resistance. Once the HO2S warms up, the HO2S generates a voltage within a range of 0 -1000 mV, depending on the exhaust gas oxygen content. High HO2S voltage output indicates a rich fuel mixture. Low HO2S voltage output indicates a lean mixture. Once fueling goes Closed Loop, the HO2S voltage will fluctuate above and below the bias voltage. A heating element inside the HO2S reduces the time required for the sensor to reach operating temperature, and provide an accurate voltage signal.

This DTC is designed to detect an HO2S voltage that remains at a nominal value +/- some calibrated range for a calibrated number of seconds. This nominal value is usually the bias voltage.

Conditions for Running the DTC
    • DTCs P0101, P0102, P0103, P0106, P0107, P0108, P0112, P0113, P0116, P0117, P0118, P0200, P0300, P0351-P0358, P0400, P0401, P0404, P0405, P0410, P0440, P0442, P0443, P0446, P0449, P0452, P0453, P1120, P1125, P1220, P1221, P1258, P1404, P1441, P1514, P1515, P1516, P1517, or P1518 are not set.
    • The secondary air injection (AIR) and the exhaust gas recirculation (EGR) diagnostics are not active.
    • The system voltage is more than 9 volts.
    • The engine has been running for more than 409 seconds.
    • The system is in Closed Loop.
    • The fuel level is more than 10 percent.

Conditions for Setting the DTC
    • The change in the throttle position (TP) indicated angle is more than 5 percent for 1 second for 6 samples.
    • The HO2S voltage is between 410-490 mV for more than 145 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 numbers below refer to the step numbers on the diagnostic table.

  1. After the HO2S heater is commanded ON, the HO2S heater heats up causing the HO2S signal voltage to either increase or decrease. This indicates that the HO2S heater is OK.

    2.

  2. If the test lamp illuminates, the low reference circuit between the HO2S and PCM terminal C1-63 is OK and the PCM low reference terminal is OK.

    3.

  3. If the voltage is below the specified value, the high signal circuit, the low reference circuit, and the PCM are OK.

    4.

  4. The opposite bank HO2S must be disconnected to isolate a short to ground in the HO2S heater high control circuit.

    5.

  5. Resistance within the specified range indicates the HO2S heater is OK.

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

Important: Allow the engine to cool for one-half hour before proceeding with this diagnostic. This allows the HO2S signal voltage to return to bias voltage, approximately 447 mV.

  1. Turn OFF the ignition.
  2. Install a scan tool.
  3. Turn ON the ignition, with the engine OFF.
  4. Command the HO2S heater ON with a scan tool.
  5. Immediately observe the affected HO2S voltage for 2 minutes.

Does the HO2S voltage go from bias voltage to more than or less than the specified range?

350-550 mV

Go to Step 3

Go to Step 5

3
  1. Start the engine.
  2. Allow the engine to reach operating temperature.
  3. Raise and hold the engine speed at 1,200 RPM for 2 minutes.
  4. Observe the HO2S voltage with a scan tool.

Does the HO2S voltage vary outside the specified range?

350-550 mV

Go to Step 4

Go to Step 5

4
  1. Observe the Freeze Frame/Failure Records data for this DTC.
  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, or as close to the Freeze Frame/Failure Records data that you observed.

Does the DTC fail this ignition?

--

Go to Step 5

Go to Intermittent Conditions

5

Are both DTCs P0140 and P0160 set?

--

Go to Step 6

Go to Step 7

6

  1. Turn OFF the ignition.
  2. Disconnect the bank 1 sensor 2 HO2S connector.
  3. Probe the HO2S low reference circuit with a test lamp that is connected to battery positive.

Does the test lamp illuminate?

--

Go to Step 11

Go to Step 10

7

  1. Turn OFF the ignition.
  2. Disconnect the affected HO2S connector.
  3. Jumper the HO2S high signal circuit to the low reference circuit.
  4. Turn ON the ignition, with the engine OFF.
  5. Observe the HO2S voltage with a scan tool.

Is the HO2S voltage less than the specified value?

200 mV

Go to Step 11

Go to Step 8

8
  1. Turn OFF the ignition.
  2. Disconnect the PCM connector containing the HO2S high signal circuit. Refer to Powertrain Control Module Replacement .
  3. Test the HO2S high signal circuit for an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 21

Go to Step 9

9

Test for an open between terminal A of the affected sensor harness connector and one of the following PCM terminals:

    • If DTC P0140 is set use C1-28
    • If DTC P0160 is set use C1-25

Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 21

Go to Step 17

10
  1. Disconnect the PCM connector containing the HO2S low reference circuit. Refer to Powertrain Control Module Replacement .
  2. Test the low reference circuit for an open between HO2S bank 1 sensor 2 terminal A and PCM terminal C1-63.

    3. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 21

Go to Step 17

11

  1. If applicable, remove the jumper from the previous step.
  2. Disconnect the opposite bank HO2S connector.
  3. Perform the following:
    4. • If only one DTC is set, P0140 or P0160, probe the affected HO2S heater high control circuit with a test lamp that is connected to a good ground.
    • If both DTCs P0140 and P0160 are set, probe HO2S bank 1 sensor 2 heater high control circuit with a test lamp that is connected to a good ground.
  4. Command the HO2S heater ON with a scan tool.

Does the test lamp illuminate?

--

Go to Step 12

Go to Step 13

12
  1. Connect a test lamp between the affected HO2S heater high control circuit and the HO2S heater low control circuit or heater ground.
  2. Command the HO2S heater ON with a scan tool.

Does the test lamp illuminate?

--

Go to Step 14

Go to Step 16

13
  1. Disconnect the PCM connector containing the HO2S heater high control circuit. Refer to Powertrain Control Module Replacement .
  2. Test the HO2S heater high control circuit for an open or short to ground. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
  3. Replace fuse if necessary.

Did you find and correct the condition?

--

Go to Step 21

Go to Step 17

14

Important: Perform the following test on HO2S bank 1 sensor 2 and HO2S bank 2 sensor 2. A condition in either sensor will cause this DTC to set.

Test the HO2S heater high control circuit, sensor side, for a short to the HO2S body. Refer to Circuit Testing in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 20

Go to Step 15

15

Important: Perform the following test on HO2S bank 1 sensor 2 and HO2S bank 2 sensor 2. A condition in either sensor will cause this DTC to set.

Measure the resistance between the HO2S heater high control circuit, sensor side, and the HO2S heater low control circuit, sensor side. Refer to Circuit Testing in Wiring Systems.

Does the resistance of either sensor measure above or below the specified range?

2-50  ohms

Go to Step 20

Go to Step 18

16
  1. Disconnect the PCM connector containing the HO2S heater low control circuit. Refer to Powertrain Control Module Replacement .
  2. Test the HO2S heater low control circuit for an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 21

Go to Step 17

17

Inspect for poor connections at the harness connector of the PCM. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 21

Go to Step 19

18

Inspect for poor connections at the harness connector of the affected HO2S. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 21

Go to Step 20

19

Replace the PCM. Refer to Powertrain Control Module Replacement .

Did you complete the replacement?

--

Go to Step 21

--

20

Replace the affected HO2S. Refer to Heated Oxygen Sensor Replacement - Bank 1 Sensor 2 or Heated Oxygen Sensor Replacement - Bank 2 Sensor 2 .

Did you complete the replacement?

--

Go to Step 21

--

21
  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 as specified in the supporting text.

Does the DTC run and pass?

--

Go to Step 22

Go to Step 2

22

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