GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Saturn 🢒 2003 🢒 L300/LW300 🢒 DTC 🢒 DTC P0140 or P0160

Object Number: 1247847 Size: MF
Engine Controls Component Views
Engine Controls Schematics

Circuit Description

The heated oxygen sensor (HO2S) produces a voltage that varies between 100-900 mV under normal operating conditions. The engine control module (ECM) produces a bias voltage on the HO2S signal circuit of 420-480 mV. The reference ground for the sensor is provided through the ECM. The ECM monitors the signal voltage to determine if the exhaust is lean or rich. The oxygen sensor voltage is high when the exhaust is rich, and low when the exhaust is lean. The ECM constantly monitors the HO2S signal during the Closed Loop operation. If the ECM detects that the HO2S voltage parameter is not moving outside of a specified range, DTC P0140 will set for bank 1 sensor 2 or DTC P0160 will set for bank 2 sensor 2.

Conditions for Running the DTC
    • The ECT parameter is more than 4°C (40°F).
    • The Battery Voltage parameter is more than 10.5 volts.
    • The calculated catalytic converter temperature is less than 800°C (1,472°F).
    • The above conditions have been met for more than 90 seconds.

Conditions for Setting the DTC

The ECM detects that the HO2S voltage parameter has not moved outside the range of 421-479 mV for more than 1 minute.

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.

Step

Action

Values

Yes

No

Schematic Reference: Engine Controls Schematics

Connector End View Reference: Engine Controls Connector End Views or Engine Control Module Connector End Views

1

Did you perform the Diagnostic System Check-Engine Controls?

--

Go to Step 2

Go to Diagnostic System Check - Engine Controls

2
  1. Operate the engine at normal operating temperature for 2 minutes.
  2. Observe the affected HO2S resistance parameter on the scan tool.

Is the resistance greater than the specified value?

175 ohms

Go to Step 10

Go to Step 3

3
  1. Observe the Freeze Frame/Failure Records for this DTC.
  2. Turn OFF the ignition for 90 seconds.
  3. Start the engine.
  4. Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records.

Did the DTC fail this ignition?

--

Go to Step 4

Go to Intermittent Conditions

4
  1. Turn OFF the ignition.
  2. Disconnect the affected heated oxygen sensor (HO2S) sensor.
  3. Turn ON the ignition, with the engine OFF.
  4. Observe the affected HO2S voltage parameter with a scan tool.

Is the HO2S voltage parameter above the specified value?

500 mV

Go to Step 5

Go to Step 7

5

Measure the voltage from the HO2S low signal circuit, on the engine harness side, to a good ground with a DMM. Refer to Circuit Testing in Wiring Systems.

Is the voltage more than the specified value?

35 mV

Go to Step 12

Go to Step 6

6

Measure the voltage from the HO2S high signal circuit, on the engine harness side, to a good ground with a DMM. Refer to Circuit Testing in Wiring Systems.

Is the voltage more than the specified value?

550 mV

Go to Step 13

Go to Step 16

7
  1. Connect a 3-amp fused jumper wire between the HO2S high signal circuit, on the engine harness side, and a good ground.
  2. Observe the HO2S voltage parameter with a scan tool.

Is the voltage less than the specified value?

35 mV

Go to Step 8

Go to Step 14

8
  1. Remove the jumper wire from the previous step.
  2. Connect a 3-amp fused jumper wire between the HO2S high signal circuit and the HO2S low signal circuit, on the engine harness side.
  3. Observe the HO2S voltage parameter with a scan tool.

Is the voltage less than the specified value?

35 mV

Go to Step 9

Go to Step 15

9

Measure the voltage from the HO2S heater low control circuit, on the engine harness side, to a good ground with a DMM Refer to Circuit Testing in Wiring Systems.

Is the voltage less than the specified value?

3.4 V

Go to Step 11

Go to Step 19

10

Measure the resistance of the following circuits with a DMM:

    • The HO2S heater low control circuit
    • The HO2S heater ignition 1 voltage circuit

Refer to Circuit Testing in Wiring Systems.

Is the resistance of either circuit more than the specified value?

5 ohms

Go to Step 17

Go to Step 19

11

Test the HO2S heater low control circuit for a short to the HO2S low signal circuit. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 20

Go to Step 16

12

Test the HO2S low signal circuit for a short to voltage. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 20

Go to Step 16

13

Test the HO2S high signal circuit for a short to voltage or a short to the heater low control circuit. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 20

Go to Step 16

14

Test the HO2S high signal circuit for an open or high resistance. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 20

Go to Step 16

15

Test the HO2S low signal circuit for an open or high resistance. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 20

Go to Step 16

16

Test for shorted terminals and poor connections at the Engine Control Module (ECM). 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 20

Go to Step 18

17

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

Did you complete the repair?

--

Go to Step 20

--

18

Replace the ECM. Refer to Engine Control Module Replacement .

Did you complete the replacement?

--

Go to Step 20

--

19

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 20

--

20
  1. Clear the DTCs with a scan tool.
  2. Turn OFF the ignition for 90 seconds.
  3. Start the engine.
  4. Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records.

Did the DTC fail this ignition?

--

Go to Step 2

Go to Step 21

21

Observe the Capture Info with a scan tool.

Are there any DTCs that have not been diagnosed?

--

Go to Diagnostic Trouble Code (DTC) List

System OK