P0140

DTC P0140

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 engine control module (ECM) operates in an open loop mode, ignoring the HO2S signal voltage when calculating the air-to-fuel ratio. The ECM supplies the HO2S with a reference, or bias, voltage of about 450 mV. The HO2S generates a voltage within a range of 0-1,000 mV that fluctuates above and below bias voltage once the sensor reaches operating temperature. High HO2S voltage output indicates a rich fuel mixture; low HO2S voltage output indicates a lean mixture. Heating elements inside the HO2S minimize the time required for the sensors to reach operating temperature, and to provide an accurate voltage signal. The ECM monitors the rich-to-lean and lean-to-rich transition time. If the ECM detects an HO2S 2 voltage signal that remains at or near the bias voltage, DTCs P0140 or P0160 will set.

Each HO2S has the following circuits:
- The HO2S high signal circuit
- The HO2S low signal circuit
- The HO2S heater ignition 1 voltage circuit
- The HO2S heater low control circuit

CONDITIONS FOR RUNNING THE DTC
- The engine is running.
- The Calc Converter Temp parameter is less than 800°C (1,472°F).
- The Battery Voltage parameter is more than 10.5 volts.

CONDITIONS FOR SETTING THE DTC
- The ECM detects no affected HO2S 2 sensor activity, and the affected HO2S 2 voltage is between 400-520 mV for more than 600 seconds.

OR

- The ECM detects that the affected HO2S 2 internal resistance is more than 40,000 ohms.

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

Steps 1-3:

Steps 4-6:

Steps 7-9:

Steps 10-11:

Steps 12-17:

The numbers below refer to the step numbers on the diagnostic table.
9. This test verifies whether or not the affected HO2S is internally shorted to voltage prior to replacing the ECM.
14. Both components must be replaced since the shorted HO2S has damaged the ECM low reference circuit.