P0140

Circuit Description

The PCM provides a 0.45 volt reference to the oxygen sensor on CKT 1665. When the Oxygen Sensor reaches operating temperature it will generate a counter voltage that will vary based on the amount of oxygen in the exhaust. The preconverter heated oxygen sensor is located in the manifold before the catalytic converter. A lean exhaust will generate a low voltage and cause the 0.45 reference to move lower. A rich exhaust will generate a high voltage and cause the 0.45 reference to move higher. If the oxygen sensor cannot respond under the test conditions and generate a voltage greater than 0.609 volt or less than 0.307 volt, it will set a DTC P0140.

Possible causes of DTC P0140.

^ Open in CKT 1665 or 1653.

^ Short to voltage on CKT 1665 or 1653.

^ Oxygen sensor that malfunctions.

^ An ineffective oxygen sensor heater.

Conditions for Setting the DTC

Test Conditions
^ DTCs P0117, P0118, P0121, P0122, P0123, and P0560 not set.

^ Coolant temperature 72.5°C (163°F) or greater.

^ Throttle between 1.0 and 81.6 degrees.

^ Throttle position switch open.

^ Engine speed 800 RPM or greater.

Failure Condition
Oxygen sensor voltage stays between 0.307 volt and 0.609 volt for 42 out of 64 seconds (oxygen sensor voltage not toggling).


Action Taken When the DTC Sets

^ The PCM will illuminate the Malfunction Indicator Lamp (MIL) when the diagnostic runs and fails.

^ The PCM will record operating conditions at the time the diagnostic fails. This information will be stored in the Freeze Frame and Failure Records.


Conditions for Clearing the MIL/DTC

^ The PCM will turn the MIL OFF after three consecutive drive trips that the diagnostic runs and does not fail.

^ A Last Test Failed (current) DTC will clear when the diagnostic runs and does not fail.

^ A History DTC will clear after forty consecutive warm-up cycles with no failures of any emission related diagnostic test.

^ PCM battery voltage is interrupted. Using a Scan tool.

Diagnostic Aids

Notice: Never solder heated oxygen sensor wires. For proper wire and connection repair, refer to Section 8.


Test Description

Number(s) below refer to the step number(s) on the Diagnostic Table.

2. Voltage on scan tool should fluctuate above 0.6 volt and below 0.3 volt. If voltage remains above 0.6 volt, check the Pre HO2S High circuit for a short to voltage. If voltage remains below 0.3 volt, check the Pre HO2S High circuit for a short to ground.

3. Measuring voltage with a voltmeter will isolate a sensor/wiring problem from a PCM problem.

7. When starting with a cool sensor, amperage should start at 1.5 amps and slowly drop to about 0.9 amps. This verifies that the heater is actually producing heat.