P0140

Diagnostic Chart (Part 1 Of 3):

Diagnostic Chart (Part 2 Of 3):

Diagnostic Chart (Part 3 Of 3):

Engine Controls Schematics: Heated O2 Sensors:

CIRCUIT DESCRIPTION
The PCM supplies a bias voltage of about 450 mV between the HO2S signal circuit and the HO2S low circuit. When measured with a 10 megohm digital voltmeter, this voltage may display as low as 350 mV. The oxygen sensor signal varies from about 800 mV when the exhaust is rich, to about 50 mV when the exhaust is lean. The PCM constantly monitors the HO2S signal during closed loop operation The PCM then compensates for a rich or lean condition by decreasing or increasing the injector pulse width as necessary. If the HO2S 2 voltage remains at or near the 450 mV bias for an extended period of time, DTC P0140 will set.

CONDITIONS FOR RUNNING THE DTC
^ There are no active DTCs of any of the following types present:
^ Fuel trim
^ Fuel injector circuit
^ Misfire
^ Evaporative Emissions (EVAP)
^ Exhaust Gas Recirculation (EGR)
^ Throttle Position (TP) sensor
^ Intake Air Temperature (IAT) sensor
^ Manifold Absolute Pressure (MAP) sensor
^ Engine Coolant Temperature (ECT) sensor
^ Crankshaft Position (CKP) sensor
^ Mass Air Flow (MAF) sensor
^ The engine has been running for at least 3.3 minutes.

CONDITIONS FOR SETTING THE DTC
The HO2S 2 signal voltage remains between 425-475 mV for up to 90 seconds.

ACTION TAKEN WHEN THE DTC SETS
^ The PCM illuminates the Malfunction Indicator Lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
^ The PCM records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the PCM stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the PCM records the operating conditions at the time of the failure. The PCM writes the conditions to the Freeze Frame and updates the Failure Records.

CONDITIONS FOR CLEARING THE MIL/DTC
^ The PCM turns the MIL OFF after three consecutive drive trips during which the diagnostic runs and passes.
^ A last test failed, or the current DTC, clears when the diagnostic runs and passes.
^ A History DTC clears after forty consecutive warm-up cycles, if no other emission related diagnostic failures are reported.
^ Use a scan tool in order to clear the MIL diagnostic trouble code.
^ Interrupting the PCM battery voltage may or may not clear DTCs. This practice is not recommended. Refer to Powertrain Control Module (PCM) Description, Clearing Diagnostic Trouble Codes.

DIAGNOSTIC AIDS

NOTE: Refer to Connector Test Adapter kit J 35616-A Notice in Service Precautions.

Check for a malfunctioning HO2S heater or heater circuit. With the ignition ON and the engine OFF, the HO2S voltage displayed on a scan tool should gradually drop below 250 mV or rise above 600 mV. If this does not occur, disconnect the HO2S and connect a test lamp between the HO2S ignition feed circuit and the heater ground circuit. If the test lamp does not light, repair the open ignition feed circuit or the sensor ground circuit as necessary. If the test lamp lights and the HO2S signal circuit and low circuit are OK, replace the affected HO2S. Refer to Heated Oxygen Sensor (HO2S) Replacement.

If the problem is intermittent, refer to Intermittent Conditions. Intermittent Conditions

TEST DESCRIPTION
The numbers below refer to the step numbers on the diagnostic table.
2. This step checks for correct sensor activity. When in Closed Loop fuel control, the HO2S voltage should rapidly swing above and below the bias voltage
4. This step checks the PCM and the high and low circuits between the PCM and the HO2S connector for correct operation.
7. This step checks for correct HO2S heater circuit operation up to the HO2S connector.
8. This step checks for correct circuit resistance between the HO2S low circuit and the PCM ground.
13. This step checks for proper circuit resistance between the HO2S low circuit and the PCM ground with a COLD sensor. A loose HO2S or faulty 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.