P0140

Diagnostic Chart:

Wiring Diagram:

CIRCUIT DESCRIPTION

IMPORTANT: If the voltage is measured with a 10 megohm digital voltmeter, the voltage may read as low as 0.32 volt.

The VCM supplies a voltage of about 0.45 volt (450 mV) between the HO2S High and the HO2S Low circuits.

The Heated Oxygen Sensor (HO2S) varies the voltage from approximately 1.0 volt (1000 mV) during rich conditions to 0.10 volt (100 mV) during lean conditions. The sensor is like an open circuit and produces no voltage when it is below 360°C (600°F).

The HO2S heater provides for a faster sensor warm-up which allows the sensor to become active in a shorter period of time and remain active during a long extended idle. The DTC P0140 determines it the HO2S or the HO2S circuit has developed an open.

CONDITIONS FOR SETTING THE DTC

The following conditions will set the DTC:

^ No TP Sensor DTCs.

^ No EVAP DTCs.

^ No IAT sensor DTCs.

^ No MAP sensor DTCs.

^ No ECT sensor DTCs.

^ No MAF sensor DTCs.

^ No active misfire DTCs.

^ No intrusive test in progress.

^ No device controls active.

^ The system voltage measures is greater than or equal to 9.0 volts.

^ The engine run time is greater than or equal to 2 minutes.

HO2 Sensor Temperature Test

^ Engine Running.

^ Not in DFCO.

^ ECT is greater than or equal to 80°C.

^ Air Flow is greater than or equal to 15 g/s.

HO2S Sensor Open Test Enable

^ HO2 Sensor Temperature Test = True.

^ The DTC P0141 (HO2S heater) not set.

^ Closed Loop.

ACTION TAKEN WHEN THE DTC SETS

The VCM turns the MIL ON after 2 consecutive test failures.

CONDITIONS FOR CLEARING THE MIL/DTC

The VCM turns OFF the MIL after 3 consecutive driving trips without a fault condition present. A history DTC will clear if no fault conditions have been detected for 40 warm-up cycles (the coolant temperature has risen 40°F from the start-up coolant temperature and the engine coolant temperature exceeds 160°F during that same ignition cycle) or the scan tool clearing feature has been used.

DIAGNOSTIC AIDS

IMPORTANT: Never solder the HO2S wires. For proper wire and connection repairs, refer to Wiring Repairs in Electrical Diagnosis.

A intermittent may be caused by a poor connection, a rubbed through wire insulation, or a broken wire inside the insulation.

Check for the following conditions:

^ A poor connection or a damaged harness: Inspect the harness connectors for the following conditions:

- Backed out terminals

- Improperly formed or damaged terminals

- Poor terminal to wire connection

- Damaged harness

^ 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 to below 0.150 volt, indicating that the heater works properly. If not, disconnect the HO2S and connect a test lamp between the terminals C and D. If the test lamp does not light, repair the open in the HO2S ground circuit or the HO2S ignition feed circuit. If the test lamp lights, replace the HO2S.

^ The Intermittent test: Use a scan tool in order to monitor this HO2S signal voltage. Move the related connectors and the wiring harness with a warm engine running at part throttle in Closed Loop. If the failure is induced, the HO2S signal voltage reading changes from its normal fluctuating voltage (above 600 mV and below 300 mV) to a fixed value around 450 mV. This may help to isolate the location of the malfunction.

TEST DESCRIPTION

The numbers below refer to the step numbers on the diagnostic table.

2. If the conditions for setting this DTC exist, the system will not go into a Closed Loop.

3. This test checks the continuity of the HO2S signal circuit.