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 if the HO2S or the HO2S circuit has developed an open.

CONDITIONS FOR SETTING THE DTC

The following conditions will set this 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 intrusive test in progress

^ No device controls active

^ System voltage is at least 9.0 volts

^ The engine run time is greater than 2 minutes

^ HO2S voltage reading more than 394 mV but less than 473 mV

HO2 Sensor Temperature Test

^ Not in DFCO (Decel Fuel Cutoff Mode)

^ ECT is greater than 80°C

^ MAF is greater than 15 g/s

HO2S Sensor Open Test Enable

^ The DTC P0141 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 the MIL OFF after 3 consecutive drive trips when the test has Pun and Passed and not Failed.

^ A history DTC will clear if no fault conditions have been detected for 40 warm-up cycles (coolant temperature has risen 22°C (40°F) from the startup coolant temperature and the engine coolant temperature exceeds 70°C (160°F) during the same ignition cycle).

^ Use the scan tool Clear Information function.

^ Disconnect the VCM battery feed for 30 seconds.

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.