DTC P0140. Chevrolet Impala 2002

For 1990-2009 cars only

Makes 🢒 Chevrolet 🢒 2002 🢒 Impala 🢒 Engine 🢒 Engine Controls - 3.8L 🢒 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 powertrain control module (PCM) operates in an Open Loop mode, ignoring the HO2S signal voltage when calculating the air-to-fuel ratio. The PCM 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 in Closed Loop. 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 provide an accurate voltage signal. The HO2S 2 is used for post catalyst monitoring. This DTC will set if the HO2S 2 voltage remains at or near the bias voltage amount.

Each HO2S 2 has the following circuits:

•	HO2S 2 high signal

•	HO2S 2 low signal

•	HO2S 2 heater ignition 1 voltage

•	HO2S 2 heater ground

Conditions for Running the DTC

•	DTCs P0101, P0102, P0103, P0106, P0107, P0108, P0112, P0113, P0116, P0117, P0118, P0121, P0122, P0123, P0125, P0128, P0201, P0202, P0203, P0204, P0205, P0206, P0410, P0440, P0442, P0443, P0446, P0449, and P1441 are not set.

•	The engine run time is longer than 240 seconds.

Conditions for Setting the DTC

The DTC will set if the HO2S 2 voltage signal remains between 400-500 mV for longer than 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 operating conditions to the Freeze Frame and updates the Failure Records.

Conditions for Clearing the MIL/DTC

•	The PCM turns OFF the MIL after 3 consecutive ignition cycles that the diagnostic runs and passes.

•	A current, DTC last test fails, clears when the diagnostic runs and passes.

•	A DTC stored in history clears after 40 warm-up cycles, if no failures are reported by this or any other emission related diagnostic.

•	A scan tool can be used to clear the DTC.

Test Description

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

The HO2S 2 voltage may default to the Bias voltage. The DTC should be cleared and the Freeze Frame/Failure Records data recorded before proceeding. A normally functioning HO2S 2 voltage signal will fluctuate above and below the bias voltage amount. The action in the test step should result in a visible reaction from the HO2S 2 output.

A voltage reading other than the specified amount in this step indicates an open circuit condition in one of the signal circuits or the PCM.

This step inspects for an open circuit condition in the signal circuits, independent of the PCM.

The conditions listed in the table may contribute to the failure of the HO2S. The conditions listed apply only to this type of failure.

Step

Action

Values

Yes

Schematic Reference: Engine Controls Schematics

Did you perform the Diagnostic System Check-Engine Controls?

Go to Step 2

Go to Diagnostic System Check - Engine Controls

If DTC P0138 and P0140 are both set, diagnose DTC P0140 first.
Allow the engine to idle at operating temperature.
Clear the DTC and record the Freeze Frame/Failure Records data if the HO2S 2 voltage is fixed at bias voltage.
Vary the engine speed from idle to 3,000 RPM several times within 5 seconds.
Observe the HO2S 2 voltage parameter using a scan tool.

Does the HO2S 2 voltage fluctuate above and below the specified value?

375-475 mV

Go to Step 3

Go to Step 4

Observe the Freeze Frame/Failure Records data for this DTC.
Turn OFF the ignition for 30 seconds.
Start the engine.
Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text or as close to the Freeze Frame/Failure Records data that you observed.

Does the DTC fail this ignition?

Go to Step 4

Go to Intermittent Conditions

Disconnect the HO2S 2 connector.
Turn ON the ignition, with the engine OFF.
Connect a 3-amp fused jumper wire between the HO2S 2 low signal circuit and a good ground.
Connect a 3-amp fused jumper wire between the HO2S 2 high signal circuit and a good ground.
Observe the HO2S 2 voltage parameter with a scan tool.

Does the HO2S 2 voltage measure less than the specified amount?

25 mV

Go to Step 7

Go to Step 5

With the ignition OFF disconnect the PCM. Refer to Powertrain Control Module Replacement .
Leave the HO2S 2 disconnected.
Measure the resistance of the HO2S 2 high signal circuit.
Measure the resistance of the HO2S 2 low signal circuit. Refer to Circuit Testing in Wiring Systems.

Is the resistance within the specified range?

0-5 ohms

Go to Step 9

Go to Step 6

Repair the signal circuit that has an open or high resistance condition. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

Go to Step 12

Before continuing inspect for the following conditions that may affect the HO2S operation:

Notice: Contamination of the oxygen sensor can result from the use of an inappropriate RTV sealant (not oxygen sensor safe) or excessive engine coolant or oil consumption. Remove the HO2S and visually inspect the portion of the sensor exposed to the exhaust stream in order to check for contamination. If contaminated, the portion of the sensor exposed to the exhaust stream will have a white powdery coating. Silicon contamination causes a high but false HO2S signal voltage (rich exhaust indication). The control module will then reduce the amount of fuel delivered to the engine, causing a severe driveability problem. Eliminate the source of contamination before replacing the oxygen sensor.

•	HO2S contamination

Notice: Do not remove the pigtail from either the heated oxygen sensor (HO2S) or the oxygen sensor (O2S). Removing the pigtail or the connector will affect sensor operation.

Handle the oxygen sensor carefully. Do not drop the HO2S. Keep the in-line electrical connector and the louvered end free of grease, dirt, or other contaminants. Do not use cleaning solvents of any type.

Do not repair the wiring, connector or terminals. Replace the oxygen sensor if the pigtail wiring, connector, or terminal is damaged.

This external clean air reference is obtained by way of the oxygen sensor signal and heater wires. Any attempt to repair the wires, connectors, or terminals could result in the obstruction of the air reference and degraded sensor performance.

The following guidelines should be used when servicing the heated oxygen sensor:

•	Do not apply contact cleaner or other materials to the sensor or vehicle harness connectors. These materials may get into the sensor causing poor performance.

•	Do not damage the sensor pigtail and harness wires in such a way that the wires inside are exposed. This could provide a path for foreign materials to enter the sensor and cause performance problems.

•	Ensure the sensor or vehicle lead wires are not bent sharply or kinked. Sharp bends or kinks could block the reference air path through the lead wire.

•	Do not remove or defeat the oxygen sensor ground wire, where applicable. Vehicles that utilize the ground wired sensor may rely on this ground as the only ground contact to the sensor. Removal of the ground wire will cause poor engine performance.

•

Ensure that the peripheral seal remains intact on the vehicle harness connector in order to prevent damage due to water intrusion. The engine harness may be repaired using Packard's Crimp and Splice Seals Terminal Repair Kit. Under no circumstances should repairs be soldered since this could result in the air reference being obstructed.

•	Chafed, burnt, cut, pinched, or otherwise damaged HO2S wiring

•	The HO2S must have a clean air reference in order to function properly. This clean air reference is obtained by way of the HO2S wires. Obstruction of the air reference and degraded HO2S performance could result from any attempt to repair the above conditions.

•	Exhaust system leaks or restrictions

•	Evaporative Emissions (EVAP) canister purge

Inspect the EVAP control system. Refer to Inspection/Maintenance Evaporative Emission System Set .

•	The fuel pressure

Incorrect fuel pressure can affect HO2S operation. Refer to Fuel System Diagnosis .

Did you find and correct the condition?

Go to Step 12

Go to Step 8

Before continuing, inspect for poor connections at the HO2S 2 connector. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.

Did you find and correct the condition?

Go to Step 12

Go to Step 10

Inspect for poor connections at the PCM harness connectors. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.

Did you find and correct the condition?

Go to Step 12

Go to Step 11

Replace the HO2S 2. Refer to Heated Oxygen Sensor 2 Replacement .

Did you complete the replacement?

Go to Step 12

Replace the PCM. Refer to Powertrain Control Module Replacement .

Did you complete the replacement?

Go to Step 12

Use the scan tool in order to clear the DTCs.
Turn OFF the ignition for 30 seconds.
Start the engine.
Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text.

Does the DTC run and pass?

Go to Step 13

Go to Step 2

With a scan tool, observe the stored information, Capture Info.

Does the scan tool display any DTCs that you have not diagnosed?

Go to Diagnostic Trouble Code (DTC) List

System OK