P0140

Diagnostic Chart (Part 1 Of 3):

Diagnostic Chart (Part 2 Of 3):

Diagnostic Chart (Part 3 Of 3):

Schematic:

CIRCUIT DESCRIPTION
In order to control emissions, a catalytic converter converts any harmful exhaust emissions into harmless water vapor and carbon dioxide.

The Powertrain Control Module (PCM) has the capability to monitor this process by using a rear heated oxygen sensor (HO2S 2). The HO2S 2, located in the exhaust stream past the catalytic converter, produces an output signal which indicates the storage capacity of the catalyst. This in turn indicates the catalyst's ability to convert the exhaust emissions effectively. If the catalyst is functioning properly, the HO2S 2 signal will be far less active than the signal produced by the front oxygen sensor (O2S 1).

Replace the entire HO2S 2 assembly. Do not attempt to repair the HO2S 2 if the following conditions exist:
^ Damaged wiring
^ Damaged electrical connectors
^ Damaged terminals

Obstruction of the air reference and degraded HO2S 2 performance could result from any attempt to repair the above conditions.

The HO2S 2 must have a clean air reference in order for the HO2S 2 to function properly. This clean air reference is obtained by way of the HO2S 2 wires.

CONDITIONS FOR RUNNING THE DTC
^ DTCs P0105, P0107, P0108, P0112, P0113, P0117, P0118, P0122, P0123, P0171, P0201, P0202, P0203, P0204, P0300, P0335, P0440, P0442, P0446, P0506, P0507, P0601, P0602, or P1441 are not set.
^ The air flow is more than 5.5 grams per second.
^ The Engine Coolant Temperature (ECT) is more than 40°C (104°F).
^ The Throttle Position (TP) is between percent and 56 percent.

CONDITIONS FOR SETTING THE DTC
HO2S 2 remains between 425 mV and 460 mV for 125 seconds.

ACTION TAKEN WHEN THE DTC SETS
^ The Malfunction Indicator Lamp (MIL) will illuminate after two consecutive ignition cycles in which the diagnostic runs with the malfunction present.
^ The PCM will record the operating conditions at the time that the diagnostic fails. This information will store in the Freeze Frame and Failure Records buffers.
^ A history DTC stores.
^ The coolant fan turns ON.

CONDITIONS FOR CLEARING THE MIL/DTC
^ The MIL will turn OFF after three consecutive ignition cycles in which the diagnostic runs without a fault.
^ A history DTC will clear after 40 consecutive warm-up cycles without a fault.
^ Use a scan tool to clear the DTCs.

DIAGNOSTIC AIDS
An intermittent could be the result of the following conditions:
^ A faulty electrical connection
^ Moisture in the electrical connector or connector wiring
^ Rubbed-through wire insulation
^ A broken wire inside the insulation Check for the following conditions:
^ A faulty electrical connection or a damaged harness - Inspect the PCM harness for an open in the HO2S 2 signal circuit. Check for the following conditions:
- Improper mating
- Broken locks
- Improperly-formed connectors
- Damaged terminals
- A faulty terminal-to-wire connection
- A damaged harness
^ Intermittent test - Observe the HO2S 2 on the scan tool while moving the related electrical connectors and the wiring harness with the ignition switch ON. If the malfunction is induced, the HO2S 2 display will change. This test should help isolate the location of the malfunction.

Replace the entire HO2S 2 assembly. Do not attempt to repair the HO2S 2 if the following conditions exist:
^ Damaged wiring
^ Damaged electrical connector
^ Damaged terminals

Obstruction of the air reference and degraded HO2S 2 performance could result in any attempt to repair the above conditions.

The HO2S 2 must have a clean air reference in order for the HO2S 2 to function properly. This clean air reference is obtained by way of the HO2S 2 wires.

TEST DESCRIPTION
The numbers below refer to the step numbers on the diagnostic table.
2. This step checks for proper 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 proper operation.
7. This step checks for proper HO2S heater circuit operation up to the HO2S connector.
8. This step checks for proper circuit resistance between the HO2S LOW circuit and PCM ground.
13. This step checks for proper circuit resistance between the HO2S LOW circuit and PCM ground with a COLD sensor. A loose HO2S or poor thread to the 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.