P0140

Diagnostic Chart (Part 1 Of 2):

Diagnostic Chart (Part 2 Of 2):

Schematic:

CIRCUIT DESCRIPTION
A three-way catalytic converter is used in order to control emissions of Hydrocarbons (HC), Carbon Monoxide (CO), and Oxides Of Nitrogen (NOx). The catalyst within the converter promotes a chemical reaction which oxidizes the HC and the CO present in the exhaust gas, converting them into harmless water vapor and carbon dioxide. The catalyst also reduces the NOx, converting it to nitrogen. The Powertrain Control Module (PCM) has the ability to monitor this process using heated oxygen sensor HO2S 1 and HO2S 2. HO2S 1 produces an output signal which indicates the amount of oxygen present in the exhaust gas that is entering the three-way catalytic converter. HO2S 2 produces an output signal which indicates the oxygen storage capacity of the catalyst. This in turn indicates the catalyst's ability to convert the exhaust gases efficiently. If the catalyst is operating efficiently, the HO2S 1 signal will be far more active than the signal produced by HO2S 2. If the HO2S 2 signal voltage remains at or near the 450 mV bias for an extended time, DTC P0140 will set.

CONDITIONS FOR RUNNING THE DTC
^ No active TP, MAP, MAF, IAT, ECT, sensor, fuel injector circuit, EVAP, AIR DTCs are present.
^ The system voltage is between 9.0-18.0 volts.
^ The engine coolant temperature is more than 65°C (149°F).
^ The engine run time is more than 200 seconds.
^ The AIR pump is commanded OFF.

CONDITIONS FOR SETTING THE DTC
HO2S 2 signal voltage remains between 412-499 mV for more than 100 seconds.

ACTION TAKEN WHEN THE DTC SETS
^ The PCM will illuminate the Malfunction Indicator Lamp (MIL) during the second consecutive trip in which the diagnostic has been run and failed.
^ If equipped with traction control, the PCM will command the Electronic Brake And Traction Control Module (EBTCM) via the serial data circuit to turn OFF traction control, and the EBTCM will illuminate the TRACTION OFF lamp.
^ The PCM will store conditions which were present when the DTC set as Freeze Frame and Failure Records data.

CONDITIONS FOR CLEARING THE MIL/DTC
^ The PCM will turn OFF the MIL during the third consecutive trip in which the diagnostic has been run and passed.
^ The History DTC will clear after 40 consecutive warm-up cycles have occurred without a malfunction.
^ The DTC can be cleared by using a scan tool.

DIAGNOSTIC AIDS
Inspect for:
^ Corroded exhaust flange bolts-Use a DMM to ensure that continuity exists between the engine block and the heated oxygen sensor shell. If resistance is excessively high, replace the corroded exhaust flange, attaching the hardware as necessary.
^ A malfunctioning HO2S heater or heater circuit- With the ignition ON and the engine not running, the HO2S voltage displayed on a scan tool should gradually drop to less than 250 mV or rise to more than 600 mV. If not, disconnect the HO2S and connect a test lamp between the HO2S ignition feed and heater ground circuits. If the test lamp does not illuminate, repair the open ignition feed or the sensor ground circuit as necessary. If the test light illuminates and the HO2S signal and low circuits are OK, replace the affected HO2S.

IMPORTANT: Remove any debris from the connector surfaces before servicing a component. Inspect the connector gaskets when diagnosing or replacing a component. Ensure that the gaskets are installed correctly. The gaskets prevent contaminate intrusion.

^ Poor terminal connection - Inspect the harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, and faulty terminal to wire connection. Use a corresponding mating terminal to test for proper tension.
^ Damaged harness - Inspect the wiring harness for damage. If the harness inspection does not reveal a problem, observe the display on the scan tool while moving connectors and wiring harnesses related to the sensor. A change in the scan tool display may indicate the location of the fault.
^ PCM and engine grounds for clean and secure connections

If the DTC is determined to be intermittent, reviewing the Failure Records can be useful in determining when the DTC was last set.

TEST DESCRIPTION
The numbers below refer to the step numbers on the diagnostic table.
3. If the DTC P0140 test passes while the Failure Records conditions are being duplicated, an intermittent condition is indicated. Reviewing the Failure Records vehicle mileage since the diagnostic test last failed may help to determine how often the condition that caused the DTC to be set occurs. This may assist in diagnosing the condition.
12. This vehicle is equipped with a PCM which uses an Electrically Erasable Programmable Read Only Memory (EEPROM). When the PCM is replaced, the new PCM must be programmed.