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 test has been run and failed. |
| • | The PCM will store conditions which were present when the DTC set as Freeze Frame/Failure Records data. |
Conditions for Clearing the MIL/DTC
| • | The PCM will turn OFF the malfunction indicator lamp (MIL) during the third consecutive trip in which the diagnostic has 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. Refer to Heated Oxygen Sensor Replacement . |
Many situations may lead to an intermittent condition. Perform each inspection or test as directed.
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.
| • | Loose terminal connection |
| - | Use a corresponding mating terminal to test for proper tension. Refer to Testing for Intermittent Conditions and Poor Connections , and to Connector Repairs in Wiring Systems for diagnosis and repair. |
| - | Inspect the harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, and faulty terminal to wire connection. Refer to Testing for Intermittent Conditions and Poor Connections , and to Connector Repairs in Wiring Systems for diagnosis and repair. |
| • | 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. Refer to Wiring Repairs in Wiring Systems for diagnosis and repair. |
| • | Inspect the powertrain control module (PCM) and the engine grounds for clean and secure connections. Refer to Wiring Repairs in Wiring Systems for diagnosis and repair. |
If the condition is determined to be intermittent, reviewing the Snapshot or Freeze Frame/Failure Records may be useful in determining when the DTC or condition was identified.
Test Description
The numbers below refer to the step numbers on the diagnostic table.
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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.
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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.
Step | Action | Values | Yes | No |
|---|---|---|---|---|
1 | Did you perform the Powertrain On-Board Diagnostic (OBD) System Check? | -- | ||
2 |
Does the scan tool indicate HO2S 2 voltage varying outside the specified values? | 412-499 mV | ||
Does the scan tool indicate that the DTC failed this ignition? | -- | Go to Diagnostic Aids | ||
4 |
Does the HO2S 2 voltage measure less than the specified value? | 150 mV | ||
5 |
Does the HO2S 2 signal voltage measure more than the specified value? | 950 mV | ||
6 |
Did you find and correct the condition? | -- | ||
7 |
Did you find and correct the condition? | -- | ||
8 | Inspect for a faulty HO2S 2 signal or a low circuit terminal connection at the HO2S 2 harness connector. Refer to Testing for Intermittent Conditions and Poor Connections , and Connector Repairs in Wiring Systems. Did you find and correct the condition? | -- | ||
9 | Inspect for a faulty HO2S 2 low circuit terminal connection at the PCM. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems. Did you find and correct the condition? | -- | ||
10 | Inspect for a faulty HO2S 2 signal circuit terminal connection at the PCM. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems. Did you find and correct the condition? | -- | ||
11 | Replace the HO2S 2. Refer to Heated Oxygen Sensor Replacement . Did you complete the replacement? | -- | -- | |
|
Important: : The replacement PCM must be programmed. Replace the PCM. Refer to Powertrain Control Module Replacement/Programming . Did you complete the replacement? | -- | -- | ||
13 |
Does DTC reset? | -- | System OK |
