Circuit Description
The PCM supplies a bias voltage of about 450 mV between the HO2S signal and low circuits. When measured with a 10 megohm digital voltmeter, this may display as low as 320 mV. The oxygen sensor varies the voltage within a range of about 1000 mV when the exhaust is rich, down through about 10 mV when exhaust is lean. The PCM constantly monitors the HO2S signal during closed loop operation and compensates for a rich or lean condition by decreasing or increasing injector pulse width as necessary. If the HO2S 2 voltage remains at or near the 450 mV bias for an extended period of time, DTC P0140 will be set, indicating an open sensor signal or sensor low circuit.
Conditions for Running the DTC
| • | No active Transaxle, TP sensor, EVAP system, EGR Pintle, ECT sensor, IAT sensor, CKP sensor, Misfire, Fuel Trim, Fuel Injector Circuit, MAF sensor, or MAP system DTC(s) present. |
| • | Engine run time longer than 3 minutes. |
Conditions for Setting the DTC
HO2S 2 signal voltage remains between 425mV and 475mV for longer than 90 seconds.
Action Taken When the DTC Sets
| • | The PCM will illuminate the 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 and Fail Records data. |
Conditions for Clearing the MIL/DTC
| • | The PCM will turn the MIL OFF 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 the scan tool Clear Info function or by disconnecting the PCM battery feed. |
Diagnostic Aids
Check for the following conditions:
| • | Corroded exhaust flange bolts. Using a DVM, ensure that continuity exists between the engine block and the heated oxygen sensor shell. If resistance is excessively high, replace corroded exhaust flange attaching hardware as necessary. |
| • | Poor connection or damaged harness. Inspect the harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal to wire connection, and damaged harness. |
| • | Faulty HO2S heater or heater circuit. With the ignition ON, engine OFF, the HO2S voltage displayed on a scan tool should gradually drop to below 250mV. If not, disconnect the HO2S and connect a test light between the HO2S ignition feed and heater ground circuits. If the test light does not light, repair the open ignition feed or sensor ground circuit as necessary. If the test light lights and the HO2S signal and low circuits are OK, replace the HO2S. Refer to Heated Oxygen Sensor Replacement . |
| • | Intermittent test. With the ignition ON, monitor the HO2S signal voltage while moving the wiring harness and related connectors. If the fault is induced, the HO2S signal voltage will change. This may help isolate the location of the malfunction. |
Test Description
Number(s) below refer to the step number(s) on the Diagnostic Chart.
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If the DTC P0140 test passes while the Fail Records conditions are being duplicated, an intermittent condition is indicated. Reviewing the Fail Records vehicle mileage since the diagnostic test last failed may help 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 utilizes an Electrically Erasable Programmable Read Only Memory (EEPROM). When the PCM is being replaced, the new PCM must be programmed.
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
1 | Was the Powertrain On-Board Diagnostic (OBD) System Check performed? | -- | ||
2 |
Does scan tool indicate HO2S 2 voltage varying outside the specified values? | 425-475mV | ||
Does scan tool indicate DTC P0140 failed this ign? | -- | Refer to Diagnostic Aids | ||
4 |
Is HO2S 2 voltage below the specified value? | 150mV | ||
5 |
Does HO2S 2 voltage measure near the specified value? | 450mV | ||
6 |
Was a problem found? | -- | ||
7 |
Was a problem found? | -- | ||
8 | Check for a poor HO2S 2 signal or low circuit terminal connection at the HO2S 2 harness connector and replace terminal(s) if necessary. Refer to Repair Procedures Electrical Diagnosis. Did any terminals require replacement? | -- | ||
9 | Check for poor HO2S 2 low circuit terminal connection at the PCM and replace terminal if necessary. Refer to Repair Procedures Electrical Diagnosis. Did the terminal require replacement? | -- | ||
10 | Check for poor HO2S 2 signal circuit terminal connection at the PCM and replace terminal if necessary. Refer to Repair Procedures Electrical Diagnosis. Did the terminal require replacement? | -- | ||
11 | Replace HO2S 2. Refer to Heated Oxygen Sensor Replacement . Is action completed? | -- | -- | |
12 | Measure resistance between the engine block ground and the heated oxygen sensor shell. Is the resistance greater than the specified value? | 100 ohms | ||
Replace the PCM. Important: Replacement PCM must be programmed. Refer to Powertrain Control Module Replacement/Programming . Is action complete? | -- | -- | ||
14 | Locate and repair cause of high resistance (corroded exhaust flange bolts, seperated exhaust flange, ect.) Is action complete? | -- | -- | |
15 |
Does scan tool indicate DTC P0140 failed this ign? | -- | System OK |
