Circuit Description
To control emissions of Hydrocarbons (HC), Carbon Monoxide (CO), and Oxides of Nitrogen (NOx), a three-way catalytic converter is used. The catalyst within the converter promotes a chemical reaction which oxidizes the HC and CO present in the exhaust gas, converting them into harmless water vapor and carbon dioxide. The catalyst also reduces NOx, converting it to nitrogen. The PCM has the ability to monitor this process using the Bank 1 HO2S 2 and the Bank 1 HO2S 3 heated oxygen sensors. The Bank 1 HO2S 2 sensor produces an output signal which indicates the amount of oxygen present in the exhaust gas entering the three-way catalytic converter. The Bank 1 HO2S 3 sensor produces an output signal which indicates the oxygen storage capacity of the catalyst; this in turn indicates the catalyst's ability to convert exhaust gases efficiently. If the catalyst is operating efficiently, the Bank 1 HO2S 2 signal will be far more active than that produced by the Bank 1 HO2S 3 sensor. If the Bank 1 HO2S 2 signal voltage remains at or near the 450 mV bias for an extended period of time, DTC P0140 will be set.
Conditions for Setting the DTC
| • | No active transmission, TP sensor, EVAP system, EGR, misfire, IAT sensor, MAP sensor, fuel trim, fuel injector circuit, EVAP solenoid ODM, ECT sensor, or MAF sensor DTC(s) present. |
| • | Engine run time longer than 200 seconds. |
| • | Bank 1 HO2S 2 signal voltage remains between 424 mV and 475 mV for longer than 90 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 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 the scan tool. |
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 the HO2S voltage displayed on a scan tool should gradually drop to below 250 mV. 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. |
| • | 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 Table;
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If the DTC P0140 test passes while the Fail Records conditions are being duplicated, an intermittent condition is indicated. Review the Fail Records vehicle mileage since the diagnostic test last failed. This may help determine how often the condition that caused the DTC to be set occurs.
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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 |
|---|---|---|---|---|
Schematic Reference: Engine Controls Schematics | ||||
1 | Was the Powertrain On-Board Diagnostic (OBD) System Check performed? | -- | ||
2 |
Does scan tool indicate Bank 1 HO2S 2 voltage varying outside the specified values? | 425-475 mV | ||
Does the scan tool indicate DTC P0140 failed this ignition? | -- | Go to Diagnostic Aids | ||
4 |
Is Bank 1 HO2S 2 voltage below the specified value? | 150 mV | ||
5 |
Does Bank 1 HO2S 2 voltage measure near the specified value? | 450 mV | ||
6 |
Was Bank 1 HO2S 2 low circuit problem found and corrected? | -- | ||
7 |
Was a Bank 1 HO2S 2 signal circuit problem found and corrected? | -- | ||
8 | Check for a poor Bank 1 HO2S 2 signal or low circuit terminal connection at the Bank 1 HO2S 2 harness connector and replace terminal(s) if necessary. Refer toHeated Oxygen Sensor (O2S) Repair in Electrical Diagnosis. Did any terminals require replacement? | -- | ||
9 | Check for poor Bank 1 HO2S 2 low circuit terminal connection at the PCM and replace terminal if necessary. Refer to Heated Oxygen Sensor (HO2S) Repair in Electrical Diagnosis. Did the terminal require replacement? | -- | ||
10 | Check for poor Bank 1 HO2S 2 signal circuit terminal connection at the PCM and replace terminal if necessary. Refer to Heated Oxygen Sensor (HO2S) Repair in Electrical Diagnosis. Did the terminal require replacement? | -- | ||
11 | Replace Bank 1 HO2S 2. Refer to Heated Oxygen Sensor Replacement . Is the action complete? | -- | -- | |
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 the action complete? | -- | -- | ||
14 | Locate and repair cause of high resistance (corroded exhaust flange bolts, separated exhaust flange). Is the action complete? | -- | -- | |
15 |
Does the scan tool indicate DTC P0140 failed this ignition? | -- | System OK | |
