Circuit Description
The PCM provides a 0.45 volt reference to the oxygen sensor on CKT 1665. When the Oxygen Sensor reaches operating temperature it will generate a counter voltage that will vary based on the amount of oxygen in the exhaust. The pre-converter heated oxygen sensor is located in the manifold before the catalytic converter. A lean exhaust will generate a low voltage and cause the 0.45 reference to move lower. A rich exhaust will generate a high voltage and cause the 0.45 reference to move higher. If the oxygen sensor cannot respond under the test conditions and generate a voltage greater than 0.609 volt or less than 0.307 volt, it will set a DTC P0140.
Possible causes of DTC P0140.
| • | Open in CKT 1665 or 1653. |
| • | Short to voltage on CKT 1665 or 1653. |
| • | Oxygen sensor that malfunctions. |
| • | An ineffective oxygen sensor heater. |
| • | A poor HO2S ground. |
Conditions for Setting the DTC
Test Conditions
| • | DTCs P0117, P0118, P0121, P0122, P0123, and P0560 not set. |
| • | Coolant temperature 72.5°C (163°F) or greater. |
| • | Throttle between 1.0 and 81.6 degrees. |
| • | Throttle position switch open. |
| • | Engine speed 800 RPM or greater. |
Failure Condition
Oxygen sensor voltage stays between 0.307 volt and 0.609 volt for 42 out of 64 seconds (oxygen sensor voltage not toggling).
Action Taken When the DTC Sets
| • | The PCM will illuminate the malfunction indicator lamp (MIL) when the diagnostic runs and fails. |
| • | The PCM will record operating conditions at the time the diagnostic fails. This information will be stored in the Freeze Frame and Failure Records. |
Conditions for Clearing the MIL/DTC
| • | The PCM will turn the MIL OFF after three consecutive drive trips that the diagnostic runs and does not fail. |
| • | A Last Test Failed (current) DTC will clear when the diagnostic runs and does not fail. |
| • | A History DTC will clear after forty consecutive warm-up cycles with no failures of any emission related diagnostic test. |
| • | Use a scan tool to clear DTCs. |
| • | Interrupting PCM battery voltage may or may not clear DTCs. This practice is not recommended. Refer to Clearing Diagnostic Trouble Codes in PCM Description and Operation. |
Diagnostic Aids
Notice: Do not solder heated oxygen sensor wires. Soldering the wires will result in the loss of the air reference to the sensor. Refer to Engine Electrical for proper wire and connection repair techniques.
A loose HO2S or one with a poor exhaust ground may cause this DTC to set. Before replacing an HO2S always check the resistance of the sensor ground. On a COLD engine, measure the resistance between the HO2S low circuit and the PCM ground at the PCM connector. If the resistance measures more than 500 ohms (typically less than 50 ohms), remove the sensor and check for corrosion at the HO2S sensor threads. Clean the HO2S sensor threads, apply a coating of anti-seize compound (5613695 or equivalent) and torque the HO2S sensor to the proper torque. Recheck HO2S ground resistance and replace any sensor with resistance above 500 ohms.
Test Description
Number(s) below refer to the step number(s) on the Diagnostic Table.
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Voltage on scan tool should fluctuate above 0.6 volt and below 0.3 volt. If voltage remains above 0.6 volt, check the Pre HO2S High circuit for a short to voltage. If voltage remains below 0.3 volt, check the Pre HO2S High circuit for a short to ground.
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Measuring voltage with a voltmeter will isolate a sensor/wiring problem from a PCM problem.
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When starting with a cool sensor, amperage should start at 1.5 amps and slowly drop to about 0.9 amps. This verifys that the heater is actually producing heat.
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
1 | Was the Powertrain On-Board Diagnostic (OBD) System Check performed? | -- | Go to A Powertrain On Board Diagnostic (OBD) System Check | |
Does voltage remain between the specified values? | 85°C (185°F) 0.3 - 0.6 volts | |||
Does voltage remain between the specified values? | 0.3 - 0.6 volts | Go to DTC P0139 HO2S Slow Response Bank 1 Sensor 2 | ||
4 |
Is the resistance the same or less than the value specified? | 5 ohms | ||
5 | Measure the resistance between PCM connector C2 terminal 68 and oxygen sensor connector terminal A. Is the resistance the same or less than the value specified? | 5 ohms | ||
6 |
Is the voltage more than the value specified? | 10.5 volts | ||
Is the amperage between the values specified? | 0.9 - 1.5 amps | |||
8 | Measure the voltage from oxygen sensor terminal D (harness side) to ground. Is the voltage the same or higher than the value specified? | 10.5 volts | ||
9 | Repair the open in the Pre HO2S High circuit. Is the repair complete? | -- | Go to Powertrain Control Module Diagnosis for Verify Repair | -- |
10 | Repair the open in the Pre HO2S Low circuit. Is the repair complete? | -- | Go to Powertrain Control Module Diagnosis for Verify Repair | -- |
11 | Repair the open in the Pre HO2S ground circuit. Is the repair complete? | -- | Go to Powertrain Control Module Diagnosis for Verify Repair | -- |
12 | Repair the open or short to ground (blown fuse) in the Pre HO2S Ignition feed circuit. Is the repair complete? | -- | Go to Powertrain Control Module Diagnosis for Verify Repair | -- |
13 | Replace the oxygen sensor. Refer to Heated Oxygen Sensor (HO2S) Replacement (Pre- and Post-Converter) . Is the replacement complete? | -- | Go to Powertrain Control Module Diagnosis for Verify Repair | -- |
14 |
Was terminal contact repaired? | -- | Go to Powertrain Control Module Diagnosis for Verify Repair | |
15 | Replace the PCM. Refer to PCM Replacement/Programming . Is the replacement complete? | -- | Go to Powertrain Control Module Diagnosis for Verify Repair | -- |
