Circuit Description
The engine control module (ECM) supplies a voltage of about 0.45 volts between terminals A12 and A27. If measured with a 10 megohm digital voltmeter, this may read as low as 0.32 volts. The oxygen sensor (O2S) varies the voltage within a range of about 1 volt if the exhaust is rich, down through about 0.1 volts if the exhaust is lean.
The sensor is like an open circuit and produces no voltage when it is below 315°C (600°F). An open sensor circuit or cold sensor causes open loop operation.
If the O2S pigtail wiring, connector, or terminal is damaged, the entire O2S assembly must be replaced. Do not attempt to repair the wiring, connector, or terminals. In order for the sensor to function properly, it must have a clean air reference provided to it. This clean air reference is obtained by way of the O2S wires. Any attempt to repair the wires, connector, or terminals could result in the obstruction of the air reference and degrade the O2S performance.
Conditions for Setting the DTC
| • | O2S voltage is less than 0.05 volts. |
| • | Closed loop stoichiometry |
| • | Engine coolant temperature (ECT) is greater than 60°C (140°F). |
| • | System voltage is greater than 10 volts. |
| • | DTCs P0107, P0108, P0117, P0118, P0122, P0123, P0201, P0202, P0203, P0204, P0336, P0337, P0351, P0352, and P0443 are not set. |
| • | Three second delay after conditions are met |
Action Taken When the DTC Sets
| • | The malfunction indicator lamp (MIL) will illuminate. |
| • | The ECM will record operating conditions at the time the diagnostic fails. This information will be stored in the Freeze Frame and Failure Records buffers. |
| • | A history DTC is stored. |
| • | The vehicle will operate in open loop. |
Conditions for Clearing the MIL/DTC
| • | The MIL will turn OFF after 4 consecutive ignition cycles in which the diagnostic runs without a fault. |
| • | A history DTC will clear after 40 consecutive warm-up cycles without a fault. |
| • | The DTCs can be cleared by using the scan tool. |
| • | Disconnect the ECM battery feed for more than 10 seconds. |
Diagnostic Aids
| • | Fuel pressure--The system will be lean if the fuel pressure is too low. It may be necessary to monitor the fuel pressure while driving the vehicle at various road speeds and/or loads to confirm. Refer to Fuel System Diagnosis . |
| • | Manifold absolute pressure (MAP) sensor--An output that causes the ECM to sense a lower than normal manifold pressure, high vacuum, can cause the system to go lean. Disconnecting the MAP sensor will allow the ECM to substitute a fixed, default, value for the MAP sensor. If the lean condition is gone when the sensor is disconnected, substitute a known good sensor and recheck. |
| • | Fuel contamination--Water, in even small amounts near the in-tank fuel pump inlet can be delivered to the injector. The water causes a lean exhaust and can set DTC P0131. |
| • | Sensor harness--The O2S sensor pigtail may be mis-positioned and contacting the exhaust manifold. |
| • | Engine misfire--A misfiring cylinder will result in unburned oxygen in the exhaust, which could cause DTC P0131 to set. |
| • | Cracked oxygen sensor--A cracked O2S or poor ground at the sensor could cause DTC P0131. Refer to Symptoms - Engine Controls . |
| • | Plugged fuel filter--A plugged fuel filter can cause a lean condition and cause a DTC P0131 to set. |
| • | Plugged oxygen sensor--A plugged reference port on the O2S will indicate a lower-than-normal voltage output from the O2S. |
Test Description
The numbers below refer to the step numbers on the diagnostic table.
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The On-Board Diagnostic System Check prompts the technician to complete some basic checks and store the Freeze Frame and Failure Records data on the scan tool if applicable. This creates an electronic copy of the data taken when the malfunction occurred. The information is then stored on the scan tool for later reference.
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This step determines if DTC P0131 is the result of a hard failure or an intermittent condition. It may be necessary to operate the vehicle within the Freeze Frame conditions and Conditions for Setting the DTC in order to duplicate the malfunction detected by the ECM.
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This step simulates DTC P0134. If the ECM senses the change, the ECM and the wiring are OK.
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The replacement ECM must be reprogrammed. Refer to the latest Techline procedure for ECM reprogramming.
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If no malfunctions have been found at this point and no additional DTCs were set, refer to Diagnostic Aids for additional inspections and information.
Step | Action | Values | Yes | No |
|---|---|---|---|---|
Perform an On-Board Diagnostic System Check. Is the check completed? | -- | Go to Step 2 | ||
Does the oxygen sensor (O2S) voltage remain less than the value specified? | 0.1 V | Go to Step 4 | Go to Step 3 | |
3 |
Does the O2S voltage remain less than the specified value? | 0.1 V | Go to Step 4 | Go to Step 7 |
Does the scan tool display the O2S voltage within the specified range? | 407-509 mV | Go to Diagnostic Aids | Go to Step 5 | |
5 | Inspect the O2S signal circuit, terminal 2 for a short to ground and repair as needed. Did you find and correct the condition? | -- | Go to Step 7 | Go to Step 6 |
Did you complete the replacement? | -- | Go to Step 7 | -- | |
7 |
Does the scan tool indicate that this diagnostic has run and passed? | -- | Go to Step 8 | Go to Step 2 |
Are any DTCs displayed that have not been diagnosed? | -- | Go to applicable DTC table | System OK |
