Circuit Description
The powertrain control module (PCM) supplies a bias voltage of about 450 mV between the HO2S signal circuit and the HO2S low circuit. When measured with a 10 megohm digital voltmeter, this voltage may display as low as 350 mV. The oxygen sensor signal varies from about 800 mV when the exhaust is rich, to about 50 mV when the 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 the injector pulse width as necessary. If the HO2S 1 voltage remains excessively low for an extended period of time, DTC P0131 will set.
Conditions for Running the DTC
| • | DTCs P0101, P0102, P0103, P0106, P0107, P0108, P0111, P0112, P0113, P0117, P0118, P0121, P0122, P0123, P0200, P0410, P0412, P0418, P0440, P0442, P0443, P0446, P0449, P1106, P1107, P1111, P1112, P1114, P1115, P1121, P1122, or P1441 are not set. |
| • | The system voltage is more than 9 volts. |
| • | The Closed Loop commanded air/fuel ratio is between 14.4-14.9. |
| • | The throttle angle is between 3-40 percent. |
Conditions for Setting the DTC
The HO2S 1 signal voltage remains below 175 mV during normal Closed Loop operation.
OR
The HO2S 1 signal voltage remains below 600 mV during Power Enrichment Mode fuel control operation.
Either of the above conditions is present for up to 50 seconds.
Action Taken When the DTC Sets
| • | The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails. |
| • | The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records. |
Conditions for Clearing the MIL/DTC
| • | The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail. |
| • | A current DTC, Last Test Failed, clears when the diagnostic runs and passes. |
| • | A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic. |
| • | Clear the MIL and the DTC with a scan tool. |
Diagnostic Aids
Notice: Use the connector test adapter kit J 35616-A for any test that
requires probing the following items:
• The PCM harness connectors • The electrical center fuse/relay cavities • The component terminals • The component harness connector
Check for the following conditions:
| • | Incorrectly routed heated oxygen sensor wiring--The sensor pigtail may be routed incorrectly and contacting the exhaust system. |
| • | Faulty PCM to engine block grounds--Refer to Ground Distribution Schematics in Wiring Systems. |
| • | Fuel pressure that is too low--The system will go lean if the fuel pressure is too low. The PCM can compensate for some decrease. However, if fuel pressure is too low, a DTC P0131 may be set. Refer to DTC P0131 . |
| • | Problems with the fuel injectors--Refer to Fuel Injector Solenoid Coil Test . |
| • | Vacuum leaks--Check for the following conditions: |
| - | Disconnected or damaged vacuum hoses--Refer to Emission Hose Routing Diagram . |
| - | An incorrectly installed or malfunctioning crankcase ventilation valve |
| - | Leaks at the throttle body, the EGR valve, and the intake manifold mounting surfaces |
| • | Exhaust leaks--An exhaust leak may cause outside air to be pulled into the exhaust gas stream past the HO2S, making the system appear lean. Check for exhaust leaks that may be producing a false lean condition. |
| • | Fuel contamination--Even small amounts of water in the fuel injectors can cause a lean exhaust to be indicated. Excessive alcohol in the fuel can also cause this condition. Refer to Alcohol/Contaminants-in-Fuel Diagnosis . |
| • | If none of the above conditions are present, replace the affected HO2S. Refer to Heated Oxygen Sensor 1 Replacement . |
If the problem is intermittent, refer to Intermittent Conditions .
Test Description
The numbers below refer to the step numbers on the diagnostic table.
Step | Action | Values | Yes | No | ||||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Schematic Reference: Engine Controls Schematics | ||||||||||||||||||||||||
1 | Did you perform the Diagnostic System Check-Engine Controls? | -- | Go to Step 2 | |||||||||||||||||||||
2 |
Is the HO2S voltage less than the value specified? | 86 mV | Go to Step 4 | Go to Step 3 | ||||||||||||||||||||
Was a condition found and repaired? | -- | Go to Step 10 | Go to Diagnostic Aids. | |||||||||||||||||||||
4 |
Is the HO2S voltage within the value range specified? | 351-551 mV | Go to Step 5 | Go to Step 6 | ||||||||||||||||||||
5 |
Was a condition found and repaired? | -- | Go to Step 10 | Go to Step 8 | ||||||||||||||||||||
6 |
Is infinite resistance measured on both tests? | -- | Go to Step 9 | Go to Step 7 | ||||||||||||||||||||
7 | Repair the HO2S high signal circuit shorted to ground or shorted to the HO2S low reference circuit. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | Go to Step 10 | -- | ||||||||||||||||||||
8 | Replace the HO2S. Refer to Heated Oxygen Sensor 1 Replacement . Did you complete the replacement? | -- | Go to Step 10 | -- | ||||||||||||||||||||
9 | Replace the PCM. Refer to Powertrain Control Module Replacement . Did you complete the replacement? | -- | Go to Step 10 | -- | ||||||||||||||||||||
10 |
Does the DTC run and pass? | -- | Go to Step 11 | Go to Step 2 | ||||||||||||||||||||
11 | With a scan tool, observe the stored information, Capture Info. Does the scan tool display any DTCs that you have not diagnosed? | -- | System OK | |||||||||||||||||||||
