Circuit Description
In order to control emissions of hydrocarbons (HC), carbon monoxide (CO), and oxides of nitrogen (NOx), a 3-way catalytic converter is used. The catalyst within the converter promotes a chemical reaction which oxidizes the HC and the CO present in the exhaust gas, converting them into harmless water vapor and carbon dioxide. The catalyst also reduces NOx, converting the NOx to nitrogen. The powertrain control module (PCM) has the ability to monitor this process using the post-catalyst heated oxygen sensor (HO2S). This HO2S produces an output signal which indicates the oxygen storage capacity of the catalyst, this in turn indicates the catalysts ability to convert exhaust gases efficiently. If the post HO2S signal voltage remains excessively low for an extended period of time, this DTC will set.
Conditions for Running the DTC
| • | DTCs P0101, P0102, P0103, P0107, P0108, P0112, P0113, P0117, P0118, P0121, P0122, P0123, P0125, P0128, P0201, P0202, P0203, P0204, P0205, P0206, P0410, P0440, P0442, P0443, P0446, P0449, or P1441 are not set. |
| • | The Closed Loop commanded air/fuel ratio is between 14.5-14.8. |
| • | The accelerator pedal position (APP) indicated angle is between 5-40 percent. |
| • | The engine coolant temperature (ECT) is more than 75°C (165°F). |
Conditions for Setting the DTC
The post-HO2S signal voltage remains less than 60 mV during normal Closed Loop operation.
OR
The post-HO2S signal voltage remains less than 600 mV during power enrichment mode.
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
Inspect for the following conditions:
| • | Low fuel pressure--A condition which causes a lean exhaust can cause this DTC to set. The system will go lean if pressure is too low. The PCM can compensate for some decrease. However, if fuel pressure is too low, this DTC may set. Refer to Fuel System Diagnosis . |
| • | Fuel injector leaks--Refer to Fuel System Diagnosis . |
| • | Vacuum leaks--Inspect for a disconnected or damaged vacuum hoses and for vacuum leaks at the intake manifold, throttle body, EGR system, and crankcase ventilation system. |
| • | Exhaust leaks--An exhaust leak may cause outside air to be pulled into the exhaust gas stream past the HO2S, causing this DTC to set. Inspect for exhaust leaks near the O2S. |
| • | MAF sensor faulty--Disconnect the MAF sensor and see if the condition is corrected. If so, replace MAF sensor. Refer to Mass Airflow Sensor Replacement . |
| • | Fuel contamination--Water, even in small amounts, can be delivered to the fuel injectors. The water 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 the condition is intermittent, refer to Intermittent Conditions .
Test Description
The numbers below refer to the step numbers on the diagnostic table.
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This DTC setting during power enrichment mode conditions may indicate a condition described in the Diagnostic Aids above. If this DTC test passes while the Failure Records conditions are being duplicated, an intermittent condition is indicated. Review the Failure 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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The new PCM must be programmed.
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 |
Important: During this step, observe the pre-catalyst HO2S voltage parameters. If the pre-catalyst parameters remain below 400 mV, refer to Diagnostic Aids.
Does the HO2S voltage remain less than the specified value? | 60 mV | Go to Step 4 | Go to Step 3 |
Operate vehicle within Failure Records conditions. Does the scan tool indicate this DTC failed this ignition? | -- | Go to Step 4 | Go to Diagnostic Aids | |
4 | Disconnect HO2S and jumper the HO2S low signal circuit, on the PCM side, to a good ground. Does scan tool indicate HO2S voltage near the specified value? | 450 mV | Go to Diagnostic Aids | Go to Step 5 |
5 | Test the HO2S high signal circuit for a short to ground or a short to the sensor ground circuit. Refer to Circuit Testing in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 6 | Go to Step 7 |
6 | Repair the HO2S high signal circuit. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 8 | -- |
Replace the PCM. Refer to Powertrain Control Module Replacement . Did you complete the replacement? | -- | Go to Step 8 | -- | |
8 |
Does the DTC run and pass? | -- | Go to Step 9 | Go to Step 2 |
9 | With a scan tool, observe the stored information, Capture Info. Does the scan tool display any DTCs that you have not diagnosed? | -- | System OK | |
