Circuit Description
The powertrain control module (PCM) supplies a bias voltage of about 450 mV between the heated oxygen sensor (HO2S) high signal and low signal circuits. When measured with a DMM, this may display as low as 320 mV. The oxygen sensor varies the voltage within a range of about 1,000 mV when the exhaust is rich, down through about 10 mV when 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 injector pulse width as necessary. If the HO2S voltage remains excessively high for an extended period of time, this diagnostic trouble code (DTC) will be 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 vehicle is in Closed Loop. |
| • | The air/fuel ratio is more than or equal to 14.5, but less than or equal to 14.8. |
| • | The accelerator pedal position (APP) indicated angle is between 5-40 percent. |
Conditions for Setting the DTC
The HO2S signal voltage remains more than 975 mV during normal Closed Loop operation.
Or
The HO2S signal voltage remains more than 200 mV during Decel fuel cut-off.
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:
| • | High fuel pressure--The system will go rich if pressure is too high. The PCM can compensate for some increase. However, if fuel pressure is too high, a HO2S DTC may set. Refer to Fuel System Diagnosis . |
| • | Inspect for leaking fuel injectors--Refer to Fuel System Diagnosis . |
| • | Inspect the evaporative emission (EVAP) canister for Fuel Saturation. If the EVAP canister is full of fuel, inspect canister control and hoses. Refer to Evaporative Emission System Cleaning . |
| • | Disconnect the mass air flow (MAF) sensor and see if the rich condition is corrected. If so, replace the MAF sensor. Refer to Mass Airflow Sensor Replacement . |
| • | Inspect for a leaking fuel pressure regulator diaphragm by inspecting the vacuum line to the fuel pressure regulator for the presence of fuel. |
| • | An intermittent throttle position (TP) sensor output will cause the system to go rich due to a false indication of the engine accelerating. |
| • | Shorted HO2S--If the HO2S is internally shorted the HO2S voltage displayed on the scan tool will be over 1 volt. Disconnect the affected HO2S and jumper the HO2S low circuit to ground with the key ON. If the displayed HO2S voltage changes from over 1,000 mV to around 450 mV, replace the HO2S. Silicon contamination of the HO2S can also cause a high HO2S voltage to be indicated. This condition is indicated by a powdery white deposit on the portion of the HO2S exposed to the exhaust stream. If contamination is noticed , replace the affected HO2S. Refer to Heated Oxygen Sensor Replacement - Bank 1 Sensor 1 , Heated Oxygen Sensor Replacement - Bank 1 Sensor 2 , or Heated Oxygen Sensor Replacement - Bank 2 Sensor 1 . |
| • | Open HO2S high or low signal circuit or poor HO2S--A poor connection or open in the HO2S high or low signal circuit can cause the DTC to set during deceleration fuel mode. An HO2S which is faulty and not allowing a full voltage swing between the rich and lean thresholds can also cause this condition. Operate the vehicle while monitoring the HO2S voltage with a scan tool. If the HO2S voltage is limited within a range between 300-600 mV, inspect the HO2S high and low signal circuit wiring and associated terminal connections. If the wiring and connections are OK, replace the HO2S. Refer to Heated Oxygen Sensor Replacement - Bank 1 Sensor 1 , Heated Oxygen Sensor Replacement - Bank 1 Sensor 2 , or Heated Oxygen Sensor Replacement - Bank 2 Sensor 1 . |
Refer to Intermittent Conditions .
Test Description
The numbers below refer to step numbers on the diagnostic table:
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This DTC failing during deceleration fuel mode operation, with the vehicle speed above 40 km/h (25 mph), and the TP angle below 3 percent, may indicate a condition described in Diagnostic Aids. 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 all HO2S voltage parameters. If all parameters remain above the specified value, refer to Diagnostic Aids.
Does the HO2S voltage remain above the specified value? | 975 mV | Go to Step 5 | Go to Step 3 |
Operate vehicle in decel fuel mode, with the vehicle speed above 40 km/h (25 mph) and the TP angle below 3 percent, while observing the HO2S voltage parameter on the scan tool. Does the HO2S voltage remain above the specified value while in decel fuel mode? | 110 mV | Go to Step 5 | Go to Step 4 | |
4 | Operate the vehicle within the Failure Records conditions. Does the scan tool indicate this DTC failed this ignition? | -- | Go to Step 5 | Go to Diagnostic Aids |
5 | Disconnect the HO2S. Does scan tool indicate HO2S voltage more than the specified value? | 500 mV | Go to Step 6 | Go to Step 8 |
6 | Test for a short to voltage on the HO2S high signal circuit. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | -- | Go to Step 9 | Go to Step 7 |
Replace the PCM. Refer to Powertrain Control Module Replacement . Did you complete the replacement? | -- | Go to Step 9 | -- | |
8 | Replace the HO2S. Refer to Heated Oxygen Sensor Replacement - Bank 1 Sensor 2 , Heated Oxygen Sensor Replacement - Bank 1 Sensor 1 , or Heated Oxygen Sensor Replacement - Bank 2 Sensor 1 . Did you complete the replacement? | -- | Go to Step 9 | -- |
9 |
Does the DTC run and pass? | -- | Go to Step 10 | Go to Step 2 |
10 | With a scan tool, observe the stored information, Capture Info. Does the scan tool display any DTCs that you have not diagnosed? | -- | System OK | |
