Circuit Description
The PCM supplies a bias voltage of about 450 mV between the HO2S signal and low circuits. When measured with a digital voltmeter, this may display as low as 320 mV. The oxygen sensor varies the voltage within a range of about 1000 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 DTC will be set.
Conditions for Running the DTC
| • | No Misfire, CKP, Fuel injector, MAF, TP, EVAP, IAT, MAP, Fuel trim, EGR or ECT DTCs are present. |
| • | 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 |
| • | Throttle angle is between 5 percent and 40 percent |
Conditions for Setting the DTC
HO2S signal voltage remains more than 975 mV during normal closed loop operation
OR
HO2S signal voltage remains more than 200 mV during decel fuel cutoff.
Action Taken When the DTC Sets
| • | The PCM will illuminate the malfunction indicator lamp (MIL) during the second consecutive trip in which the diagnostic test has been run and failed. |
| • | The PCM will store conditions which were present when the DTC set as Freeze Frame/Failure Records data. |
Conditions for Clearing the MIL/DTC
| • | The PCM will turn OFF the malfunction indicator lamp (MIL) during the third consecutive trip in which the diagnostic has run and passed. |
| • | The history DTC will clear after 40 consecutive warm-up cycles have occurred without a malfunction. |
| • | The DTC can be cleared by using a scan tool. |
Diagnostic Aids
Inspect for the following:
| • | 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 Pressure Test . |
| • | Fuel injectors contaminated or faulty -- Refer to Fuel Injector Balance Test . |
| • | Inspect the EVAP Canister for Fuel Saturation. If the EVAP Canister is full of fuel, inspect canister control and hoses. Refer to Evaporative Emission Control System Diagnosis . |
| • | Disconnect the MAF sensor and see if the rich condition is corrected. If so, replace the MAF sensor. |
| • | 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 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 1000 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. |
| • | Open HO2S Signal or Low Circuit or Faulty HO2S -- A poor connection or open in the HO2S signal or low 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 300mV to 600mV, inspect the HO2S signal and low circuit wiring and associated terminal connections. If the wiring and connections are OK, replace the HO2S. |
If the DTC is determined to be intermittent, reviewing the Fail Records can be useful in determining when the DTC was last set.
Test Description
The numbers below refer to step numbers on the diagnostic table:
-
This DTC failing during deceleration fuel mode operation (vehicle speed above 25 mph, TP angle below 3 percent) may indicate a condition described in Diagnostic Aids. If this DTC test passes while the Fail Records conditions are being duplicated, an intermittent condition is indicated. Review the Fail 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.
-
This vehicle is equipped with a PCM which utilizes an Electrically Erasable Programmable Read Only Memory (EEPROM). When the PCM is replaced, the new PCM must be programmed.
Step | Action | Values | Yes | No |
|---|---|---|---|---|
1 | Did you perform the Powertrain On-Board Diagnostic (OBD) System Check? | -- | ||
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? | 600 mV | ||
Operate vehicle in Decel fuel mode (vehicle speed above 25 mph, 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 | |||
4 | Operate the vehicle within the Fail Records conditions. Does the scan tool indicate this DTC failed this ignition? | -- | Go to Diagnostic Aids | |
5 | Disconnect the HO2S. Does scan tool indicate HO2S voltage more than the specified value? | 500 mV | ||
6 | Test for a short to voltage on the HO2S signal circuit. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | -- | ||
|
Important: The replacement PCM must be programmed. Replace the PCM. Refer to Powertrain Control Module Replacement/Programming . Did you complete the repair? | -- | -- | ||
8 | Replace the HO2S. Refer to Heated Oxygen Sensor Replacement . Did you complete the repair? | -- | -- | |
9 |
Does the DTC reset? | -- | System OK |
