Circuit Description
The heated oxygen sensor (HO2S) is a sensor designed to create a voltage relative to the oxygen content in the engine exhaust stream. The control module supplies the HO2S with high and low signal circuits. Ignition voltage and ground are supplied to the HO2S heater by independent circuits. The oxygen content of the exhaust indicates when the engine is operating lean or rich. When the HO2S detects that the engine is operating rich, the signal voltage is high, and decreases the signal voltage as the engine runs learner. This oscillation above and below the bias voltage, sometimes referred to as activity or switching, can be monitored with the HO2S signal voltage.
The HO2S contains heater that is necessary in order to quickly warm the sensor to operating temperature. The heater also maintains the operating temperature during extended idle conditions. The HO2S needs to be at a high temperature in order to produce a voltage. When the HO2S reaches operating temperature, the control module monitors the HO2S bias, or reference, voltage. The control module also monitors the HO2S signal voltage for Closed Loop fuel control. During normal Closed Loop fuel operation, the control module will add fuel, or enrich the mixture, when the HO2S detects a lean exhaust content. The control module will subtract fuel, or "lean out" the mixture, when the HO2S detects a rich exhaust condition. Certain vehicle models use an oxygen sensor behind the catalytic converter in order to monitor the catalyst efficiency.
This diagnostic trouble code (DTC) is designed to detect an HO2S voltage that remains at a high voltage for more than a specified number of seconds during the test conditions. This DTC is set during the following conditions:
| • | There is an HO2S circuit fault that results in a false rich exhaust condition. |
| • | The HO2S is correctly detecting a rich air/fuel ratio resulting from either a fuel control fault or an emission system fault. |
Conditions for Running the DTC
| • | DTCs P0101, P0102, P0103, P0106, P0107, P0108, P0112, P0113, P0117, P0118, P0125, P0128, P0200, P0300, P0351-P0358, P0401, P0404, P0405, P0410, P0418, P0443, P0446, P0449, P1120, P1220, P1221, P1258, or P1404 are not set. |
| • | The secondary air injection (AIR) and the exhaust gas recirculation (EGR) diagnostics are not active. |
| • | The ignition voltage is more than 9 volts. |
| • | The fuel system is operating in Closed Loop. |
| • | The fuel trim learn is enabled. |
| • | The throttle position (TP) indicated angle is between 3-50 percent. |
Conditions for Setting the DTC
The HO2S signal voltage remains above 977 mV for 33 seconds or more.
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 components and systems: |
| - | The HO2S electrical connections--Inspect for evidence of water intrusion. Water present in the connector causes the ignition 1 voltage supply to the heater to bleed over to the signal circuit. |
| - | The fuel pressure--The system goes rich if the pressure is too high. The PCM compensates for some increase. However, if the fuel pressure is too high, a DTC may set. Refer to Fuel System Diagnosis . |
| - | A rich injector--Perform the Injector Balance Test. Refer to Fuel Injector Balance Test with Tech 2 . |
| - | A leaking injector-- Refer to Fuel System Diagnosis . |
| - | The fuel pressure regulator-- Inspect the vacuum line going to the fuel pressure regulator for evidence of fuel. Refer to the Fuel System Diagnosis . |
| - | Evaporative emissions (EVAP) canister purge--Inspect the canister for fuel saturation. If full of fuel, check the canister control and hoses. Refer to Evaporative Emission Control System Description . |
| - | The mass air flow (MAF) sensor -- Disconnect the MAF sensor and see if the rich condition is corrected. If so, check for proper installation. If installed OK, replace the MAF sensor. If the MAF sensor is installed backwards, the system goes rich. The plastic portion of the sensor has arrows cast into it indicating proper air flow direction. The arrows must point towards the engine. |
| - | HO2S oxygen supply--An oxygen supply inside the HO2S is necessary for proper operation. The HO2S wires provide the supply of oxygen. Inspect the HO2S wires and connections for breaks or contamination. Refer to Heated Oxygen Sensor Wiring Repairs in Wiring Systems. |
| - | The throttle position (TP) sensor--An intermittent TP sensor output causes the system to go rich, due to a false indication of the engine accelerating. |
| • | Use the Freeze Frame/Failure Records data in order to locate an intermittent condition in the following ways: |
| - | If you cannot duplicate the DTC, the information included in the Freeze Frame/Failure Records data can aid in determining how many miles since the DTC set. |
| - | The Fail Counter and Pass Counter can also aid in determining how many ignition cycles the diagnostic reported a pass or a fail. |
| - | Operate the vehicle within the same Freeze Frame conditions that you observed in order to isolate when the DTC failed. Use the following conditions for your tests: |
| • | RPM |
| • | Load |
| • | Vehicle speed |
| • | Temperature |
| - | For an intermittent condition, refer to Intermittent Conditions . |
Test Description
The number below refers to the step numbers on the diagnostic table.
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In order to determine if the engine is rich during deceleration fuel cut-off (DFCO) mode operation, operate the vehicle up to highway speed conditions and release the accelerator pedal allowing the vehicle to coast in gear. Monitor the scan tool HO2S voltage and the DFCO parameter. A rich condition will cause HO2S voltage to be more than 468 mV during DFCO.
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Monitor the HO2S voltage of the opposite bank sensor. If the voltage activity of the opposite bank sensor is similar to the voltage activity of the suspect sensor check for rich conditions that would affect both cylinder banks. An opposite bank sensor with normal HO2S voltage activity indicates the suspect HO2S is defective or a rich condition exists only on the suspect HO2S cylinder bank.
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An HO2S contaminated by silicon will have a white, powdery deposit on the portion of the HO2S that is exposed to the exhaust stream. The usual cause of silica contamination is the use of un-approved silicon RTV engine gasket material or the use of silicon based sprays or fluids within the engine. If the cause of this contamination is not corrected, the replacement HO2S will also be contaminated.
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 fixed at more than the value specified? | 976 mV | Go to Step 4 | Go to Step 3 | ||||||||||||||||
Does the DTC fail this ignition? | -- | Go to Step 4 | Go to Diagnostic Aids | |||||||||||||||||
4 |
Does the HO2S voltage measure within the specified range? | 351-551 mV | Go to Step 5 | Go to Step 6 | ||||||||||||||||
Did you find and correct the condition? | -- | Go to Step 12 | Go to Step 8 | |||||||||||||||||
6 |
Does the voltage measure more than the specified value? | 20 mV | Go to Step 7 | Go to Step 10 | ||||||||||||||||
7 | Repair the short to voltage in the HO2S high signal circuit. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 12 | -- | ||||||||||||||||
Inspect for poor connections at the harness connector of the affected HO2S. Refer to Testing for Intermittent Conditions and Poor Connections and Heated Oxygen Sensor Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 12 | Go to Step 9 | |||||||||||||||||
9 |
Important: Before replacing a contaminated HO2S determine and repair the cause of the contamination. Replace the HO2S. Refer to 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 12 | -- | ||||||||||||||||
10 | Inspect for poor connections at the harness connector of the PCM. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 12 | Go to Step 11 | ||||||||||||||||
11 | Replace the PCM. Refer to Powertrain Control Module Replacement . Did you complete the replacement? | -- | Go to Step 12 | -- | ||||||||||||||||
12 |
Did the DTC run and pass? | -- | Go to Step 13 | Go to Step 2 | ||||||||||||||||
13 | With a scan tool, observe the stored information, Capture Info. Does the scan tool display any DTCs that you have not diagnosed? | -- | System OK | |||||||||||||||||
