Circuit Description
The heated oxygen sensors (HO2S) are used for fuel control and catalyst monitoring. Each HO2S compares the oxygen content of the surrounding air with the oxygen content of the exhaust stream. When the engine is started, the control module operates in an Open Loop mode, ignoring the HO2S signal voltage while calculating the air-to-fuel ratio. The control module supplies the HO2S with a reference, or bias voltage of approximately 450 mV. While the engine runs, the HO2S heats up and begins to generate a voltage within a range of 0-1,000 mV. This voltage will fluctuate above and below the bias voltage. Once sufficient HO2S voltage fluctuation is observed by the control module, Closed Loop is entered. The control module uses the HO2S voltage to determine the air-to-fuel ratio. An HO2S voltage that increases above bias voltage toward 1,000 mV indicates a rich fuel mixture. An HO2S voltage that decreases below bias voltage toward 0 mV indicates a lean fuel mixture.
The heating elements inside each HO2S heat the sensor to bring the sensor up to operating conditions faster. This allows the system to enter Closed Loop earlier and the control module to calculate the air-to-fuel ratio sooner.
The HO2S utilizes the following circuits:
| • | A signal circuit |
| • | A low reference circuit |
| • | An ignition 1 voltage circuit |
| • | A heater control circuit |
If the ECM detects that the HO2S voltage change during a lean-to-rich transition is less than a calculated amount, the DTC sets.
DTC Descriptor
This diagnostic procedure supports the following DTCs:
| • | DTC P0134 HO2S Insufficient Activity Bank 1 Sensor 1 |
| • | DTC P0154 HO2S Insufficient Activity Bank 2 Sensor 1 |
Conditions for Running the DTC
| • | DTCs P0030, P0031, P0032, P0050, P0051, P0052, P0131, P0132, P0133, P0151, P0152, P0153, P0171, P0172, P0174, P0175, P1171, P1172, P1174, P1175, are not set. |
| • | The engine is operating. |
| • | The ignition 1 voltage is more than 10 volts. |
| • | The fuel system is in closed loop. |
| • | The vehicle speed is more than 5 Km/h (3 mph) |
| • | The modeled catalyst temperature is more than 600°C (1,112°F). |
| • | The DTCs run continuously once the above conditions are met. |
Conditions for Setting the DTC
The ECM detects that the HO2S voltage change during a lean-to-rich transition is less than 250 mV for 60-90 seconds depending on engine speed and load.
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. |
Test Description
The numbers below refer to the step numbers on the diagnostic table.
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This step determines if the condition is present. This test may take 5-10 minutes for the diagnostic to run.
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This step tests the HO2S signal and the low reference circuit for an high resistance. The HO2S voltage should go low.
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An exhaust leak 6-12 inches away from the HO2S can cause a DTC to set.
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Certain RTV silicone gasket materials release vapors that can contaminate the HO2S. Silicone in the fuel can also cause silicone contamination. If the sensors appear contaminated by silicone, and if all the silicone sealant is a non-silicone base, advise the customer to try a different fuel company. A missing fuel filler restrictor indicates that the customer may have used leaded fuel.
Step | Action | Values | Yes | No | ||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Schematic Reference: Engine Controls Schematics Connector End View Reference: Engine Control Module Connector End Views or Engine Controls Connector End Views | ||||||||||||||||||||
1 | Did you perform the Diagnostic System Check - Engine Controls? | -- | Go to Step 2 | |||||||||||||||||
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Important: If any DTCs are set, except for P0134 or P0154, refer to those DTCs before proceeding with this diagnostic table.
Did the DTC P0134 or P0154 fail this ignition? | -- | Go to Step 4 | Go to Step 3 | |||||||||||||||||
3 |
Did the DTC fail this ignition? | -- | Go to Step 4 | Go to Intermittent Conditions | ||||||||||||||||
Is the voltage less than the specified value? | 20 mV | Go to Step 8 | Go to Step 5 | |||||||||||||||||
5 |
Is the voltage less than the specified value? | 20 mV | Go to Step 7 | Go to Step 6 | ||||||||||||||||
6 | Test the HO2S signal circuit for high resistance. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 13 | Go to Step 10 | ||||||||||||||||
7 | Test the HO2S low reference circuit for high resistance. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 13 | Go to Step 10 | ||||||||||||||||
Inspect for an exhaust leak near the oxygen sensor. Did you find and correct the condition? | -- | Go to Step 13 | Go to Step 9 | |||||||||||||||||
Inspect or test for the following conditions:
Did you find and correct the condition? | -- | Go to Step 13 | Go to Step 11 | |||||||||||||||||
10 | Test for shorted terminals and for poor connections at the harness connector of the engine control module (ECM). Refer to Testing for Intermittent Conditions and Poor Connections and Repairing Connector Terminals in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 13 | Go to Step 12 | ||||||||||||||||
11 | Replace the appropriate HO2S. Did you complete the replacement? | -- | Go to Step 13 | -- | ||||||||||||||||
12 | Replace the ECM. Refer to Engine Control Module Replacement . Did you complete the replacement? | -- | Go to Step 13 | -- | ||||||||||||||||
13 |
Did the DTC fail this ignition? | -- | Go to Step 2 | Go to Step 14 | ||||||||||||||||
14 | Observe the Capture Info with a scan tool. Are there any DTCs that have not been diagnosed? | -- | System OK | |||||||||||||||||
