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 |
The engine control module (ECM) monitors the rich-to-lean and lean-to-rich transition time. A transition is defined as the HO2S voltage changes from above 600 mV to below 300 mV or from below 300 mV to above 600 mV. If the ECM detects that the transition time is too long, this DTC sets.
DTC Descriptor
This diagnostic procedure supports the following DTC:
DTC P0133 HO2S Slow Response Sensor 1
Conditions for Running the DTC
| • | DTCs P0106, P0107, P0108, P0112, P0113, P0117, P0118, P0122, P0123, P0131, P0132, P0134, P0171, P0172, P0201-P0204, P0300, P0336, P0337, P0351, P0352, P0401, P0402, P0404, P0405, P0406, P0441, P0443, P0488, P0502, P0506, P0507, P2195, and P2196 are not set. |
| • | The engine coolant temperature (ECT) is more than 70°C (158°F). |
| • | The ignition 1 voltage is more than 10 volts. |
| • | The fuel system is in closed loop. |
| • | The engine run time is more than 60 seconds. |
| • | The engine speed is between 1,600-4,300 RPM. |
| • | The calculated air flow is between 9-40 g/s. |
| • | The evaporative emission (EVAP) purge is less than 20 percent. |
| • | DTC P0133 runs once per ignition cycle once the above conditions are met for 2 seconds. |
Conditions for Setting the DTC
| • | The ECM detects that the HO2S 1 rich-to-lean average response time is less than 100 milliseconds for an automatic transmission and 85 milliseconds for a manual transmission or lean-to-rich average response time is more than 125 milliseconds for an automatic transmission and 100 milliseconds for a manual transmission. |
| OR |
| • | The ECM detects that the HO2S 1 rich-to-lean or lean-to-rich switches are less than 10. |
| OR |
| • | The ECM detects that the HO2S 1 signal spends twice the amount of time in the rich region as compared to the lean region or the HO2S 1 signal spends twice the amount of time in the lean region as compared to the rich region. |
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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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 P0133, refer to those DTCs before proceeding with this diagnostic table.
Did DTC P0133 fail this ignition cycle? | -- | Go to Step 4 | Go to Step 3 | |||||||||||||||||||||
3 |
Did the DTC fail this ignition? | -- | Go to Step 4 | Go to Intermittent Conditions | ||||||||||||||||||||
Inspect for an exhaust leak near the heated oxygen sensor (HO2S). Refer to Symptoms - Engine Exhaust in Engine Exhaust. After you inspect the exhaust system, return to this diagnostic. Did you find and correct the condition? | -- | Go to Step 7 | Go to Step 5 | |||||||||||||||||||||
Inspect or test for the following conditions:
Did you find and correct the condition? | -- | Go to Step 7 | Go to Step 6 | |||||||||||||||||||||
6 | Replace the HO2S 1. Refer to Heated Oxygen Sensor 1 Replacement . Did you complete the replacement? | -- | Go to Step 7 | -- | ||||||||||||||||||||
7 |
Did the DTC fail this ignition? | -- | Go to Step 2 | Go to Step 8 | ||||||||||||||||||||
8 | Observe the Capture Info with a scan tool. Are there any DTCs that have not been diagnosed? | -- | System OK | |||||||||||||||||||||
