Circuit Description
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 vehicle 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 0-1,100 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 1,100 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 within each HO2S heat the sensor. The powertrain control module (PCM) controls the HO2S heater control circuit. The HO2S heater diagnostic monitors the current draw through the HO2S output driver module (ODM) when the engine is running. This allows the system to enter Closed Loop earlier and the control module to calculate the air-to-fuel ratio sooner.
The HO2S 2 is used for catalyst monitoring. This diagnostic runs once per ignition cycle. This diagnostic has 2 phases for running the DTC, a passive test and an intrusive test. If the HO2S 2 voltage transitions below 290 mV and above 685 mV during the passive test, the DTC will pass for this ignition cycle. If the DTC does not pass during the passive test and too much time has elapsed since startup, the intrusive test will begin. The control module will adjust the air-to-fuel ratio during the intrusive test. As the air-to-fuel ratio is adjusted to rich and/or lean, the control module waits for a predicted response from the HO2S 2.
If the HO2S 2 voltage transitions below 290 mV and/or above 685 mV, the diagnostic will pass for this ignition cycle. If the control module does not receive the expected response from the HO2S 2, DTC P2A01 will set.
The HO2S 2 has the following circuits:
| • | A HO2S 2 high signal circuit |
| • | A HO2S 2 low reference circuit |
| • | A HO2S 2 heater ignition voltage circuit |
| • | A HO2S 2 heater low control circuit |
DTC Descriptor
This diagnostic procedure supports the following DTC:
DTC P2A01 HO2S Performance Bank 1 Sensor 2
Conditions for Running the DTC
This vehicle uses 2 test methods to run this DTC. They are Passive test and Intrusive test.
Passive Test
To enable the passive test, the following conditions must be met:
| • | DTCs P0030, P0036, P0101, P0102, P0103, P0107, P0108, P0112, P0113, P0117, P0118, P0121, P0122, P0123, P0125 (where applicable), P0131, P0132, P0133, P0134, P0135, P0137, P0138, P0140, P0141, P0201, P0202, P0203, P0204, P0205, P0206, P0442, P0443, P0446, P0449, P0455, P0496, P1133, P1134, P2A00 are not set. |
| • | The system voltage is between 9-18 volts. |
| • | The engine is running for at least 6 seconds. |
Intrusive Test
To enable the Intrusive test, the following conditions must be met:
| • | The passive test did not report a pass. |
| • | The engine run time is more than 6.5 minutes. |
| • | The engine speed is between 1,000-3,000 RPM. |
| • | The MAF sensor parameter is between 14-50 g/s. |
| • | The vehicle speed is between 32-128 km/h (20-80 mph). |
| • | Loop Status parameter is Closed. |
| • | The evaporative emission (EVAP) purge valve solenoid remains at 0 percent. |
Conditions for Setting the DTC
| • | The HO2S 2 voltage remains between 290 mV and 685 mV 6.5 minutes during the passive test. |
| • | The HO2S 2 cannot achieve a voltage above 685 mV 11.4 seconds and/or below 290 mV for 11.4 seconds. during the intrusive test. |
| • | This diagnostic runs once per trip. |
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. |
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
Schematic Reference: Engine Controls Schematics Connector End View Reference: Engine Controls Connector End Views or Powertrain Control Module Connector End Views | ||||
1 | Did you perform the Diagnostic System Check - Vehicle? | -- | Go to Step 2 | Go to Diagnostic System Check - Vehicle in Vehicle DTC Information |
2 | Is DTC P0138 or DTC P0140 also set? | -- | Go to Step 3 | |
3 |
Did the voltage vary above and below the specified range? | 290-685 mV | Go to Step 4 | Go to Step 5 |
4 |
Did the DTC fail this ignition? | -- | Go to Step 5 | Go to Intermittent Conditions |
5 |
Is the voltage more than the specified value? | 5 V | Go to Step 9 | Go to Step 6 |
6 |
Is the voltage more than the specified value? | 410 mV | Go to Step 10 | Go to Step 7 |
7 | With the jumper wire from the previous step still connected, observe the HO2S 2 parameter with a scan tool. Is the voltage less than the specified value? | 15 mV | Go to Step 11 | Go to Step 8 |
8 |
Is the voltage less than the specified value? | 15 mV | Go to Step 13 | Go to Step 12 |
9 | Test the HO2S 2 low signal circuit for a short to voltage. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 17 | Go to Step 14 |
10 | Test the HO2S 2 low 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 17 | Go to Step 14 |
11 | Test the HO2S 2 high signal circuit for a short to ground. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 17 | Go to Step 14 |
12 | Test the HO2S 2 high 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 17 | Go to Step 14 |
13 | Test for an intermittent and for a poor connection at the HO2S 2. Refer to Testing for Intermittent Conditions and Poor Connections , Connector Repairs , and Heated Oxygen Sensor Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 17 | Go to Step 15 |
14 | Test for an intermittent and for a poor connection at the powertrain control module (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 17 | Go to Step 16 |
15 | Replace the HO2S 2. Refer to Heated Oxygen Sensor 2 Replacement . Did you complete the replacement? | -- | Go to Step 17 | -- |
16 | Replace the PCM. Refer to Control Module References in Computer/Integrating Systems for replacement, setup, and programming. Did you complete the replacement? | -- | Go to Step 17 | -- |
17 |
Did the DTC fail this ignition? | -- | Go to Step 2 | Go to Step 18 |
18 | Observe the Capture Info with a scan tool. Are there any DTCs that have not been diagnosed? | -- | Go to Diagnostic Trouble Code (DTC) List - Vehicle in Vehicle DTC Information | System OK |
