P2A01

DTC P2A01

CIRCUIT DESCRIPTION
Heated oxygen sensors (HO2S) are used for fuel control and post catalyst monitoring. Each HO2S compares the oxygen content of the surrounding air with the oxygen content in the exhaust stream. The HO2S must reach operating temperature to provide an accurate voltage signal. Heating elements inside the HO2S minimize the time required for the sensors to reach operating temperature. The powertrain control module (PCM) supplies the HO2S with a reference, or bias, voltage of about 450 mV. When the engine is first started the PCM operates in open loop, ignoring the HO2S voltage signal. Once the HO2S reaches operating temperature and closed loop is achieved, the HO2S generates a voltage within a range of 0-1,000 mV that fluctuates above and below bias voltage. High HO2S voltage indicates a rich exhaust stream; low HO2S voltage indicates a lean exhaust stream.

The HO2S bank 1 sensor 2 and HO2S bank 2 sensor 2 are used for catalyst monitoring. This diagnostic runs once per ignition cycle. This diagnostic consists of two tests, a passive test and an intrusive test. During the passive test, if the HO2S bank 1 sensor 2 or HO2S bank 2 sensor 2 voltage transitions below 349 mV and above 710 mV, the DTC will pass for this ignition cycle. If the DTC does not pass during the passive test, the intrusive test will begin. During the intrusive test, the control module will force the air-to-fuel ratio rich and/or lean. The control module then waits for a predicted response from the HO2S. If the HO2S voltage transitions below 349 mV and/or above 710 mV, the DTC will pass for this ignition cycle. If the control module does not receive the expected response from the HO2S, DTC P2A01 will set for HO2S bank 1 sensor 2 or DTC P2A04 will set for HO2S bank 2 sensor 2.

DTC DESCRIPTORS
This diagnostic procedure supports the following DTCs:
- DTC P2A01 HO2S Circuit Bank 1 Sensor 2
- DTC P2A04 HO2S Circuit Bank 2 Sensor 2

CONDITIONS FOR RUNNING THE DTC
DTCs P0053, P0054, P0059, P0060, P0101, P0102, P0103, P0106, P0107, P0108, P0112, P0113, P0117, P0118, P0125, P0128, P0131, P0132, P0133, P0134, P0135, P0137, P0138, P0140, P0141, P0151, P0152, P0153, P0154, P0155, P0157, P0158, P0160, P0161, P0200, P0442, P0443, P0446, P0449, P0455, P0496, P1133, P1134, P1153, P1154 are not set.

Passive Test
- The engine is running.
- The Engine Run Time parameter is less than 13.5 minutes.
- This diagnostic runs one time per drive cycle once the above conditions are met.

Intrusive Test
- The Engine Run Time parameter is more than 13.5 minutes.
- The Ignition 1 Signal parameter is between 10-18 volts.
- The Engine Speed parameter is between 900-5,000 RPM.
- The MAF Sensor parameter is between 5-100 g/s.
- The Vehicle Speed parameter is between 24-131 km/h (15-82 mph).
- The Short Term FT Bank 1 and Bank 2 parameter is between -10 and +10 percent.
- The maximum number of intrusive attempts is less than 100.
- This diagnostic runs one time per drive cycle once the above conditions are met.

CONDITIONS FOR SETTING THE DTC
1. This diagnostic concludes within 15.5 minutes.
2. The PCM detects that the HO2S bank 1 sensor 2 or HO2S bank 2 sensor 2 did not transition below 349 mV and above 710 mV during the passive test.
3. One of the following tests fail:
- Lean Intrusive Test
- The PCM detects that the HO2S bank 1 sensor 2 or HO2S bank 2 sensor 2 is more than 349 mV for 60 seconds.
- The HO2S bank 1 sensor 1 and HO2S bank 2 sensor 1 is less than 300 mV.OR
- Rich Intrusive Test
- The PCM detects that the HO2S bank 1 sensor 2 or HO2S bank 2 sensor 2 is less than 710 mV for 60 seconds.
- The HO2S bank 1 sensor 1 and HO2S bank 2 sensor 1 is more than 600 mV.

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

Steps 1-10:

Steps 11-18:

Steps 19-21:

The number below refers to the step number on the diagnostic table.
2. If the voltage does not change more than the specified value, the condition is present.