O2 Sensors

[npituley]

I have a sierra 07 classic 4x4 with a 5.3. It has 43000 miles. I purchased truck only months ago, while test driving the service engine light comes on. I tell dealer to fix and I will buy truck, he replaces sensor and light comes back on days later. This happens 3 times and dealer tells me he replaces all 4 of the o2 sensors. Now I have put around 3000 miles and light comes back on! I hook up my obd 2 reader and it says P2A04 which from what I understand is o2 sensor, bank 2 row 2. Could there be some bigger issue here that I am getting these codes or is it possible I am dealing with faulty sensors all the time. I would like to get this problem fixed once and for all.

[npituley]

Did I post this wrong or is it that none of you have any ideas????

[txab]

DTC P2A04

 

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 less than 349 mV and greater than 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 less than 349 mV or greater than 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 Performance Bank 1 Sensor 2

DTC P2A04 HO2S Performance Bank 2 Sensor 2

CONDITIONS FOR RUNNING THE DTC

DTCs P0030, P0036, P0050, P0053, P0054, P0056, P0059, P0060, P0101, P0102, P0103, P0106, P0107, P0108, P0112, P0113, P0117, P0118, 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 above conditions are met for 2 seconds .

This diagnostic runs one time per drive cycle when the above conditions are met.

Intrusive Test

 

 

The engine run time is more than 218 seconds .

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 -4 and +4 percent .

The maximum number of intrusive attempts is less than 100.

The above conditions are met for 3 seconds .

This diagnostic runs one time per drive cycle when the above conditions are met.

CONDITIONS FOR SETTING THE DTC

 

 

The PCM detects that the HO2S bank 1 sensor 2 or HO2S bank 2 sensor 2 did not transition less than 349 mV and greater than 710 mV during the passive test.

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 greater than 349 mV for 60 seconds .

The HO2S bank 1 sensor 1 and HO2S bank 2 sensor 1 is less than 300 mV .

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 greater 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.