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 engine control module (ECM) supplies the HO2S with a reference, or bias, voltage of about 450 mV. When the engine is first started, the ECM 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 2 is 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 2 voltage transitions below 300 mV and above 725 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 300 mV and/or above 725 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 .
DTC Descriptor
This diagnostic procedure supports the following DTC:
DTC P2A01 HO2S Circuit Sensor 2
Conditions for Running the DTC
DTCs P0068, P0106, P0107, P0108, P0112, P0113, P0117, P0118, P0120, P0122, P0123, P0125, P0128, P0130, P0131, P0132, P0137, P0138, P0140, P0141, P0171, P0201-P0204, P0220, P0300, P0315, P0336, P0442, P0446, P0452, P0453, P0455, P0496, P0506, P0507, P0601, P0602, P0604, P0606, P0641, P0651, P1134, P1516, P1621, P1680, P1681, P2101, P2120, P2125, P2135, P2138, P2176 are not set.
Passive Test
| • | The engine is running. |
| • | The Engine Run Time parameter is less than 13.3 minutes. |
Intrusive Test
| • | The Engine Run Time parameter is more than 13.3 minutes. |
| • | The ignition 1 Signal parameter is between 11-18 volts. |
| • | The Engine Speed parameter is between 1,000-5,000 RPM. |
| • | The Vehicle Speed parameter is between 32-128 km/h (20-80 mph). |
| • | The Short Term FT parameter is between -10 and +10 percent. |
| • | The Air Flow Calculated parameter is between 14-100 g/s. |
| • | The maximum number of intrusive attempts is less than 25. |
| • | DTC P2A01 runs continuously when the above conditions have been met for one second. |
Conditions for Setting the DTC
- The ECM detects that the HO2S 2 did not transition below 300 mV and above 725 mV during the passive test.
- One of the following tests fail:
| • | The lean intrusive test |
| - | The ECM detects that the HO2S 2 is more than 300 mV for 12 seconds. |
| - | The HO2S 1 is less than 300 mV. |
| - | OR |
| • | The rich intrusive test |
| - | The ECM detects that the HO2S 2 is less than 725 mV for 12 seconds. |
| - | The HO2S 1 is more than 600 mV. |
DTC P2A01 sets within 60 seconds when the above conditions are met.
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 number below refers to the step number on the diagnostic table.
Step | Action | Value(s) | Yes | No | ||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Schematic Reference: Engine Controls Schematics Connector End View Reference: Engine Controls Connector End Views or Engine 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 | ||||||||||||||
Did the HO2S 2 voltage parameter change more than the specified value? | 200 mV | Go to Step 3 | Go to Step 4 | |||||||||||||||
3 |
Did the DTC fail this ignition? | -- | Go to Step 4 | Go to Intermittent Conditions | ||||||||||||||
4 |
Is the HO2S 2 voltage parameter less than the specified value? | 100 mV | Go to Step 6 | Go to Step 5 | ||||||||||||||
5 | Observe the HO2S 2 voltage parameter with a scan tool. Is the HO2S 2 voltage parameter more than the specified value? | 800 mV | Go to Step 7 | Go to Step 8 | ||||||||||||||
6 | 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 21 | Go to Step 9 | ||||||||||||||
7 |
Important: The sensor may be damaged if the circuit is shorted to a voltage source. Test the HO2S 2 high 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 21 | Go to Step 18 | ||||||||||||||
8 | Measure the voltage from the low signal circuit of the HO2S 2 harness connector on the engine harness side to a good ground with a DMM. Refer to Circuit Testing in Wiring Systems. Is the voltage more than the specified value? | 2 V | Go to Step 10 | Go to Step 11 | ||||||||||||||
9 | Test the HO2S 2 high signal circuit for a short to the HO2S 2 low signal circuit. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 21 | Go to Step 18 | ||||||||||||||
10 | 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 21 | Go to Step 18 | ||||||||||||||
11 |
Is the HO2S 2 voltage parameter less than the specified value? | 100 mV | Go to Step 12 | Go to Step 14 | ||||||||||||||
12 |
Is the HO2S 2 voltage parameter less than the specified value? | 100 mV | Go to Step 15 | Go to Step 13 | ||||||||||||||
13 | Test the HO2S 2 low signal circuit for an open or high resistance. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 21 | Go to Step 18 | ||||||||||||||
14 | Test the HO2S 2 high signal circuit for an open or high resistance. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 21 | Go to Step 18 | ||||||||||||||
15 | Test the HO2S 2 heater low control circuit for a short to the HO2S 2 high signal circuit or HO2S 2 low signal circuit. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 21 | Go to Step 16 | ||||||||||||||
16 |
Notice: Refer to Silicon Contamination of Heated Oxygen Sensors Notice in the Preface section.
Did you find and correct the condition? | -- | Go to Step 21 | Go to Step 17 | ||||||||||||||
17 | Test for shorted terminals and for poor connections at the HO2S 2. 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 21 | Go to Step 19 | ||||||||||||||
18 | Test for shorted terminals and for poor connections at the engine control module (ECM). 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 21 | Go to Step 20 | ||||||||||||||
19 | Replace the HO2S 2. Refer to Heated Oxygen Sensor 2 Replacement . Did you complete the replacement? | -- | Go to Step 21 | -- | ||||||||||||||
20 | Replace the ECM. Refer to Control Module References in Computer/Integrating Systems for replacement, setup, and programming. Did you complete the replacement? | -- | Go to Step 21 | -- | ||||||||||||||
21 |
Did the DTC fail this ignition? | -- | Go to Step 2 | Go to Step 22 | ||||||||||||||
22 | 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 | ||||||||||||||
