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 0-1,000 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 within each HO2S heat the sensor. 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 two 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, the powertrain control module (PCM) will wait a calibrated amount of time and then begin the intrusive test. 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 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 P0136 will set.
Each HO2S 2 has the following circuits:
| • | An HO2S 2 high signal circuit |
| • | An HO2S 2 low signal circuit |
| • | An HO2S 2 heater ignition 1 voltage circuit |
| • | An HO2S 2 heater low control circuit |
Conditions for Running the DTC
DTCs P0030, P0036, P0101, P0102, P0103, P0107, P0108, P0112, P0113, P0117, P0118, P0120, P0125, P0130, P0131, P0133, P0134, P0135, P0140, P0141, P0201, P0202, P0203, P0204, P0205, P0206, P0220, P0442, P0443, P0446, P0449, P0455, P0496, P1133, P1134 are not set.
Passive Test
The engine is running for at least 6 seconds.
Intrusive Test
| • | The Engine Run Time parameter is more than 6.5 minutes. |
| • | The ignition voltage is between 9-18 volts. |
| • | The Engine Speed parameter is between 1,000-3,000 RPM. |
| • | The MAF Sensor parameter is between 14-50 g/s. |
| • | The Vehicle Speed parameter is between 32-128 kph (20-80 mph). |
| • | The evaporative emission (EVAP) purge diagnostic is not active. |
Conditions for Setting the DTC
- The HO2S 2 parameter is between 290-685 mV during the passive test.
- One of the following tests fail:
| • | Lean Intrusive Test |
| - | The PCM detects that the HO2S 2 voltage is more than 290 mV for 11.4 seconds. |
| - | The PCM detects that the HO2S 1 voltage is less than 100 mV. |
| • | Rich Intrusive Test |
| - | The PCM detects that the HO2S 2 voltage is less than 685 mV for 11.4 seconds. |
| - | The PCM detects that the HO2S 1 voltage is more than 777 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. |
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-Engine Controls? | -- | Go to Step 2 | |
2 |
Did the voltage vary above and below the specified range? | 290-685 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 voltage more than the specified value? | 800 mV | Go to Step 7 | Go to Step 5 |
5 | Is the voltage within the specified range? | 75-115 mV | Go to Step 14 | Go to Step 6 |
6 | Measure the voltage from the HO2S 2 high signal circuit, 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? | 0.2 V | Go to Step 8 | 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 , Wiring Repairs , and Heated Oxygen Sensor Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 16 | Go to Step 13 |
8 | Measure the voltage from the HO2S 2 low signal circuit, 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 12 | Go to Step 10 |
9 | Test the HO2S 2 high signal circuit for an open. Refer to Circuit Testing , Wiring Repairs , and Heated Oxygen Sensor Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 19 | Go to Step 13 |
10 |
Is the parameter less than the specified value? | 100 mV | Go to Step 15 | Go to Step 11 |
11 | Test the HO2S 2 low signal circuit for an open. Refer to Circuit Testing , Wiring Repairs , and Heated Oxygen Sensor Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 19 | Go to Step 16 |
12 | Test the HO2S 2 low signal circuit for a short to voltage. Refer to Circuit Testing , Wiring Repairs , and Heated Oxygen Sensor Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 19 | Go to Step 16 |
13 | Test the HO2S 2 high signal circuit for a short to ground or a short to the HO2S 2 low signal circuit. Refer to Circuit Testing , Wiring Repairs , and Heated Oxygen Sensor Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 19 | Go to Step 16 |
14 | Test the HO2S 2 high signal circuit for a short to the HO2S 2 heater low control circuit. Refer to Circuit Testing , Wiring Repairs , and Heated Oxygen Sensor Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 19 | Go to Step 16 |
15 | 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 19 | Go to Step 17 |
16 | Test for shorted terminals and poor connections 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 19 | Go to Step 18 |
17 |
Notice: Refer to Heated Oxygen Sensor Resistance Learn Reset Notice in the Preface section. Replace the HO2S 2. Refer to Heated Oxygen Sensor 2 Replacement . Did you complete the replacement? | -- | Go to Step 19 | -- |
18 | Replace the PCM. Refer to Powertrain Control Module Replacement . Did you complete the replacement? | -- | Go to Step 19 | -- |
19 |
Did the DTC fail this ignition? | -- | Go to Step 2 | Go to Step 20 |
20 | Observe the Capture Info with a scan tool. Are there any DTCs that have not been diagnosed? | -- | System OK | |
