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 of the exhaust stream. When the vehicle is first started, the powertrain control module (PCM) operates in an Open Loop mode, ignoring the HO2S signal voltage when calculating the air-to-fuel ratio. The PCM supplies the HO2S with a reference, or bias, voltage of about 450 mV. The HO2S generates a voltage within a range of 0-1,000 mV that fluctuates above and below bias voltage once the sensor reaches operating temperature. A high HO2S voltage output indicates a rich fuel mixture. A low HO2S voltage output indicates a lean mixture. Heating elements inside the HO2S minimize the time required for the sensors to reach operating temperature, and to provide an accurate voltage signal.
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 286 mV and above 703 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 lean, the control module waits for a predicted response from the HO2S 2. If the HO2S 2 voltage transitions below 286 mV and above 703 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 1 has the following circuits:
| • | An HO2S 2 high signal circuit |
| • | An HO2S 2 low signal circuit |
| • | An HO2S 2 heater ignition voltage circuit |
| • | An HO2S 2 heater low control circuit |
| • | An HO2S low reference circuit |
Conditions for Running the DTC
DTCs P0036, P0101, P0102, P0103, P0107, P0108, P0112, P0113, P0117, P0118, P0121, P0122, P0123, P0130, P0131, P0132, P0133, P0134, P0135, P0140, P0141, P0201, P0202, P0203, P0204, P0205, P0206, P0442, P0443, P0446, P0449, P0455, P0496, P1133, P1134 are not set.
Passive Test
| • | The engine is running. |
| • | The engine run time is less than 6.5 minutes. |
Intrusive Test
| • | DTC P0401 is not commanding fuel. |
| • | The Engine Run Time parameter is more than 6.5 minutes. |
| • | The evaporative emission (EVAP) purge diagnostic is not active. |
| • | The Engine Speed parameter is between 1,000-3,000 RPM. |
| • | The MAF Sensor parameter is between 13-55 g/s. |
| • | The Vehicle Speed Sensor parameter is between 32-128 km/h (20-80 mph). |
| • | The ignition voltage is between 9-18 volts. |
| • | The above conditions have been met for 2.5 seconds. |
Conditions for Setting the DTC
The HO2S 2 is between 286-703 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 286 mV for 14 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 703 mV for 14 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? | 286-703 mV | Go to Step 4 | Go to Step 3 |
3 | Observe the HO2S 1 parameter with a scan tool. Is the voltage fluctuating rapidly above and below the specified range? | 286-703 mV | Go to Step 5 | Go to Step 9 |
4 |
Did the DTC fail this ignition? | 800 mV | Go to Step 4 | Go to Intermittent Conditions |
5 |
Is the voltage less than the specified value? | 25 mV | Go to Step 8 | Go to Step 6 |
6 | Probe the HO2S 2 low signal circuit, on the engine harness side, with a test lamp that is connected to B+. Refer to Probing Electrical Connectors in Wiring Systems. Does the test lamp illuminate? | -- | Go to Step 7 | Go to Step 12 |
7 |
Is the resistance more than the specified value? | 5 ohms | Go to Step 13 | Go to Step 10 |
8 | 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 16 | Go to Step 11 |
9 | Test the HO2S low reference circuit for an open or high resistance. 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 11 |
10 | 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 16 | Go to Step 14 |
11 | Test for shorted terminals and poor connections at the 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 16 | Go to Step 15 |
12 | Repair the open or high resistance in the HO2S 2 low signal circuit between the HO2S 2 connector and the splice. Refer to Wiring Repairs and Heated Oxygen Sensor Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 16 | -- |
13 | Repair the open or high resistance in the HO2S 2 low signal circuit between the PCM connector and the splice. Refer to Wiring Repairs and Heated Oxygen Sensor Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 16 | -- |
14 | Replace the HO2S 2. Refer to Heated Oxygen Sensor 2 Replacement . Did you complete the replacement? | -- | Go to Step 16 | -- |
15 | Replace the PCM. Refer to Powertrain Control Module Replacement . Did you complete the replacement? | -- | Go to Step 16 | -- |
16 |
Did the DTC fail this ignition? | -- | Go to Step 2 | Go to Step 17 |
17 | Observe the Capture Info with a scan tool. Are there any DTCs that have not been diagnosed? | -- | System OK | |
