Circuit Description
The heated oxygen sensor (HO2S) produces a voltage that varies between 100-900 mV under normal operating conditions. The engine control module (ECM) produces a bias voltage on the HO2S signal circuit of 420-480 mV. The reference ground for the sensor is provided through the ECM. The ECM monitors the signal voltage to determine if the exhaust is lean or rich. The oxygen sensor voltage is high when the exhaust is rich, and low when the exhaust is lean. The ECM constantly monitors the HO2S signal during the Closed Loop operation. If the ECM forces a lean or rich condition and detects an HO2S voltage that is not properly correlated to the commanded rich or lean state, DTC P0139 will set for bank 1 sensor 2, or DTC P0159 will set for bank 2 sensor 2.
Conditions for Running the DTC
| • | The bank 1 sensor 2 or bank 2 sensor 2 loop status is closed |
| • | The Battery Voltage parameter is more than 11 volts. |
| • | The calculated catalytic converter temperature is less than 800°C (1,472°F). |
Conditions for Setting the DTC
| • | The ECM detects that the HO2S parameter is stuck above or below 350 mV for longer than 110 seconds. |
| OR |
| • | The ECM detects that the HO2S parameter is more than 200 mV for longer than 5 seconds during a decel fuel cutoff condition. |
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 | Values | Yes | No | ||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Schematic Reference: Engine Controls Schematics Connector End View Reference: Engine Controls Connector End Views | ||||||||||||||||
1 | Did you perform the Diagnostic System Check-Engine Controls? | -- | Go to Step 2 | |||||||||||||
2 |
Does the affected HO2S voltage parameter react instantly to the above action? | -- | 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 voltage parameter above the specified value? | 525 mV | Go to Step 5 | Go to Step 7 | ||||||||||||
5 | Measure the voltage from the HO2S 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? | 50 mV | Go to Step 9 | Go to Step 6 | ||||||||||||
6 | Measure the voltage from the HO2S 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? | 550 mV | Go to Step 10 | Go to Step 14 | ||||||||||||
7 |
Is the voltage less than the specified value? | 25 mV | Go to Step 8 | Go to Step 11 | ||||||||||||
8 |
Is the voltage less than the specified value? | 25 mV | Go to Step 13 | Go to Step 12 | ||||||||||||
9 | Test the HO2S low signal circuit for a short to voltage or a short to the heater low control circuit. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 17 | Go to Step 14 | ||||||||||||
10 | Test the HO2S high signal circuit for a short to voltage or a short to the heater low control circuit. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 17 | Go to Step 14 | ||||||||||||
11 | Test the HO2S 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 17 | Go to Step 14 | ||||||||||||
12 | Test the HO2S 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 17 | Go to Step 14 | ||||||||||||
13 | The HO2S 2 is detecting a rich or lean exhaust condition or may be contaminated. Inspect for one of the following conditions:
Repair any of the above or similar engine conditions as necessary. Did you find and correct the condition? | -- | Go to Step 17 | Go to Step 15 | ||||||||||||
14 | Test for shorted terminals and 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 17 | Go to Step 16 | ||||||||||||
15 | Replace the affected HO2S. Refer to Heated Oxygen Sensor Replacement - Bank 1 Sensor 2 or Heated Oxygen Sensor Replacement - Bank 2 Sensor 2 . Did you complete the replacement? | -- | Go to Step 17 | -- | ||||||||||||
16 | Replace the ECM. Refer to Engine Control Module Replacement . Did you complete the replacement? | -- | Go to Step 17 | -- | ||||||||||||
17 |
Did the DTC fail this ignition? | -- | Go to Step 2 | Go to Step 18 | ||||||||||||
18 | Observe the Capture Info with a scan tool. Are there any DTCs that have not been diagnosed? | -- | System OK | |||||||||||||
