P0138

DTC P0138

CIRCUIT DESCRIPTION
The secondary heated oxygen sensor (HO2S) measures the oxygen content of the exhaust downstream of the three-way catalyst (TWC), so that the TWC efficiency is optimized. The powertrain control module (PCM) supplies a voltage near 450 mV between the HO2S high signal circuit and the low reference circuit. The HO2S varies the voltage over a range from about 1,000 mV when the exhaust is rich, down through about 10 mV when the exhaust is lean.

The PCM monitors and stores the HO2S voltage information. The PCM evaluates the HO2S voltage samples in order to determine the amount of time that the HO2S voltage was out of range. The PCM compares the stored HO2S voltage samples taken within each sample period and determines if the majority of the samples are out of the operating range.

The PCM monitors the HO2S voltage for being fixed above a predetermined voltage. If the PCM detects the voltage is too high, this DTC sets.

DTC DESCRIPTORS
This diagnostic procedure supports the following DTCs:
- DTC P0138 HO2S Circuit High Voltage Bank 1 Sensor 2
- DTC P0158 HO2S Circuit High Voltage Bank 2 Sensor 2

CONDITIONS FOR RUNNING THE DTC
- DTCs P0030, P0050, P0107, P0108, P0112, P0113, P0117, P0118, P0133, P0135, P0137, P0141, P0153, P0155, P0157, P0161, P0171, P0172, P0174, P0175, P0300, P0301-P0306, P0335, P0401, P0404, P0442, P0443, P0496, P1128, P1129, P2413, P2414, and P2415 are not set.
- The engine is operating for more than 2 minutes.
- The engine speed is less than 2,350 RPM.
- The engine coolant temperature (ECT) is more than 69°C (156°F).
- The intake air temperature (IAT) is more than -13°C (8°F).
- The HO2S 1 same bank lambda is between 0.73-1.47.
- The fuel system is in closed loop.
- DTCs P0138 and P0158 run once per drive cycle when the above conditions are met.

CONDITIONS FOR SETTING THE DTC
- The PCM detects that the HO2S signal voltage is more than 1,250 mV.
- The condition exists for more than 5 seconds.

ACTION TAKEN WHEN THE DTC SETS
- The PCM illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
- The PCM records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the PCM stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the PCM records the operating conditions at the time of the failure. The PCM writes the conditions to the Freeze Frame and updates the Failure Records.

CONDITIONS FOR CLEARING THE MIL/DTC
- The PCM turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
- A last test failed, or current DTC, clears when the diagnostic runs and does not fail.
- A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
- Use a scan tool in order to clear the MIL and the DTC.

TEST DESCRIPTION

Steps 1-8:

Steps 9-14:

The numbers below refer to the step numbers in the diagnostic table.
1. The Diagnostic System Check - Vehicle prompts the technician to complete some basic checks and store the Freeze Frame data on the scan tool if applicable. This creates an electronic copy of the data taken when the fault occurred. The information is then stored in the scan tool for later reference.
2. This step verifies that a condition exists.
4. This step tests the signal circuit of the HO2S 2. Test the signal circuit for a short to voltage, if the voltage on the signal circuit is more than the specified value.
5. This step isolates the condition. If the voltage on the signal circuit is more than the specified value after the PCM is disconnected, test the signal circuit for a wire to wire short to a voltage.
6. This step isolates the condition. If the test lamp illuminates when the HO2S 2 heater is commanded ON, test the signal circuit for a short to the heater control circuit