P0138

DTC P0138

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 powertrain control module (PCM) supplies the HO2S with a reference, or bias, voltage of about 450 mV. When the engine is first started the PCM 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. If the PCM detects an HO2S voltage that stays above a specified value, DTC P0138 sets for HO2S bank 1 sensor 2, or DTC P0158 sets for HO2S bank 2 sensor 2.

CONDITIONS FOR RUNNING THE DTC

Without RPO JL4
DTC P0101, P0102, P0103, P0106, P0107, P0108, P0112, P0113, P0116, P0117, P0118, P0121, P0122, P0123, P0200, P0300, P0442, P0446, P0452, P0453, P0455, P0496, P1258 are not set.

With RPO JL4
DTC P0068, P0101, P0102, P0103, P0106, P0107, P0108, P0112, P0113, P0116, P0117, P0118, P0120, P0169, P0178, P0179, P0200, P0220, P0300, P0442, P0446, P0452, P0453, P0455, P0496, P1125, P1258, P1516, P2101, P2108, P2135, U0107 are not set.

Rich Test Enable:
- The Loop Status parameter is Closed.
- The Ignition 1 Signal parameter is between 10-18 volts.
- The Fuel Tank Level Remaining parameter is more than 10 percent.
- WITHOUT RPO JL4-The TP Sensor parameter is between 3-70 percent.
- WITH RPO JL4-The TP Indicated Angle parameter is between 3-70 percent more than the value observed at idle.

Decel Fuel Cutoff Test Enable:
- The Loop Status parameter is Closed.
- The Ignition 1 Signal parameter is between 10-18 volts.
- The Fuel Tank Level Remaining parameter is more than 10 percent.
- The Engine Run Time parameter is more than 30 seconds.
- The Decel. Fuel Cutoff parameter is active for more than 4 seconds.

CONDITIONS FOR SETTING THE DTC

Rich Test
The PCM detects that the affected HO2S voltage parameter is more than 950 mV for 200 seconds.

Decel Fuel Cutoff Test
The PCM detects that the affected HO2S voltage parameter is more than 480 mV for 5 seconds.

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

Steps 1 - 3:

Steps 4 - 7:

Steps 8 - 11:

Step 12:

Steps 13 - 18:

The number below refers to the step number on the diagnostic table.
2. If the voltage does not change more that the specified value, the condition is present.