P0151

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 in Closed Loop. 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 provide an accurate voltage signal. If the PCM detects that the affected HO2S 1 voltage remains below a calibrated amount for an excessive amount of time, DTC P0131 or P0151 will set.

CONDITIONS FOR RUNNING THE DTC
- DTCs P0101, P0102, P0103, P0106, P0107, P0108, P0112, P0113, P0116, P0117, P0118, P0121, P0122, P0123, P0125, P0128, P0201-P0208, P0410, P0412, P0418, P0419, P0440, P0442, P0443, P0446, P0449, P1415, P1416, P1441 are not set.
- The system voltage is between 9-18 volts.
- The TP Sensor parameter is between 3-25 percent.
- The Loop Status parameter is closed.
- The Air Fuel Ratio parameter is between 14.5-14.8.
- The above conditions are met for 3 seconds.

CONDITIONS FOR SETTING THE DTC
The PCM detects that the HO2S 1 voltage is less than 75 mV for more than 5 seconds.

Or

The PCM detects that the HO2S 1 voltage is less than 575 mV during power enrichment (PE) mode for more than 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 1-2:

Step 3-6:

Step 7:

Step 8-13:

The numbers below refer to the step numbers on the diagnostic table.
6. When the affected high signal circuit is shorted to the heater low control circuit, the short to ground will change to a short to voltage with the key ON, and the engine OFF.
7. The conditions listed in the table may contribute to the failure of the HO2S. The conditions listed apply only to this type of failure.