P0151

DTC 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 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 below a specified value, DTC P0131 sets for HO2S bank 1 sensor 1, DTC P0151 sets for HO2S bank 2 sensor 1.

DTC DESCRIPTORS
This diagnostic procedure supports the following DTCs:
- DTC P0131 HO2S Circuit Low Voltage Bank 1 Sensor 1
- DTC P0151 HO2S Circuit Low Voltage Bank 2 Sensor 2

CONDITIONS FOR RUNNING THE DTC

Lean Test Enable:
- DTCs P0101, P0102, P0103, P0106, P0107, P0108, P0112, P0113, P0116, P0117, P0118, P0121, P0122, P0123, P0200, P0442, P0446, P0452, P0453, P0455, P0496 are not set.
- 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 Throttle Position (TP) Sensor parameter is between 3-70 percent.
- The above conditions are met for 2 seconds.
- This diagnostic runs continuously once the above conditions are met.

OR

Power Enrichment Test Enable:
- DTCs P0101, P0102, P0103, P0106, P0107, P0108, P0112, P0113, P0116, P0117, P0118, P0121, P0122, P0123, P0200, P0442, P0446, P0452, P0453, P0455, P0496 are not set.
- 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 Power Enrichment parameter is active for more than 1 second.
- This diagnostic runs continuously once the above conditions are met.

CONDITIONS FOR SETTING THE DTC

Lean Test:
The PCM detects that the affected HO2S Voltage parameter is less than 200 mV for 165 seconds.

OR

Power Enrichment Test:
The PCM detects that the affected HO2S Voltage parameter is less than 360 mV for 10 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.
- The control module commands the Loop Status open.

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 - 9:

Steps 10 - 16:

The number below refers to the step number on the diagnostic table.
2. If the voltage is varying above and below the specified range, the condition is not present.