P0131

DTC P0131

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 engine control module (ECM) supplies the HO2S with a reference, or bias, voltage of about 450 mV. When the engine is first started the ECM 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, and low HO2S voltage indicates a lean exhaust stream. If the ECM detects an HO2S 1 voltage that stays below a specified value, DTC P0131 will set.

DTC DESCRIPTOR
This diagnostic procedure supports the following DTC:
DTC P0131 Circuit Low Voltage Sensor 1

CONDITIONS FOR RUNNING THE DTC
- DTCs P0106, P0107, P0108, P0112, P0113, P0117, P0118, P0122, P0123, P0125, P0171, P0172, P0300, P0336, P0340, P0341, P0455, P0500, P0601, P0602, P0606, P0641, P0722, P0723 are not set.
- The Loop Status parameter is closed.
- The Air Fuel Ratio parameter is between 14.5:1 and 14.8:1.
- The transmission is in Drive with automatic transmission.
- DTC P0131 runs continuously when the above conditions are met.

CONDITIONS FOR SETTING THE DTC

Lean Test
- The ECM detects that the HO2S 1 voltage parameter is less than 291 mV.
- DTC P0131 sets during the lean test within 100 seconds when the above condition is met.

OR

Power Enrichment Test
- The ECM detects that the HO2S 1 voltage parameter is less than 291 mV.
- DTC P0131 sets during the power enrichment test within 10 seconds when the above condition is met.

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 1-7:

Steps 8-11:

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.