P0131

Circuit Description
The PCM provides a 0.45 volt reference signal to the oxygen sensor on CKT 1666. When the oxygen sensor is cold, below 200°C (392°F), the oxygen sensor signal voltage will be around 0.45 volt and the PCM will keep the system in Open Loop operation. When the oxygen sensor is warm, above 200°C (392°F), the oxygen sensor will swing from rich to lean rapidly, if the PCM is in good control of the air fuel mixture. DTC P0131 is designed so that if the oxygen sensor stays at a lean voltage for more than 40 seconds during the test conditions, DTC P0131 will set. DTC P0131 will set when:
^ There is an oxygen sensor circuit fault giving a false lean indication.
^ The air fuel ratio is actually lean due to a vacuum leak or fuel control system fault.

Conditions for Running the DTC
^ DTCs P0101, P0102, P0103, P0107, P0108, P0117, P0118, P0121, P0122, P0123, P0132, and P0134, not set.
^ TP sensor between 5.4 and 25 degrees.
^ Coolant temperature 81.5°C (179°F) or greater.
^ Closed loop fuel control enabled.
^ Oxygen sensor ready.
^ Engine speed 800 RPM or greater.
^ MAP sensor greater than 32 kPa.
^ Conditions above met for 3 seconds.
^ DTC 151 test runs and passes.

Conditions for Setting the DTC
Oxygen sensor has been lean (356 mV (0.356V) or less) for 40 seconds out of 50 seconds.

Action Taken When the DTC Sets
^ PCM enables Evaporative Emission (EVAP) control solenoid if DTC P0151, P0152, or P0154 is also set.
^ Transaxle shift adapts maintained at current levels.
^ PCM disables Closed Loop and long term fuel trim operation if DTC P0151, P0152, or P0154 is also set.
^ PCM uses front oxygen sensor feedback for Closed Loop and long term fuel trim operation if DTC P0151, P0152, and P0154 are not set.
^ The PCM will illuminate the Malfunction Indicator Lamp (MIL) when the diagnostic runs and fails.
^ The PCM will record operating conditions at the time the diagnostic fails. This information will be stored in the Freeze Frame and Failure Records.

Conditions for Clearing the MIL/DTC
^ The PCM will turn the MIL OFF after three consecutive drive trips that the diagnostic runs and does not fail.
^ A Last Test Failed (current) DTC will clear when the diagnostic runs and does not fail
^ A History DTC will clear after forty consecutive warm-up cycles with no failures of any emission related diagnostic test.
^ Use a scan tool to clear DTCs.
^ Interrupting PCM battery voltage may or may not clear DTCs. This practice is not recommended.

Diagnostic Aids

Notice: Refer to HO2S wire repair notice in Oxygen Sensor. Service and Repair

Inspect snapshot data for front and rear long term fuel trim values. If both banks were lean, inspect for a condition that would cause lean engine operation. If just the rear bank was lean, inspect for a condition that would only cause the rear bank to be lean, such as an intermittent short to ground on CKT 1666.

Test Description
Number(s) below refer to the step number(s) on the Diagnostic Table.
2. If DTC P0134 is also set, diagnose it first because an oxygen sensor not ready can cause other emission related problems.
3. If the vehicle runs out of fuel, this DTC could set.
4. If the oxygen sensor is operating correctly, voltage will fluctuate above 0.3 volt. A lean sensor condition will cause the voltage to remain below 0.3 volt.