P0151

Diagnostic Chart:

Wiring Diagram:

CIRCUIT DESCRIPTION

The PCM provides a 0.45 volt reference signal to the oxygen sensor on CKT 412. 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 P0151 is designed so that if the oxygen sensor stays at a lean voltage for more than 40 seconds during the test conditions, this DTC will set. DTC P0151 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, P0152 and P0154 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.

^ Above conditions met for 3 seconds.

^ DTC P0131 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 it DTC P0131, P0132 or P0134 is also set.

^ Transaxle shift adapts maintained at current levels.

^ PCM disables Closed Loop and long term fuel trim operation if DTC P0131, P0132, or P0134 is also set.

^ PCM uses rear oxygen sensor feedback for Closed Loop and long term fuel trim operation if DTC P0131, P0132, and P0134 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 tails. 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.

^ PCM battery voltage is interrupted.

^ Using a Scan tool.

DIAGNOSTIC AIDS

NOTICE: Refer to HO2S wire repair notice in Service Precautions.

Check snapshot data for front and rear long term fuel trim values. If both banks were lean, check for a condition that would cause lean engine operation. If just the front bank was lean, check for a condition that would only cause the front bank to be lean, such as an intermittent short to ground on CKT 412.

TEST DESCRIPTION

Number(s) below refer to the step number(s) on the Diagnostic Table.

2. If DTC P0154 is also set, diagnose it first because an oxygen sensor not ready can cause other emission related problems.

3. 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.

4. If the vehicle runs out of fuel, this DTC could set.

5. Checking for proper operation of the front cylinder bank oxygen sensor.