P0144

Circuit Description
The PCM provides a 0.45 volt reference signal to the oxygen sensor on CKT 1668. 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. DTC P0144 is designed so that if the oxygen sensor stays at a rich voltage for 100 out of 120 seconds during the test conditions, this DTC will set. DTC P0144 will set when:
^ There is an oxygen sensor circuit fault giving a false rich indication;
^ The air fuel ratio is actually rich due to a fuel control or emission system fault.

Conditions for Running the DTC
^ DTCs P0101, P0102, P0103, P0107, P0108, P0117, P0118, P0121, P0122, P0123, P0131, P0132, P0133, P0134, P0151, P0152, P0153, P0154, P0300, P1133, P1134, P1153 and P1154 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 sensors ready.
^ Engine speed 800 RPM or greater.
^ MAP sensor greater than 32 kPa.
^ Above conditions met for 5 seconds.

Conditions for Setting the DTC
Oxygen sensor has been rich (900 mV (0.9V) or greater) for 100 out of 120 seconds.

Action Taken When the DTC Sets
^ 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. It both banks were rich, inspect for a condition that would cause rich engine operation.

Test Description
Number(s) below refer to the step number(s) on the Diagnostic Table.
2. if DTC P0146 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 below 0.9 volt. A rich sensor/condition will cause the voltage to remain above 0.9 volt.
4. Checking for proper oxygen sensor operation. The voltage should fluctuate below 0.9 volt.