P0144

CIRCUIT DESCRIPTION
The VCM supplies a voltage of about 0.45 volt (450 mV) between the HO2S High and the HO2S Low circuits. (If measured with a 10 megohm digital voltmeter, this may read as low as 0.32 volt.) The heated oxygen sensor varies the voltage within a range of between about 1.0 volt (1000 mV) if the exhaust is rich, to about 0.10 volt (100 mV) if exhaust is lean.

The sensor is like an open circuit and produces no voltage when it is below about 360°C (600°F). The P0144 determines if the HO2S or the circuit is shorted to high by checking for a rich condition during steady throttle and Decel fuel cutoff (DFCO). This DTC is a type B DTCs.

CONDITIONS FOR SETTING THE DTC
The following conditions will set the DTC:

^ No TP sensor DTCs.
^ No Evaporative Emissions (EVAP) DTCs.
^ No IAT sensor DTCs.
^ No MAP sensor DTCs.
^ No ECT sensor DTCs.
^ No MAF sensor DTCs.
^ No intrusive test in progress.
^ No device controls active.
^ The system voltage measures at least 9.0 volts.

Test Enable Rich Test

^ A Closed Loop.
^ The air to fuel ratio is greater than 14.5 but less than 14.8.
^ The throttle position is greater than 0% but less than 50%.
^ The above met for 5 seconds.
^ The HO2S (Bank I, Sensor 3) DTCs are not active since the code clear.
^ The HO2S (Bank 1, Sensor 3) voltage is greater than 0.993V.

Test Enable DFCO Rich Test

1. Decel Fuel Cutoff mode active.
2. A Closed Loop.
3. Time elapsed since test enable is at least 2 seconds.
4. The HO2S voltage is greater than 0.468 V.

ACTION TAKEN WHEN THE DTC SET
A current DTC P0144 causes the system to operate in an Open Loop. With a current DTC P0144 set, the MIL (Malfunction Indicator Lamp) illuminates after 2 test failures.

CONDITIONS FOR CLEARING THE MIL/DTC
The VCM turns the MIL off after 3 consecutive driving trips without a fault condition present. A history DTC will clear if no fault conditions have been detected for 40 warm-up cycles (coolant temperature has risen 40°F from the start-up coolant temperature and the engine coolant temperature exceeds 160°F during that same ignition cycle) or the scan tool clearing feature has been used.

DIAGNOSTIC AIDS
Check the following items:

^ The fuel pressure: If the pressure is too high, the system will run rich. The VCM can compensate for some increase; however, if the pressure gets too high, the DTC may set. Refer to Fuel System Pressure Test.
^ A rich injector. Perform a poppet nozzle test. Refer to Fuel Injector Balance Test.
^ A leaking injector. Refer to Fuel Injector Balance Test.
^ Fuel contaminated oil.
^ Evaporative Emissions (EVAP) canister purge: Check for a fuel saturation. If full of fuel, check the canister control and hoses.
^ Leaking fuel pressure regulator diaphragm by checking the vacuum line to the regulator for fuel.
^ The TP sensor: An intermittent TP sensor output causes the system to run rich due to a false indication of the throttle moving.
^ False rich indication due to silicon contamination of the heated oxygen sensor. A DTC P0144 accompanied by a lean driveability conditions and a powdery white deposit on the sensor indicates a false rich indication.
^ Faulty HO2S: the HO2S (Bank 1, Sensor 3) is internally shorted, the HO2S (Bank 1, Sensor 3) voltage displayed on a scan tool will be over 1.0 volt (1000 mV). Try disconnecting the HO2S (Bank 1, Sensor 3), if the displayed voltage goes from over 1000 mV to around 450 mV, replace the HO2S (Bank 1, Sensor 3). Refer to Heated Oxygen Sensor (HO2S).

Never solder the HO2S wires. For proper wire and connector repairs, refer to Wiring Repairs.

TEST DESCRIPTION
The number below refers to the step number in the diagnostic table.

2. This step determines if the conditions necessary to set the DTC P0144 exist.