P0144

Circuit Description
To control emissions of hydrocarbons (HC), carbon monoxide (CO) and oxides of nitrogen (NOx), a three-way catalytic converter is used. The catalyst within the converter promotes a chemical reaction which oxidizes the HC and CO present in the exhaust gas, converting them into harmless water vapor and carbon dioxide. The catalyst also reduces NOx, converting it to nitrogen. The powertrain control module (PCM) has the ability to monitor this process using the Bank 1 HO2S 2 and the Bank 1 HO2S 3 heated oxygen sensors. The Bank 1 HO2S 2 sensor produces an output signal which indicates the amount of oxygen present in the exhaust gas entering the three-way catalytic converter. The Bank 1 HO2S 3 sensor produces an output signal which indicates the oxygen storage capacity of the catalyst; this in turn indicates the catalyst's ability to convert exhaust gases efficiently. If the catalyst is operating efficiently, the Bank 1 HO2S 2 signal will be far more active than that produced by the Bank 1 HO2S 3 sensor. If the Bank 1 HO2S 3 signal voltage remains excessively high for an extended period of time, DTC P0144 will be set.

Conditions for Setting the DTC
- No related DTCs.
- Engine is operating in "closed loop."
- Engine coolant temperature is above 60°C (140°F).
- Closed loop" commanded air/fuel ratio is between 14.5 and 14.8.
- Throttle angle is between 3% and 19%.
- Bank 1 HO2S 3 signal voltage remains above 952 mV during normal "closed loop" operation for a total of 106 seconds over a 125-second period of time.

OR

- Bank 1 HO2S 3 signal voltage remains above 500 mV during deceleration fuel cut-off mode operation for up to 3 seconds.

Action Taken When the DTC Sets
- The PCM will illuminate the malfunction indicator lamp (MIL) the first time the fault is detected.
- The PCM will store conditions which were present when the DTC was set as Freeze Frame and in the Failure Records data.

Conditions for Clearing the MIL/DTC
- The PCM will turn the MIL "OFF" on the third consecutive trip cycle during which the diagnostic has been run and the fault condition is no longer present.
- A history DTC P0144 will clear after 40 consecutive warm-up cycles have occurred without a fault.
- DTC P0144 can be cleared by using the scan tool "Clear Info" function or by disconnecting the PCM battery feed.

Diagnostic Aids
Check for the following conditions:
- Fuel pressure - An excessively rich fuel mixture can load the catalyst, causing a DTC P0144 to be set. Refer to Fuel system Diagnosis.
- Rich injector(s) - Perform "Injector Balance Test."
- Leaking injector- Refer to Fuel System Diagnosis.
- Evaporative emissions (EVAP) canister purge - Check for fuel saturation. If full of fuel, check canister control and hoses. Refer to Evaporative Emission (EVAP) Control System.
- MAF sensor -The system can go rich if the MAF sensor signal indicates an engine airflow measurement that is not correct. Disconnect the MAF sensor to see if a rich condition is corrected. If so, replace the MAF sensor.
- Check for a leaking fuel pressure regulator diaphragm by checking the vacuum line to regulator for the presence of fuel. There should be no fuel in the vacuum sensor.
- TP sensor - An intermittent TP sensor output will cause the system to go rich, due to a false indication of the engine accelerating.
- Shorted Heated Oxygen Sensor (HO2S)- If the HO2S is internally shorted, the HO2S voltage displayed on the scan tool will be over 1 volt. Try disconnecting the affected HO2S with the key "ON," engine "OFF." If the displayed HO2S voltage changes from over 1000 mV to around 450 mV, replace the HO2S. Silicon contamination of the HO2S can also cause a high HO2S voltage to be indicated. This condition is indicated by a powdery white deposit on the portion of the HO2S exposed to the exhaust stream. If contamination is noticed, replace the affected HO2S.
- Open HO2S High or Low Circuit or Faulty HO2S - A poor connection or open in the HO2S high or low circuit can cause the DTC to set during deceleration fuel mode. An HO2S which is faulty and not allowing a full voltage swing between the rich and lean thresholds can also cause this condition. Operate the vehicle while monitoring the HO2S voltage with a scan tool. If the HO2S voltage is limited within a range between 300 mV to 600 mV, check the HO2S high and low circuit wiring and associated terminal connections.
- If none of above conditions are present, replace the affected HO2S.

Test Description
Number(s) below refer to the step number(s) on the Diagnostic Chart.
3. DTC P0144 being set during deceleration fuel cutoff mode operation may indicate a condition described in the "Diagnostic Aids" above. If the DTC P0144 test passes while the Failure Records conditions are being duplicated, an intermittent condition is indicated.
Reviewing the Failure Records vehicle mileage since the diagnostic test last failed may help determine how often the condition that caused the DTC to be set occurs. This may assist in diagnosing the condition.




Diagnostic Chart