DTC 44

Oxygen Sensor Circuit:

Circuit Description:
The PCM supplies a voltage of about .45 volt (450 mV) between terminals "BD2" and "BD3". (If measured with a 10 megohm digital voltmeter, this may read as low as .32 volt.) The O2 sensor varies the voltage within a range of about 1 volt (1000 mV) if the exhaust is rich, down to about .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). A Code 44, 45 or an open sensor circuit or cold sensor causes "Open Loop" operation.

Code 44 is set when the O2 sensor signal voltage on CKT 412:

^ Remains below .25 volt for up to 4.5 minutes.
^ The system is operating in "Closed Loop."

Code 44 Diagnostic Chart:

Test Description:
Number(s) below refer to circled number(s) on the diagnostic chart.

1. Running the engine at 1200 rpm keeps the O2 sensor hot to ensure the O2 sensor remains active and can read the exhaust oxygen content accurately.

2. Opening the O2 sensor circuit should result in a displayed voltage between 350 and 550 mV. If the display is still fixed below 350 mV, the fault is a short to ground in CKT 412 or a faulty PCM.


Diagnostic Aids:
Using the Tech 1, observe the block learn values at different rpm and air flow conditions. The Tech 1 also displays the block cells, so the block learn values can be checked in each of the cells to determine when the Code 44 may have been set. If the conditions for Code 44 exist, the block learn values will be around 150 or greater.

^ O2 Sensor Wire - Sensor pigtail may be mispositioned and contacting the exhaust manifold.
^ Check for intermittent ground in wire between connector and sensor.
^ Poor PCM to engine block ground.
^ MAF Sensor - A Mass Air Flow (MAF) sensor output that causes the PCM to sense a lower than normal air flow will cause the system to go lean. Disconnect the MAF sensor. If the lean condition is gone, replace the MAF sensor.
^ Lean Injectors - Perform injector balance test CHART C-2A. Testing and Inspection
^ Fuel Contamination - Water, even in small amounts, near the in-tank fuel pump inlet can be delivered to the injectors. The water causes a lean exhaust and can set a Code 44.
^ Fuel Pressure - System will be lean if pressure is too low. It may be necessary to monitor fuel pressure while driving the car at various road speeds and/or loads to confirm. Related Tests, Information and Procedures
^ Exhaust Leaks - If there is an exhaust leak, the engine can cause outside air to be pulled into the exhaust and past the sensor.
^ Vacuum or Crankcase Leaks can cause a lean condition and/or possibly a high idle.
^ If the above are OK, it is a faulty Oxygen (02) sensor.