Powertrain Controls - ECM/PCM

Code 44 Chart:

Code 44 Wiring Diagram:

CIRCUIT DESCRIPTION
The Electronic Control Module (ECM) supplies a voltage of about 0.45 volt (450 mV) between terminals "YD2" and "YD3". (If measured with a 10 megohm digital voltmeter, this may read as low as 0.32 volt.) The O2 sensor varies the voltage within a range of about 1 volt, (1000 mV) if the exhaust is rich, down through 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 316° C (600° F). An open sensor circuit or cold sensor causes "Open Loop" operation. Code 44 is set when the 02 sensor signal voltage on circuit 412 Remains below 0.25 volt for up to 4.5 minutes and the system is operating in "Closed Loop."

TEST DESCRIPTION
Numbers below refer to circled numbers on the diagnostic chart.

1. Running the engine at 1000 rpm keeps the 02 sensor hot, so an accurate display voltage is maintained. Opening the 02 sensor wire should result in a voltage display of between 350 and 550 mV. If the display is still fixed below 350 mV, the fault is a short to ground in circuit 412 or the ECM is faulty.

DIAGNOSTIC AIDS
Using the "Scan," observe the block learn values at different rpm and air flow conditions. "Scan" 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 exists, the block learn values will be around 150.

^ 02 sensor Wire - Sensor pigtail may be mispositioned and contacting the exhaust manifold. Check for intermittent ground in wire between connector and sensor.

^ Mass Air Flow (MAF) sensor - A MAF sensor output that causes the ECM to sense a lower than normal air flow will cause the system to go lean. Disconnect the MAF sensor and if the lean condition is gone, replace the MAF sensor.

^ Lean injector(s) - Perform injector balance test Chart C-2A.

^ 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 fuel 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. See Chart A-7.

^ 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.

^ If the above are OK, it is a faulty oxygen sensor.