CIRCUIT DESCRIPTION:The ECM supplies a voltage of about .45 volts (450mV) between terminals (purple and tan wire). (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, (1000mV) if the exhaust is rich, down throgh about .10 volt (100mV) if exhaust is lean. The sensor is like an open circuit and produces no voltage when it is below about 360 degree C (600f). an open sensor circuit or cold sensor causes "open loop" operation.
code 44 is set when the o2 sensor signal voltage on the o2 purple wire:
* Remains below .25 volt for up to 4.5 minutes.
* The system is operating in " closed loop"
TEST DESCRIPTION: Number(s) refer to circled number(s) on the diagnostic chart.
1. Running the engine at 1000 rpm keeps the O2 sensor hot, so an accurate display voltage is maintained.
Opening the O2 sensor wire should result in a voltage display of between 350 and 550mV. if the display is still fixed below 350mV, the fault is a short to ground in the o2 tan wire or the ECM is faulty.
DIAGNOSTIC AIDS: Using the "scan," observe the block learn values at different rpm and air flow conditions. The "scan" also displays the block cells, so the block learn value can be checked in each of the cell 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.
* O2 SENSOR WIRE sensor pigtail may be mispositioned and contacting the exhaust manifold.
* check for intermittent ground in wire between connector and sensor.
* MAF SENSOR A mass air flow (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
* 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 speed and/or loads to confirm.
* EXHUAST 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 sensor.
SOURCE: GM SERVICE MANUAL.
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