Powertrain Controls - ECM/PCM

Code 44 Diagnostic Chart:

Oxygen Sensor Circuit Diagram (Heated Sensor):

CIRCUIT DESCRIPTION:
The PCM supplies a voltage of about 0.45 volt (450 mV) between terminals "BD2" and "BD3". (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 following conditions exist:

^ The 02 sensor signal voltage on CKT 412 remains below 0.25 volt for up to 4.5 minutes
^ 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.
2. 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 CKT 412 or the PCM is faulty.

DIAGNOSTIC AIDS:
^ Poor ground connection to engine block from PCM.
^ Using the "Scan" tool, 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 pigtail may be mis-positioned 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 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 disappears, replace the MAF sensor.
^ Lean Injector(s) Perform injector balance test, Chart C-2A Fuel Injector Balance Test
^ 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.
^ 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. 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 or possibly a high idle.
^ If the above are OK, it is a faulty oxygen sensor.