DTC 44

Chart - Code 44 Oxygen Sensor Circuit, Lean Exhaust Indication:

Wiring Diagram for Oxygen Sensor Circuit:

CODE 44 - OXYGEN SENSOR CIRCUIT (LEAN EXHAUST INDICATED)



Circuit Description:
The Electronic Control Module (ECM) supplies a voltage of about .45 volts (450 mV) between terminals "D6" and "D7". (If measured with a 10 megohm digital voltmeter, this may read as low as .32 volts.) The 02 sensor varies the voltage within a range of about 1 volt, (1000 mV) if the exhaust is rich, down through about .10 volts (100 mV) if exhaust is lean. The sensor is like an open circuit and produces no voltage when it is below about 360C (600 degrees F) An open sensor circuit or cold sensor causes "Open Loop" operation.

Test Description:
Code 44 is set when the 02 sensor signal voltage on CKT 412 remains below .2 volts for 60 seconds or more and the system is operating in "Closed Loop".


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 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.
Also check:


02 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 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 or use MAF tester J-36101.


Lean Injector 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 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 "Fuel System Diagnosis" 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.

Air System (manual trans only) Be sure air is not being directed to the exhaust ports while in "Closed Loop". If the block learn value goes down while squeezing air hose to exhaust ports, refer to CHART C -6. If the above are OK, it is a faulty oxygen sensor.