DTC 44

DTC 44 - Oxygen Sensor Circuit (Lean Exhaust Indicated):

Oxygen Sensor Wiring Circuit:

Circuit Description:

The ECM supplies a voltage of about .45 volt (450 mV) between terminals "YE14" and "YE15". (If measured with a 10 megohm digital voltmeter, this may read as low as .32 volt). The O2S varies the voltage within a range of about 1 volt (1000 mV) if the exhaust is rich, down through about .10 volt (100 mV) if the exhaust is lean.

The sensor is like an open circuit and produces no voltage when it is below about 360°C (600°F). An open sensor circuit or cold sensor causes "Open Loop" operation.

DTC 44 is set if the 02S signal voltage on CKT 412:
^ Remains below .3 volt (300 mV) for up to 4.5 minutes.
^ The system is operating in "Closed Loop."

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

1. Running the engine at 1200 RPM keeps the O2S hot, so an accurate display voltage is maintained. Opening the O2S 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 a faulty ECM.

Diagnostic Aids:

Use the Tech 1 to observe the long term fuel trim values at different RPM and air flow conditions. The Tech 1 also displays fuel trim cells, so that long term fuel trim values can be checked in each of the cells to determine when DTC 44 may have been set. If the conditions for DTC 44 exist, the long term fuel trim values will be around 150.

^ O2S Wire. Sensor pigtail may be mispositioned and contacting the exhaust manifold.
^ Check for intermittent ground in wire between connector and sensor.
^ Poor ECM Grounds. Check ground connections at transaxle stud and ECM connectors, making sure all connections are clean and tight.
^ 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). 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 DTC 44.
^ Vacuum or Crankcase Leaks can cause a lean condition.
^ Fuel Pressure. System will be lean if pressure is too low. It may be necessary to monitor fuel pressure while driving the vehicle 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.
^ If the above are OK, it is a faulty oxygen sensor.