DTC 44

Code Chart 44:

Oxygen Sensor Circuit:

CIRCUIT DESCRIPTION:
The ECM supplies voltage of about .45 volt between terminals "GE14" and "GE15." (If measured with a 10 megohm digital voltmeter, this may read as low as .32 volt.) The (Oxygen Sensor (O2S) varies the voltage within a range of about 1 volt if the exhaust is rich, down through about 10 volt if exhaust is lean.

The sensor is like an open circuit and produces no voltage when it is below about 316°C (6O0°F). An open sensor circuit or cold sensor causes "OPEN LOOP" operation.

TEST DESCRIPTION: Number(s) below refer to circled number(s) on the diagnostic chart.

1. DTC 44 is set when the O2S signal voltage on CKT 412:

^ Remains below .2 volt for 60 seconds or more.
^ And the system is operating in "CLOSED LOOP."

DIAGNOSTIC AIDS:
Using the scan tool observe the L.T. fuel trim values at different rpm and air flow conditions. The scan tool also displays the L.T. fuel trim cells, so the L.T. fuel trim values can be checked in each of the cells to determine when the DTC 44 may have been set. If the conditions for DTC 44 exist, the L.T. fuel trim values will be around 150.

^ O2S wire. Sensor pigtail may be mis-positioned and contacting the exhaust manifold.
^ Check for intermittent ground in wire between connector and sensor.
^ MAP Sensor. A shifted "Low" MAP sensor could cause the fuel system to go lean.
^ Lean Injectors. 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 DTC 44.
^ 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. Vacuum or crankcase leaks can cause a lean condition.
^ If the above are OK, it is a faulty oxygen sensor.