Powertrain Controls - ECM/PCM

Diagnostic Trouble Code 44:

Oxygen Sensor Circuit:

CIRCUIT DESCRIPTION
The Engine Control Module (ECM) supplies a voltage of about 0.45 volt between terminals "C13" and "C14." (If measured with a 10 megohm digital voltmeter, this may display as low as 0.32 volt). The Oxygen Sensor (O2S) voltage reads about 1 volt if a rich 02S signal is indicated, down through about 0.10 volt if a lean O2S signal is indicated.

The sensor is like an open circuit and produces no voltage when it is below about 315°C (600°F). An open sensor circuit or cold sensor causes "Open Loop" operation.

TEST DESCRIPTION
Number below refers to circled number on the diagnostic chart.

1. Diagnostic Trouble Code (DTC) 44 is set when the oxygen sensor signal voltage on CKT 412.

^ Remains below 0.2 volt for 50 seconds.
^ And the system is operating in "Closed Loop."

DIAGNOSTIC AIDS
Using the scan tool observe the long term fuel trim values at different RPM and air flow conditions to determine when the DTC 44 may have been set. If the conditions for DTC 44 exists 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.
^ Manifold Absolute Pressure (MAP) Sensor - A MAP sensor output that causes the ECM to sense a higher than normal vacuum will cause the system to go lean. Disconnect the MAP sensor and if the lean condition is gone, replace the MAP sensor.
^ Lean Injector(s).
^ 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. Refer to Chart A-7 Fuel System Diagnosis. Related Tests, Information and Procedures

^ Exhaust Leaks - If there is an exhaust leak, the engine can pull outside air 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.