Powertrain Controls - ECM/PCM

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

Oxygen Sensor Wiring Circuit:

Circuit Description:
The Powertrain Control Module (PCM) supplies a voltage of about .45 volt between terminals "PA12" and "PB6". (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 315°C (600°F). An open sensor circuit or cold sensor will cause "Open Loop" operation.

DTC 44 Will Set When:
^ O2S signal voltage remains less then .3 volt for 50 seconds or more.
^ The system is operating in "Closed Loop."
^ DTC 33 or 34 is not set.
^ "Closed Loop" integrator is active.
^ The TP sensor is between 5% and 93.8%.

Action Taken (PCM will default to): The Malfunction Indicator Lamp (MIL) will illuminate, and the cooling fan will enable.

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

1. This step determines if DTC 44 is the result of a hard failure or an intermittent condition.

Diagnostic Aids: DTC 44 or lean exhaust is most likely caused by one of the following:

^ 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. Related Tests, Information and Procedures
^ MAP sensor - An output that causes the PCM to sense a lower than normal manifold pressure (high vacuum) can cause the system to go lean. Disconnecting the MAP sensor will allow the PCM to substitute a fixed (default) value for the MAP sensor. If the rich condition is gone when the sensor is disconnected, substitute a known good sensor and recheck.
^ Fuel contamination - Water, even in small amounts, near the in-tank fuel pump inlet can be delivered to the injector. The water causes a lean exhaust and can set a DTC 44.
^ Sensor harness - Sensor pigtail may be mispositioned and contacting the exhaust manifold.
^ Engine misfire - A cylinder misfire will result in unburned oxygen in the exhaust, which could cause DTC 44. Refer to CHART C4-M and/or "Diagnosis By Symptoms." Chart C-4M Electronic Ignition System Misfire Diagnosis Testing and Inspection
^ Cracked Oxygen Sensor (O2S) - A cracked O2S or poor ground at the sensor, could cause DTC 44. Refer to "Diagnosis By Symptom." Testing and Inspection
^ Plugged fuel filter - A plugged fuel filter can cause a lean condition, and can cause a DTC 44 to set.
^ Plugged Oxygen Sensor (O2S) - A plugged reference port on the Oxygen Sensor (O2S) will indicate a lower than normal voltage output from the O2S.