Powertrain Controls - ECM/PCM

DTC 44 Oxygen Sensor Circuit (Lean Exhaust):

Oxygen Sensor Wiring Schematic:

CIRCUIT DESCRIPTION
The Powertrain Control Module (PCM) supplies a voltage of about 0.45 volt between terminals "D6" and "D7." (If measured with a 10 megohm digital voltmeter, this may read as low as 0.32 volt.) The Oxygen Sensor (O2S) varies the voltage within a range of about 1 volt if the exhaust is rich, down through about 0.01 volt if exhaust is lean.
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.

DTC 44 WILL SET WHEN
System is operating in "Closed Loop," O2S signal voltage is less than 0.150 volt for 3 minutes.

ACTION TAKEN (PCM WILL DEFAULT TO)
Vehicle will operate in "Open Loop" and Malfunction Indicator Lamp (MIL) will become illuminated.

DTC 44 WILL CLEAR WHEN
A current DTC 44 will clear when O2S voltage rises above the calibrated lean exhaust voltage threshold. A history DTC 44 will clear after 50 consecutive ignition key cycles without a current DTC 44 being stored.

DTC CHART TEST DESCRIPTION
Number(s) below refer to circled number(s) on the diagnostic chart.
1. The engine must be operating in "Closed Loop" to store DTC 44.

DIAGNOSTIC AIDS
Using the Tech 1 scan tool, observe the L.T. 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 exist, the L.T. fuel trim values will be around 172.
^ Oxygen Sensor (O2S) wire - Sensor pigtail may be mis-positioned and contacting the exhaust manifold.
^ Check for intermittent ground in wire between connector and sensor.
^ Manifold Absolute Pressure Sensor - A (MAP) sensor output that causes the PCM 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 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. See 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 (O2S).