Federal Emissions

Code 44 Diagnostic Chart:

Oxygen Sensor Circuit Diagram:

CIRCUIT DESCRIPTION
The ECM supplies a voltage of about .55 volt between terminals "A16" and "A22". (If measured with a 10 megohm digital voltmeter, this may read as low as .35 volt.) The Oxygen Sensor (02S) varies the voltage within a range of about 1 volt. If the exhaust is rich, the 02S signal will display near 1 volt and when the exhaust is lean the O2S signal will display close to .1 volt.

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(s) below refer to circled number(s) on the diagnostic chart.

1. DTC 44 will set if:
^ No DTC 33 or DTC 34.
^ Voltage on CKT 412 remains below .2 volt for 60 seconds or more.
^ The system is operating in "Closed Loop."


DIAGNOSTIC AIDS:
Using the Tech 1 (or equivalent) scan tool, observe the long term fuel trim at different RPM and air flow conditions. The Tech 1 (or equivalent) scan tool also displays the block cells, so the long term 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 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.

^ Lean injector(s). Perform injector balance test CHART C-2A. 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 O2S signal 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 "Fuel System Diagnosis," CHART A-7. 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 (O2S).