DTC 44

Oxygen Sensor Circuit:

Circuit Description
The ECM supplies a voltage of about .45 volt between terminals "D6" and "D7". (If measured with a 10 megohm digital voltmeter, this may read as low as .32 volt. The Oxygen (02) sensor varies the voltage within a range of about 1 volt if the exhaust is rich, down through about .01 volt if exhaust is lean.

The sensor is like an open circuit and produces no voltage when it is below about 318°C (600°F). An open sensor circuit or cold sensor causes "Open Loop" operation.

Code 44 Diagnostic Chart:

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

1. Code 44 is set when:
^ Oxygen (02) sensor signal voltage is less than .150 volt for 3 minutes.
^ System is operating in "Closed Loop."


Diagnostic Aids
Using the Tech 1 "Scan" tool, observe the block learn values at different rpm and air flow conditions to determine when the Code 44 may have been set. If the conditions for Code 44 exist, the block learn values will be around 172.

^ Oxygen Sensor Wire - Sensor pigtail may be mispositioned and contacting the exhaust manifold. Check for intermittent ground in wire between connector and sensor.

^ 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 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 Code 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 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 (02) sensor.