DTC 44

Code Chart 44:

Oxygen Sensor Circuit:

CIRCUIT DESCRIPTION:
The ECM supplies a voltage of about 0.45 volts between terminals "C7" and "C8." (If measured with a 10 megohm digital voltmeter, this may read as low as 0.32 volts). When the oxygen sensor reaches operating temperature, it varies the voltage within a range of about .1 volt (exhaust is lean) to about 0.9 volt (exhaust is rich). The sensor is like an open circuit and produces no voltage when it is below about 316°C (600°F). An open sensor circuit or cold sensor causes "OPEN LOOP" operation.

TEST DESCRIPTION: The numbers below refer to circled numbers on the diagnostic chart.

1. DTC 44 is set when the oxygen sensor signal voltage on circuit 412 remains below 0.35 volt under the following conditions:

^ Engine run time after start is 2 minutes or more.
^ Throttle angle is greater than 5%.
^ These conditions exist for 25 seconds or more.

DIAGNOSTIC AIDS:
Using the "Scan" tool, observe the long term fuel trim value at different engine speeds. The "Scan" also displays the fuel trim 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 or higher. Check the following possible causes:

a. Oxygen Sensor Wire - Sensor pigtail may be routed incorrectly and contacting the exhaust manifold. Check for ground in wire between connector and sensor.
b. 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.
c. 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
d. 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.
e. If DTC 44 is intermittent, Testing and Inspection
f. A cracked or otherwise damaged O2S sensor may set an intermittent DTC 44.