Engine Control Module ECM

DTC 44 Chart:

DTC 44 O2S 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 Sensor (O2S) varies the voltage within a range of about 1 volt if the exhaust is rich, to about .10 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: The Oxygen Sensor (O2S) signal voltage on CKT 412:

^ Remains below .2 volt from 20 seconds to 225 seconds.

^ With the system operating in "Closed Loop."

Action Taken (ECM will default to): The Malfunction Indicator Lamp (MIL) will illuminate.

DTC 44 Will Clear When: Conditions for fault are no longer present and Tech 1 "Clear DTCs" function is used or 50 ignition switch keycycles have passed with no further faults or ignition switch is turned "OFF" and ECM B fuse is removed for 10 seconds.

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

1. Checks to see if DTC was set as result of a hard failure or intermittent condition. The next check is of the wiring and ECM.

Diagnostic Aids: Using a scan tool, observe the long term fuel trim values at different RPM and air flow conditions. The 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.

^ OXYGEN SENSOR (O2S) WIRE - Sensor pigtail may be mis-positioned and in contact with the exhaust manifold.

^ Check for intermittent ground in wire between connector and sensor.

^ FUEL CONTAMINATION - Water, even in small amounts near the in-tank fuel pump inlet, can be delivered to the injectors. Water intrusion 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. Refer to "A CHARTS/ FUEL SYSTEM DIAGNOSIS/ CHART A-6" 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.

^ AIR SYSTEM - Be sure air is not being directed to the exhaust ports while in "Closed Loop." If the long term fuel trim value goes down while squeezing air hose on left side of exhaust ports, refer to "C CHARTS/ AIR MANAGEMENT CHECK" .

^ CKT 413 - If CKT 413 is open, the voltage at terminal "D7" will be about .45 volt. This may also cause DTC 13 to set.

^ If all checks OK, the Oxygen Sensor (O2S) is faulty.