DTC 44

Code 44 - Lean Exhaust Indication:

Wiring Diagram For Code 44 - Lean Exhaust Indication:

CODE 44 - LEAN EXHAUST INDICATION


Circuit Description:

The ECM supplies a voltage of about .45 volt between Circuits 412 and 413. (If measured with a 10 megohm digital voltmeter, this may read as low as .32 volts.) The O2 sensor varies the voltage within a range of about 1 volt if the exhaust is rich, down through about .10 volt if exhaust is lean.

The sensor is like an open circuit and produces no voltage when it is below about 310~C (600~F) An open sensor circuit or cold sensor causes "open loop" operation.

Code 44 is set when the average O2 sensor signal voltage at the ECM Circuit 412:

^ Remains below .2 volt for 20 seconds or more;
^ Time since engine start is 1-1/2 minutes or longer
^ Engine is in "closed loop" fuel control.


Test Description:

1. Grounding the diagnostic terminal with the engine running, enables the "Field Service Mode" and allows the ECM to confirm either open or closed loop operation.

2. A light out or "Open Loop" indicates the fault is present. Disconnecting the O2 sensor will raise the signal voltage above .2 volt. If the ECM and wiring are OK, the ECM should recognize the higher voltage, .35 to .55, and flash open loop when the engine is started.



Diagnostic Aids:

3. ^ The Code 44 or lean exhaust is most likely caused by one of the following:

^ Circuit 413 - If circuit 413 is open, the CKT 412 voltage at the ECM will be over one volt.
^ 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.
^ Fuel Contamination - Water, even in small amounts, near the in-tank fuel pump inlet can be delivered to the injector. The water causes a lean exhaust and can set a Code 44.
^ EGR - In normal operation, the ECM delivers less fuel and advances spark when EGR comes in. If the EGR does not open, the system will go lean and may have slight spark knock.
^ MAP Sensor - An output that causes the ECM to sense a lower than normal manifold pressure (high vacuum) will cause the system to go lean.
^ Oxygen Sensor - If the above are OK, and the instructions at the top of the chart will still set a Code 44, or "SERVICE ENGINE SOON" light is "OFF" more than "ON", or flashing "OPEN LOOP", it is a faulty Oxygen Sensor.
^ Air Control Valve - Check system operation.