CODE 44 - LEAN EXHAUST INDICATION
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 .32 volt. The oxygen (O2) sensor varies the voltage within a range of about one 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 less than about 600°F (360°C). An open sensor circuit or cold sensor causes "open loop" operation. Code 44 is set when the O2 sensor signal voltage on circuit No. 412 remains less than .2 volt for 60 seconds or more and the system is operating in "closed loop".
Using the "Scan" tester, observe the block learn values at different RPM and airflow conditions. The "Scan" tester also displays the block cells, so the block learn values can be checked in each of the cells to determine when Code 44 may have been set. If the conditions for Code 44 exists the block learn values will be around 150. Check the following
- Oxygen sensor pigtail may be mispositioned and contacting the exhaust manifold.
- Check for intermittent ground in wire between connector and sensor.
- A Mass Airflow (MAF) sensor output that causes the ECM to sense a lower than normal airflow will cause the system to go lean. Disconnect the MAF sensor and if the lean condition is gone, replace the MAF sensor.
- Perform injector balance test, refer to CHART C2A - INJECTOR BALANCE TEST.
- 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 Code 44.
- 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 problem. See fuel system diagnosis CHART A7 - FUEL PRESSURE TEST.
- If there is an exhaust leak, the engine can cause outside air to be pulled into the exhaust across the oxygen sensor. Vacuum or crankcase leaks can cause a lean condition.
- If all of the above checks are okay, replace oxygen sensor.
